cha 1

Chapter 1

Petroleum Geology of Venezuela

General geologyThe history of oil exploration

in Venezuela Petroleum basins

1P E T R O L E U M G E O L O G Y O F V E N E Z U E L A

1

Gulf of Venezuela

La Paz

Alturitas

El RosarioRo de Oro

Los Manueles

Las Cruces

Tarra

Urdaneta

Boscn

Lama

Mrida

San Cristbal

La Alquitrana

La VictoriaGuafita

Barinas

Silvn

SincoSilvestre

MERIDA

TACHIRA

COLOMBIA

BARINAS

APURE

Motatn

TRUJILLO

LamarLagocentro

CeutaTomoraro

LaConcepcin

W.Mara Mara Sibucara

Maracaibo MediaHombre Pintado

Las Palmas

Tiguale

El Mamn

Barquisimeto

San Felipe

CARABOBO

GUARICO

COJEDES

PORTUGUESA

ARAGUAMIRANDA

Valencia

Los Teques

Yucal - Placer

Roblecito ValleJobal

SabanIpire

Bella Vista

Punzn

Las Mercedes

Palacio

MACHETE

BelnRuiz

DakoaGuavinita

Tucupido

Copa Macoya

San Carlos

CaracasD.F.

Guanare

San Juande los Morros

San Fernandode Apure

Maracay

FALCON

LARA

CoroLa Vela

La Velaoffshore

Cumarebo

Mene de Maurda

Cabimas

Ambrosio

Ta JuanaLagunillas

Bachaquero

Mene Grande

ZULIA

BOLIVAR

1,300,000 m

1,200,000 m

1,100,000 m

1,000,000 m

900,000 m

800,000 m

700,000 m

600,000 m 100,000 m 200,000 m 300,000 m 400,000 m 500,000 m 600,000 m 700,000 m 800,000 m 900,000

100,000 m 200,000 m 300,000 m 400,000 m 500,000 m 600,000 m 700,000 m 800,000 m 900,000

LakeMaracaibo

YARACUY

Caribbean Sea

Tu y

Riv e

ruata

River

Gurico River

Apure River

Meta River

Arauca RiverAr

auca Ri ver

Ca tat umb

o River

Gu a

sare

Rive

r

Tocu yo

Rive

r

fig 1.36

fig 1.40

Fig 1.43

Fig

1.48

Fig

1

.48

Fig 1.45

Fig

1.48

LegendOil field State Boundaries

Cross Section

State Capitol

River

Gas field

Condensate field

Oil + Condensate field

00 20 40 60 80 miles

20 40 60 80 100 120 km

Trujillo

A p

ureRiv

er

Figure 1.0

Location map of oil fields in Venezuela.

1 2

BO

GUARICO

ARAGUAMIRANDA

ANZOATEGUI

MONAGAS

SUCRE

N. ESPARTA

Los Teques

Yucal - Placer

Roblecito ValleJobal

SabanIpire

BarsoBella Vista

Punzn

Las Mercedes

Palacio

MACHETEPAO

ORINOCO BELTHAMACA

CascaEl Roble

San Roque

San Joaqun

Santa AnaEl Toco

Guere

Budare ElotesTrico

Oficina

Chimire

Boca Nipa

Naroo

Guara

Dacin

Leona

Lobo

OscuroteOritupano

Adas

Melones

Acema - CasmaAcemaMata

Oveja

Kaki

Mapiri

Cantaura

Maulpa Carisito

Aguasay

Onado

Casma

La Florida

Santa Rosa

ZUATA

BelnRuiz

DakoaGuavinita

Tucupido

BarcelonaQuiamare

Cuman

La Ceiba

Greater Anacoarea

Greater Oficinaarea

Tacat

Pirital

JusepnMaturin

Temblador

Jobo

MorichalPiln

UracoaBombal

Tucupita

OrocualQuiriquire

El FurrialCarito

Greater Tembladorarea

ReclamationZone

Santa Brbara

Manresa

Ro CaribeLa Asuncin

CocheCubagua

MejillonesPatao

Posa

Dragn

Loran

Tajali

Trinidad

Pedernales

Copa Macoya

CaracasD.F.

San Juande los Morros

San Fernandode Apure

Maracay

BOLIVAR

AMACURO

BOLIVAR

1,300,000 m

1,200,000 m

1,100,000 m

1,000,000 m

900,000 m

00 m 700,000 m 800,000 m 900,000 m

00 m 700,000 m 800,000 m 900,000 m 1,000,000 m 1,100,000 m 1,200,000 m 1,300,000 m 1,400,000 m

DELTA

Bitor AreaCerroNegro

Caribbean Sea

Gulf of Paria

CiudadBolvar

Tobago

Tu y

Riv e

r

Margarita Island

Greater Anaco area Greater Oficina area

G ua nipa R

ive r

Tigre Riv e r

San Juan

River

Unare River

Orin

oco River

Caro

ni

Ri v

er

Aro

Rive

r

ZuataRive

r

Ca ur a Ri

ver

Gurico River

Apure River

Fig

1.48

Fig

1

.48

Fig 1.45

Fig 1.50 Fig 1.

50

Fig 1.55

Fig

1.48

IntroductionThe purpose of this chapter on the

Petroleum Geology and Basins of Venezuela

is to give the reader a general overview of

the geology of the country. Our knowledge

has been greatly enhanced by the oil

industry and mining activities that have been

ongoing for almost a century. Without

entering into a detailed analysis of the

numerous and unsolved problems with the

geology, we have integrated the information

presented in many papers and books written

on Venezuelan geology. We have tried to

attribute the original contributions of all

authors, and have also presented summa-

tions based upon our own experience. We

have avoided specialized and detailed points

of view concerning stratigraphy, sedi-

mentology and geotectonic evolution,

instead choosing to simplify the geology

because of our diverse readership and

limited writing space. For non-specialized

readers, we include a Glossary at the end of

the chapter, and also a time chart with the

main geological ages indicated and a

geopolitical map with all Venezuelan cities

and places cited in the text (Fig. 1.0). Also,

we include a section called the History of

Oil Exploration in Venezuela for those who

may be interested in the history and growth

of Venezuelas most important industry. At

the end of the chapter, a list of references

consulted for the compilation of figures and

text is provided. We also include references

to other papers and books that should be

useful to those who wish to study the

geology of Venezuelan petroleum basins in

more detail.

Physiographic provincesThere are five main physiographic

provinces in Venezuela (Fig. 1.1):

1. Mountain ranges

a.Venezuelan Andes system

b.Caribbean mountain system (Perij

Range, San Luis and Baragua Ranges, La

Costa Mountain Range)

2. Foothill regions

3. Coastal plains

4. Mainland plains

5. Guayana Province.

Rocks of a wide age range (Precambrian

through Neogene) are found in the

mountain ranges of La Costa and the Andes.

Their formation history is closely associated

with the evolution of the northern margin of

the South American plate from the Eocene to

the present. The foothill regions (9430 km2)

are covered by Neogene molassic sediments

whose main physiographic features are

terraces formed during glaciation/deglacia-

tion processes.

P E T R O L E U M G E O L O G Y O F V E N E Z U E L A

31

The Venezuelan physio-

graphic provinces are:

1) The mountain belts:

Venezuelan Andes and the

Caribbean Mountain System

(Perij, San Luis; Baragua

and La Costa Range); 2) the

foothills; 3) the coastal plains;

4) the plains between the

Orinoco River and the moun-

tain belts; 5) and the

Guayana Province or Massif

(after NB-18-ll map; MMH,

1976).

Maracaibo

S. Cristbal

Mrida Barinas

GuanareTrujillo

LakeMaracaibo

Coro

BarquisimetoValencia

Los TequesCaracas Barcelona

Cuman

Porlamar

Ciudad Bolvar

Carpano

Tucupita

Puerto Ayacucho

Caribbean Sea

BrazilColombia

Brazil

Colo

mbi

a

Trinidad

Gu

yan

a

Rio Orin

oco

AtlanticOcean

0

50

100

150

200 km

SanFernando

San Lui

s Range

Baragua

Range

Vene

zuelan

Ande

s Perij

Ra

nge La Costa Range C. de La Costa

Guaya

na

Massi

f

ArubaBonaire

La Tortuga Tobago

Grenada

Rio Meta

Rec

lam

atio

n Z

on

e

ArayaParia

Rio Arauca

Rio Apure

Rio PortuguesaRio G

uarico

Rio Tig

reR. Guan

ipa

Cariaco

72 68 64 60

72 68 64 60

11

7

3

11

7

3

0-100 m Plains andCoastal Plains

FoothillRegions

MountainBelts

100- 250 mSeaLevel

250

to >

500

0 m

Guajira Peninsula

Gulf of

Venezuela

ParaguanPeninsula

Interior Range(Central Branch)

Interior Range(Eastern Branch)

N

Maturn

Figure 1.1

1G E N E R A L G E O L O G Y P R E C A M B R I A N

4

The coastal plains (117,220 km2) are

concentrated in four broad regions: 1) north

of Falcn State (Fig.1.0), 2) Barcelona

coastline (Anzotegui State), 3) Orinoco

River delta (Delta Amacuro State), and 4)

north of Sucre State. The mainland plains

(260,000 km2), with an extensive drainage

network, encompass the land between the

northern mountain ranges and the Guayana

Province; they are the result of the

sedimentary filling of the Eastern and

Barinas-Apure Basins.

In the south is the Guayana Province

(also called Guayana Massif, Guayana

Shield, or Guayana Cratn in the

geological literature) with 425,000 km2 of

Precambrian-age terranes, with some

Pleistocene plains built by the Orinoco River

and some of its tributaries.

Precambrian terranes The Venezuelan Precambrian terranes

outcrop in the main mountain ranges of the

country and in the Guayana Province.

Because of the tectonic history of the north-

ern South American plate, both allochtho-

nous and autochthonous Precambrian rocks

are found. Figure 1.2 shows the distribution

of these terranes; those located north of the

Orinoco River were overridden by Paleozoic-

age crustal fragments that were accreted, or

added, to the South American plate.

The autochthonous terranes are located

in the Guayana Province, and also form part

of the basement of the Paleozoic to Cenozoic

sedimentary basins south of the Apure Fault.

There are four provinces of Precambrian

rocks in the Guayana Province: Imataca,

Pastora, Cuchivero and Roraima (Fig. 1.2).

It has not been possible to discriminate

different provinces (with respect to age) in

the basement of the oil basins to the north of

Guayana Province; this is because there are

few wells that have reached the basement in

these basins and the available descriptive

information is scarce.

The accretion of allochthonous terranes

on the South America plate began during the

Early Paleozoic (Caledonian Orogeny: 570 to

385 Ma); part of these rocks outcrop near

Mrida and San Cristbal in western

Venezuela. Later, during the Hercinian

Orogeny (385 to 245 Ma), occurred the

suturation, or welding of the allochthonous

blocks. These included Precambrian rocks,

among which only the granitic rocks of the

Sierra Nevada in the Santa Marta Massif

(Colombia) have been dated (Fig. 1.2). The

last collision began during the Cretaceous;

this allochthon includes rocks of

Precambrian age near the city of Caracas

(Federal District) and south of Valencia

(Carabobo State).

N

Cenozoic Orogenic Belt

Late Paleozoic Orogenic Belt

Early Paleozoic Orogenic Belt

Paleozoic and Cenozoic Basinsof the Precambrian Basement

Eastern Basin of the Precambrian Basement,Imataca Province Possible Extension

Imataca Province

Overthrusting

Pastora Province

Cuchivero Province

Roraima Province

Boundaries of theCordilleran Systems

Caracas

SantaMarta

East

ern

Ran

ge

Wes

tern

Ran

ge

UpperPaleozoicOrogenic

Belt Lower PaleozoicOrogenicBelt

Cenozoic OrogenicBelt

Paci

fic O

cean

Caribbean Sea6278

8

4

Caribbean FrontalThrust

Brazil

CuchiveroProvince

Valencia

BogotPaleozoic and CenozoicBasins as a Precambrian

Basement

Colombia

SanCristbal

Mrida

Apure Fault

Venezuela

CiudadBolvar

PastoraProvince

ImatacaProvince

Pana

ma I

sthm

us

Trinidad

300 km0

Guayana ShieldCuchiveroProvince

RoraimaProvince

Altam

ira Fa

ult

Rec

lam

atio

nZo

ne

Espin

o

Grab

en

Figure 1.2

Northern South Americas

distribution of allochthonous

terranes in which

Precambrian rocks are

present. These terranes

were sequentially sutured to

the South American

continent during the

Ordovician-Silurian and later

during Late Mesozoic

through Recent.

Paleozoic terranesThe rocks of Paleozoic age in Venezuela

are found in several regions, geologically

grouped as allochthonous or autochthonous

terranes of South America. The auto-

chthonous terranes are found in the

subsurface of the Barinas-Apure and Eastern

Basins (Fig. 1.21), south of the Apure Fault

(Fig. 1.3). These rocks are typical red beds

from Gondwana (South America and Africa

before its rupture) and Laurentia (North

America and Greenland before its rupture);

they are preserved only in the deep

structural depressions of these Venezuelan

basins. The allochthonous terranes are

distinguished by the age in which they were

tectonically accreted to the north of the

South American plate; there are those

accreted during the Early Paleozoic, others

during the Late Paleozoic and the latest

during the Mesozoic.

Distribution

Figure 1.3 shows the distribution of

allochthonous terranes that were welded to

the Lower Paleozoic autochthons during

OrdovicianSilurian time. Those rocks

accreted during the Lower Paleozoic are

now considered part of the basement from

the point of view of later Caribbean tectonic

history. They include that part of the

orogenic belt north of the Apure Fault, the

actual Andes and Maracaibo Basin.

In the Andes, rocks of the Lower

Paleozoic allochthonous terranes include

granitic and shelf/slope sedimentary rocks

(OrdovicianSilurian). Ordovician metase-

dimentary rocks are found in the subsurface

basement of the Maracaibo Basin and in the

Andes. Devonian-age allochthonous terranes,

welded to South America during the Late

Paleozoic, outcrop in the Perij Mountains.

Part of the accretionary history of the

Upper Paleozoic onto the Lower Paleozoic

includes granitic rocks, formed as a result of

subduction below the northern border of

South America. These include rocks of the El

Bal region (Permian age) and those found

in the subsurface of Eastern, Barinas-Apure

and Maracaibo Basins (Carboniferous age).

The accreted belt included sedimentary

sequences of Carboniferous and Permian

ages; these rocks now outcrop in the Perij

and Andes Mountains.

The last of these allochthonous terranes

is the Caribbean Mountain System that

extends from Guajira Peninsula (Western

North Venezuela) to Paria Peninsula (Eastern

North Venezuela), including the subsurface

basement of the Gulf of Venezuela and the

La Costa Mountain Range. In this terrane

Paleozoic rocks of Devonian to Permian

ages are found.


51

Guayana Shield


Upper Paleozoic Orogenic Belt

Lower Paleozoic Basin

Lower Paleozoic Orogenic Belt

Guayana Shield

Caracas

ReclamationZone

Brazil

Venezuela

Colombia

Espin

o

Grab

en

Altam

ira Fa

ult

Bogot

El Bal

SantaMarta

Caparo

East

ern

Ran

ge

Wes

tern

Ran

ge

UpperPaleozoicOrogenic

Belt Early Paleozoic Orogenic Belt

LowerPaleozoic

Basin


Caribbean Sea

62

62

78

78

8 8

4 4

CaribbeanFrontal Thrust

Apure Fau

lt

N

PanamIsthmus

0 100 200 300 km

Overthrusting

Boundaries of theCordilleran Systems

Pac

ific

Oce

an

Northern South Americas

distribution of allochthonous

terranes in which Paleozoic

rocks are present. These

terranes were sequentially

sutured during the

Ordovician and Silurian, then

during the Carboniferous and

finally during Late Mesozoic

through Recent.

Figure 1.3

1 6

Mesozoic terranes

Triassic-Jurassic

The Triassic is not present in Venezuela

or, at least, no evidence of its presence has

been found and documented. The oldest

part of the Jurassic system (208 to 181 Ma) is

represented by Volcnicas de la Ge (Perij)

and Volcnicas de Guacamayas (El Bal),

which predated the red bed sedimentation

of the La Quinta Formation and the whole

expansion process related to the Gulf of

Mexico or Proto-Caribe opening. They are

the lateral equivalents of the Volcnicas de

El Totumo (Perij) (Fig. 1.4),

In Venezuela, the Pangean continent

(the supercontinent comprising America,

Europe and Africa) rifting produced several

main structural features that later influenced

the evolution of the Venezuelan sedimentary

basins. Inside continental Venezuela, the

Proto-Caribe opening induced the

development of northeast-oriented exten-

sion valleys or grabens (Fig. 1.5). Among

these valleys are the Apure-Mantecal,

Espino, Andes-Perij and Maracaibo grabens.

It has been postulated that the Jurassic rocks

in the deepest parts of the Interior Mountain

Range of Eastern Venezuela were involved

in this deformation, as deduced by the trend

of the main grabens, such as Apure-Mantecal

and Espino. However, this theory has not yet

been proven.

All these grabens were filled during

the Jurassic by red bed (continental)

sediments, diverse volcanics, and occasional

shallow-marine clastics and limestones.

Their preserved sequences outcrop in many

places: the Guajira and Paraguan Peninsulas

(Cojoro and Cocinas Groups; Pueblo Nuevo

Formation), and the widespread La Quinta

Formation of Western Venezuela. They also

occur in the subsurface of Eastern Venezuela

Basin (Ipire Formation).

G E N E R A L G E O L O G Y P A L E O Z O I C A N D M E S O Z O I C

Age Perij and Guajira Andes Gurico and Cojedes La Costa Range

Jurassic

Triassic

Conglomerates

Seco Cojoro/COCINASLa Quinta

El TotumoMacoita

La GTinacoa Volcanics

La Quinta Ipire

Pueblo NuevoLas Brisas (Zenda)

Macuro

? ?

Guacamayas?

Figure 1.4

1

23

3

3

4

Caribbean SeaParaguan

Colombia

Perij

12 12

8 8

63

63

73

73

Andes

Coro

Caracas

Maturn

Maracaibo

EspinoGraben

Apure-MantecalGraben

Trinidad

Urica Fault

SantanderMassif

Guajira

0 100 200 300 km

El Pilar Fault

N

Figure 1.5

Correlation chart of the most

important Triassic-Jurassic

units in Venezuela.

Distribution of Jurassic rocks: 1) in Perij Range; 2) as part of the economic

basement of Maracaibo Basin; 3) in the Andes; 4) in Barinas-Apure and Eastern

Venezuela Basins (Apure-Mantecal and Espino Graben). It is believed that they are

involved in deep thrusting within Eastern Venezuelas Interior Range (after Bartok,

1993; Passalacqua et. al., 1995; and Lugo and Mann, 1995).

Cretaceous

Early Cretaceous. The major sedi-

mentary facies distribution and stratigraphy

of Early Cretaceous rocks (146 to 95 Ma) are

shown in Figs. 1.6 and 1.7.

In Western Venezuela, the sedimentation

was initially controlled by the Jurassic graben-

fault systems. This is evidenced by the

variable thicknesses of Rio Negro Formation

clastics, which range from more than 2 km

near the south of Machiques Trough, to only

a few meters thick in some places of the

North-Andean flank. Later the subsidence

stabilised and there was an extensive

transgression of an open sea over the Western

Venezuelan shelf causing the carbonate

sedimentation of the Cogollo Group. The

lateral clastic equivalent of these carbonates

in the Cratn or Guayana Province margins is

the Aguardiente Formation. In Central Vene-

zuela, there are some remains of an older


71

Barranqun

TEMBLADORCanoa

Peas Altas

Ro Negro

0 200 km

El Cantil

Mac

hiqu

esT

hro

ug

hU

riban

teTh

roug

h

Exposed Igneous and MetamorphicBasement (Guayana Shield).

Continental-Fluvial EnvironmentSandy Clastics

Coastal and Transitional EnvironmentSandy-Shale Clastics

Shelf EnvironmentCarbonates

Hemipelagic/PelagicLimestones and Shales

Sediment SupplyDirection

Chimana

Aguardiente

COGOLLO

SUCRE

GuayanaShield

(?) N

Figure 1.6

Age

Albian

Aptian

Barremian

Neocomian?

Ro Negro

Tib

MachiquesPich Apn

Lisure

Maraca COGOLLO

Perij and Lake Maracaibo

Andes and Barinas-Apure

La Grita (Capacho)

Aguardiente

GuimarosTib Apn

Ro Negro"Basal Clastics"

(Exotic Blocks)

?

?

Macaira Limestone?

?

Northern Gurico EasternInterior Range

Querecual(*)

( , "Valle Grande")CutacualChimana

"Gucharo"

El Cantil"El Mapurite"

Garca

Taguarumo

Picuda

Barranqun

Morro Blanco

Venados"Ro Solo"

"Punceres"

S

U

C

R

E

Sand / Sandstone Reservoir

Sand / Seal Pairs

Seal

Source Rock

The Querecual Formation extends to the Late Cretaceous

Carbonate Reservoir

(*)

?

?

Correlation chart of the most important Early Cretaceous units of Venezuela. Informal units are within quotation marks.

See Yoris, 1985, 1988, 1992, on Sucre Group.

Figure 1.7

Distribution of dominant sedimentary facies during the Neocomian-Albian (Early

Cretaceous) north of the Guayana Shield. Representative stratigraphical units of this

facies association are indicated.

1 8

(also Early Cretaceous) carbonate shelf,

which is discontinuous along the

deformation (mountain) front to the north of

Gurico State (Macaira Limestone).

In Eastern Venezuela, the sedimentary

history resembles that of a passive Atlantic

type margin. These rocks belong to the Sucre

Group, which at the base are sandy clastics

and some shelf limestones of the Barranqun

Formation (whose thickness is more uniform

than its Western Venezuela equivalent). Later,

extensive and well defined carbonate-clastic

shelf sedimentation was developed (El Cantil

and Chimana Formations). The main

difference with the Early Cretaceous of

Western Venezuela is that in the Interior

Range of Eastern Venezuela, the lower

contact with older sequences is unknown

and the thicknesses of the Early Cretaceous

units are greater. For example, the

Barranqun Formation is more than 1 km

thick everywhere, with massive, carbonate

shelf sedimentation in its middle part (Morro

Blanco Member of Barremian age114 to 118

Ma) in the northernmost outcrops.

The thickness of both El Cantil and Chimana

Formations is several times the thickness of

their lateral equivalent in Western Venezuela,

the Cogollo Group.

Late Cretaceous. The distribution of

paleoenvironments and stratigraphic units

during the Late Cretaceous is shown in Figs.

1.8 and 1.9. Figure 1.10 condenses the

correlation chart for these units for all of

Venezuela.

A diachronic and extensive marine

invasion began at the end of the Albian,

moving from east to west and invading the

south of Venezuela, which had been

emerged and undergoing erosion since Late

Jurassic and possibly Paleozoic times. This

marine invasion coincides with the

worldwide transgressive pulse of the Late

Cretaceous, recorded in America and Europe

through the sedimentation of organic-rich

limestones, shales and cherts; these rocks are

recognized in Venezuela as the Querecual-

San Antonio (Guayuta Group), Mucaria,

Navay and La Luna Formations. The

maximum transgression and lack of oxygen

is believed to have occurred between the

Turonian and the Campanian (72 to 91 Ma).

The La Luna, Navay and Querecual

Formations are the source rocks for the oil

basins of Venezuela, and were deposited

during the late Albian to the Turonian (95 to

88 Ma). The La Luna Formation ranges

between 50 and 300 m thick in Western

Venezuela, while the Navay Formation is

close to 600 m thick in the South-Andean

Flank and thickens to the northeast.

In Western Venezuela, the lateral facies

variations of these source rocks consist of

pelagic and phosphatic limestones, dark

shales and shelly limestones that grade to

sandy clastics and glauconitic facies in the

southeastern flank of the Andes in Tachira

State. In North-Central Venezuela, these

facies occur in the Mucaria Formation and

Guayuta Group .

G E N E R A L G E O L O G Y M E S O Z O I C

Dominant sedimentary facies

distribution during the

Cenomanian-Campanian

(Late Cretaceous) at the

northern edge of the

Guayana Shield North. Typical

units of these sets of facies

are indicated.

Continental-Fluvial Sandy Clastics

Coastal and Transitional Sandyand Shaly Clastics

Bathyal (Pelagic) and Shelf ShalyLimestone, Chert and Siliceous Mudstone

Bathyal and Abyssal Hemipelagic/Pelagic Shales and Limestones

Igneous-Metamorphic Basement(Guayana Craton) Shelf Carbonates

?

Socuy Mucaria La Luna

Capacho Navay

Escandalosa TEMBLADOR

0 200 km

N

Maracaibo

CaracasMaturn

Barcelona

Gua

yac

n

Guayana Shield

Infante GUAYUTA

Figure 1.8

The Guayuta Group is thickest in North-

Eastern Venezuela, being more than 1 km thick

in its type area (Anzotegui State). In the

Eastern Basin, this unit changes laterally to the

south, losing its source rock character by giving

way to sedimentation from shallower

environments, from shelf to coastline and even

continental, which are defined in the

subsurface as the Canoa and Tigre Formations

(Temblador Group).

The Late Cretaceous in Venezuela ends in

the Maastrichtian, with units that are regressive

relative to the deeper environments of the

source rock.

In Perij and the Maracaibo Basin,

the La Luna Formation grades vertically to

glauconitic limestones (Socuy Member), and

dark shales with thin sandstones defined as

the Colon and Mito Juan Formations. In

the North-Andean Flank, the glauconitic-

phosphatic Tres Esquinas Member is present,

which is the possible diachronic equivalent of

the Socuy Member, underlying the dark shales

of the Coln Formation.

In the South-Andean Flank, the upper

contact with the source rock is gradational to

erosive with the basal sandstones of Burgita

Formation.


91

Sandy Clastics Clay-Silt Clasts

Shallow MarineCarbonates

Positive Areas

Sedimentary SupplyDirection

Postulated Depocenter Axis

Thrust Front

?

?

?

?

? ?

?

Defor

matio

n

Front

Adva

nce

Mito Juan

CujisalSan Juan

Marine Sediments (Undifferentiated)

Coln

Ro de Oro

N

Igneous-MetamorphicBasement

GuayanaShield

Burgita

Positive areas that includePaleozoic and Mesozoic rocks

Figure 1.9

Age

Maastrichtian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

Perij and Lake Maracaibo Flank

North-AndeanFlank

South-Andean North ofGurico

Southern FlankEastern Basin

EasternInterior Range

Mito Juan Mito Juan

Coln Coln

Socuy

La Luna

(Regional hiatusat the base?)

Tres Esquinas

Guayacn

Capacho

Seboruco

Burgita

Quevedo

Nav

ay

La Morita

Guayacn / Caliza "O"

Escandalosa

Gurico

?

?

?

"Exotic Blocks "

Tigre

TEMBLADORGROUP

Canoa Querecual

San Antonio

San JuanVidoo

Reservoir (Carbonate)

Reservoir (Sandy)

Sand / Seal Pairs

Seal

Source Rock

Infante

(Mucaria, San Antonio, Querecual,

" )"Ro Chvez"

"Querecual of the North

GUAYUTA

G

U

A

Y

U

T

A

La Luna

?

Figure 1.10

Sedimentary facies distribution during the Maastrichtian (Late Cretaceous) at the

northern edge of the Guayana Shield. Typical units of these sets of facies are

indicated. Notice that the axis of the Western Venezuela depocenter is subparallel

to the deformation front, as a consequence of the plate collision between Nazca

and South American plates.

Correlation chart of the most important Late Cretaceous units of Venezuela. Gurico and Vidoo Formations

continue through the Paleocene; Canoa and Querecual Formations start by the end of Late Albian.

1 10

In North-Central Venezuela, the lateral

equivalents of the Mucaria Formation grade

vertically to the hemipelagic and turbidite

sequences of the lower Guarico Formation.

To the east, the bathyal sandstones of the San

Juan Formation overlie the black cherts and

sandstones of the San Antonio Formation.

Then, in turn, the San Juan Formation grades

vertically to the dark shales of the Vidoo

Formation (late Maastrichtian60 to 65 Ma).

Cenozoic terrains

Paleogene

Paleocene-Eocene of Western Venezuela.

During late Cretaceous (Fig. 1.9) to early

Paleocene, Western Venezuela was affected

by the collision between the Nazca Plate

(Pacific Ocean) and Western Colombia. There

is evidence that the sedimentation of the

Orocu Group (and probably Guasare and

Marcelina Formations) was controlled by the

deformation fronts of this collision (Fig. 1.11).

These fronts generated successively younger

depocenters to the east of the actual Perij

Mountain range.

Figure 1.11 summarizes the sedi-

mentation and gradual evolution of the

deformation front as the Caribbean plate

passed north of the South American plate

during the Paleocene-Eocene. For simplicity,

several formations are summarized by one

name only (e.g., Misoa refers to the

sedimentation of lateral equivalents and/or

closely related units, such as the Misoa, Cas

and Pauj Formations). Each event carries

the most distinctive formation or group name.

To the northeast of the South American

plate, the oblique collision of the Lesser

Antilles arc generated a series of sheets, or

nappes, trending towards the south and

southeast. These control the turbidite

sedimentation of formations such as Trujillo

and Morn.

G E N E R A L G E O L O G Y C E N O Z O I C

V

V

V

V

V

Misoa

Orocu/Mirador

Orocue/Mirador

Gurico

Trujillo

Misoa

Gobernador

Humocaro

La Victoria

Pagey

Shallow Clastics

Caribbean Plate

Maracaibo-Sta. Marta

BlockCentral American Arc

Andean Block

ShallowClastics

ShallowClasticsW

este

rnR

ange

of

Col

ombi

aC

ollis

ion

N

SM-B

B

Maracaibo

Gobernador

MatatereMorn

Foredeep

La Victoria

Mar

ine

Clas

tics

Early Paleocene *

Early Eocene*

Middle Paleocene *

Faralln Plate

Trujillo

Guasare/Marcelina

South AmericanBlock

(*) Deformation Front Position

EL Bal Lineament

Roblecito

Gurico

Barcelona

Carbo

nates

Lesser Antilles Arc

Guayana Shield

0 50 km

= Barco-Los Cuervos-Mirador-Carbonera Fms. Event (Paleocene-Eocene)

= Garrapata-Gurico Fms. Event (Paleocene)

= Trujillo Fm. Event (Paleocene-Eocene)

= Misoa-Cas-Pauj Fms. Event (Eocene)

= Direction of sediment supply

= Gobernador-Masparrito Fms. Event (Eocene)

= Humocaro-Quebrada Arriba Fms. Event (Eocene)

= La Victoria-Santa Rita-Jarillal Fms. Event (Eocene)

= Exposed areas

= Thrust front

Humocaro Peas Blancas

Truj

illo

Pauj

Figure 1.11

ESE migration of the

Caribbean deformation front

and associated episutural

sedimentation during

Paleocene-Eocene times.

The Andean-South American

boundary was located at

the present position of the

Santa Marta-Bucaramanga

(SM-B) and Bocono

(B) fault systems.

On the other hand, during the

Paleocene, to the north and west of

Maracaibo Basin, the Guasare Formation

was deposited in shallower environments

further away from the deformation fronts,

and afterwards the Marcelina Formation in

coastal-marsh environments.

During the Eocene, a complex sedi-

mentary setting existed in the Maracaibo

Basin. Distinct deltaic/estuarine, coastal/fluvial

and marine systems developed, depending on

their geographic position with respect to the

different deformation fronts, such as in Perij

or later on in Lara to the east. Formations such

as Barco-Los Cuervos and Mirador-Carbonera

(deposited between the Paleocene and Middle

Eocene65-40 Ma) represent two similar

sedimentary pulses of fluvial-deltaic origin in

the western part of Maracaibo Basin. In the

central part of the basin, the Guasare, Trujillo,

Misoa, Cas and Pauj Formations were more

marine lateral equivalents of the Barco-Los

Cuervos and Mirador-Carbonera, with a

relative, gradual deepening of environments

to the northeast. In the Barbacoas region, east

of Trujillo State, the average depth of the

Eocene sea was shallow enough to deposit

the transitional and coastal-marine sediments

of Gobernador-Masparrito and Humocaro-

Quebrada Arriba Formations. Meanwhile, in

Falcn State just north of the south-verging

deformation fronts, the La Victoria-Santa Rita

and Jarillal Formations were deposited. This

sedimentation was associated with exten-

sional basin subsidence related to along-strike

faulting (i.e., a pull- apart basin) (Fig. 1.12).

Paleocene - Eocene of North -Central

Venezuela. Part of the accretion due to the

Lesser Antilles is probably represented by the

sediments of the Gurico Formation, plus the

limestone and other older units in the

olistostromes. During the Paleogene and

Neogene, this fold and thrust belt migrated to

the south and east of the nothern margin of


111

?

Pull-Apart Basin

200 Km

Foredeep Sediments Thrust Front

Positive Areas

Shallow Clastic Sediments

Volc

anic

Arc

CaribbeanPlate Late Eocene

?South American Plate

Frontal Thrust

N

Advance of Allochthonous Terranes

Oca Fault System

MaximumSubsidence Area

Figure 1.12

XX

V

V

?

Paleocene-Eocene

Caribbean PlateExtinct Volcanic Arc

LesserAntilles

Positive Area

AtlanticOcean

Pampatar-Punta Carnero

Vidoo-Caratas

??

?

?

?

??

Peas Blancas

Maturn

0 50 Km

Slop

e

Barcelona

South American Plate

Roblecito

Clastic Shelf

N

Oceanic Sedimentation (Undifferentiated)

Caribbean DeformationLimit

Act

ive

Volc

anic

Arc

Foredeep Tinajitas

Shallow Sandy Clastics

Turbidites

Limestones

Lime-Clay Clastics Predominate over the Sandy Clastics (Slope Environment)

Direction of Sediment Supply

Positive Areas

Thrust Front

Caratas

Figure 1.13

Generation of pull-apart basins at the boundary between the Caribbean and South

American plates; the maximum subsidence areas were located north of Falcn State

at this time (Late Eocene) (after Macellari, 1995).

Regional geologic framework for the sedimentation at the northern flank of the

Eastern Basin during the Paleocene-Eocene.

1 12

the South American plate. Those rocks

originally sedimented in the trough just in

front of the belt (the foredeep) were later

uplifted, eroded and re-sedimented into

the trough.

While the Caribbean plate moved to the

east between the South American and North

American plates, the influence of the fold

and thrust belts also moved, but to the

south, producing the new foredeep of the

Roblecito Formation, with a probable age

between the Late Eocene and Oligocene (?)

(39-23 Ma). South of the new foredeep, the

lithosphere bent due to the new load,

causing the influx of the clastics that

produced the La Pascua Formation.

Paleocene-Eocene of Eastern Venezuela.

During the Paleocene and Early Eocene, the

sedimentation was not influenced by the

Caribbean deformation fronts. The Vidoo

(hemipelagic marls, siltstones and clays) and

Caratas (sandstones) Formations accumu-

lated on a passive continental margin slope.

It is possible that the influence of the

oblique collision of the Caribbean plate on

Eastern Venezuela began in the Middle

Eocenethe first evidence may be in the

sandy-glauconitic and foraminiferal-rich

carbonates deposited on the foredeep

margins located north of Venezuela (Peas

Blancas and Punta Carnero Formations and

Tinajitas Member of Caratas Formation). On

Margarita Island, the sandy and carbonate-

rich turbidites of the Pampatar (sandy rich)

and Punta Carnero (carbonate rich)

Formations represent a separate sedimen-

tation from the Gurico and Roblecito, both

in time and space, and are probably related

to accretion near Barbados.

Figure 1.13 summarizes conceptually

the relationship between stratigraphic units

and deformation fronts. Figure 1.14 sum-

marizes the Paleocene-Eocene stratigraphic

nomenclature, emphasizing the potential

character of each unit as a seal or reservoir.


?

?

?

San Juan

Vidoo

Caratas

Tinajitas

?

La Pascua/ Los Jabillos?Roblecito

PeasBlancas

?

Gurico

Cerro Misin

La Victoria

Santa Rita

?

Coln

Trujillo

Humoca

Mora

nro

Valle

Hondo

(Misoa/Qda. Arriba/Gobernador)

Masparrito

PageyMene Grande

Pauj

Cas

Carbonera CarboneraPauj

(Mirador/La Sierra) (Misoa/Mirador)

Los Cuervos

Marcelina

Colon/mito Juan

Western Venezuela:Trujillo, Lara and South-Andean

Flank and Barinas-Apure Falcn Eastern Venezuela

(?) Garrapata

?

?

Seal

Eroded Interval

Eroded/Unconformable

Reservoir (Carbonate)

Reservoir (Sandy)

Sand/Seal Pairs

Coln/Mito Juan

Age

Eocene

Paleocene

Maastricht

Western Venezuela: Perij, LakeMaracaibo, North-Andean Flank

BarcoGuasare Barco

OROCUE

North-CentralVenezuela

Los Cuervos

Jarillal

OROCUE

?

?

Figure 1.14

Correlation chart for the

Paleocene-Eocene of

Venezuela. The Coln

Formation extends into the

Campanian; the Carbonera,

Pauj, La Pascua, Roblecito

and Los Jabillos Formations

extend into the Oligocene.

The Gurico Formation may

reach down to the top of the

Maastrichtian wherever the

Garrapata Formation is

absent.

Oligocene of Western and North-Central

Venezuela. Since the Oligocene, the

sedimentary accumulation in Maracaibo

Basin was preserved mainly on its flanks. To

the west are the sandy clastics of the

Carbonera and Ceibote Formations (El

Fausto Group), to the south and east are the

fine clastics of the Len Formation (Fig.

1.15), and to the center is the Icotea

Formation (assigned by several authors to

the Oligocene). The Icotea is only found in

structurally controlled depressions, and its

characteristic lithology consists of siltstones

and claystones, with minor proportions of

sandstones.

The Falcn Basin reached its maximum

development and deepening during the

Oligocene. The sedimentation in the Falcn

region resulted from a different tectonic

setting than that of the Maracaibo Basin,

Barinas-Apure and Eastern Basins. Figure

1.16 shows the extensional basins associated

with major strike-slip faulting, especially in

the north of Falcn State. These gradually

evolved to the east, while the Caribbean

plate moved in the same direction.

In the north of central Venezuela, the

trough containing the Roblecito Formation

migrated to the east and southeast, favoring

the advance of La Pascua sandstones to the

south. These were followed and overlaid by

clastics from the foredeep.

Oligocene of Eastern Venezuela. During

the latest Eocene and Oligocene, the

sedimentation in the Interior Mountain

Range is represented by the Los Jabillos

(diverse sandy clastics), Areo (fine marine

and glauconitic clastics) and part of the

Naricual (shallow marine and coastal-fluvial

pelitic and sandy clastics) Formations.


131

Positive Areas

Thrust Front

Depocenter Axis

Extensional Basin


Area Positive

PositiveArea

Positive Area

El BalArc

La Pascua

Carbonera

Len Guafita

San Luis / Patiecitos

Pecaya/Agua S

alada

Churuguara

CasupalCastillo

Positiv

e Area

GuayanaShield

Shallow SandyClastics

Sandy and PeliticClastics of Shallow andDeep Environmen(Turbidites)

Pelitic Clastics ofShallow Marine Environment

Limestones

Direction ofSediment Supply

0 50 km

?

??

??

?

?

?

Colombia

?

Guacharaca

El Paraso

Roblecito

N

Figure 1.15

Oligocene-Miocene Caribbean Plate

Oca Fault System

South American Plate

UrumacoTrough

La Vela Cove

La Pascua-Roblecito

Frontal Thrust Advance

(Central-North)

Capiricual-Carapita(Eastern)

ExtensionalTrough

Positive AreasShallow ClasticSediments Plate Movement

Vectors

200 km

N

Basin"Foreland"Incipient

Thrust Front

MainDepocenter

Figure 1.16

Sedimentary regional framework in Western Venezuela (Maracaibo, Falcn, Barinas-

Apure Basins and Gurico Sub-Basin) during the Oligocene. The main depocenters

are located in Tchira (Len Formation), Falcn (Pecaya and Agua Salada Formations)

and Gurico (Roblecito Formation).

Maximum development of the Falcn State pull-apart and generation of extensive positive

areas in Maracaibo Basin and northern Falcn. Toward the south and east, the foreland

basin evolved, developing "troughs" like those of the La Pascua-Roblecito Formations (Late

Eocene-Oligocene) and Carapita-Capiricual (Early-Middle Miocene) (after Macellari, 1995).

Figure 1.18

1 14

Figure 1.17 summarizes conceptually

the relationship between the stratigraphic

units and deformation fronts. The double

sediment source for the Naricual Formation

and its equivalents (e.g., Quebradn

Formation) is shownon the north side is a

fold-and-thrust belt source, and on the south

side is a Cratn Interior source. Something

similar occurs with the La Pascua and

Roblecito Formation equivalents, called the

Merecure Formation in the subsurface of the

southern flank of the Maturn Basin.

Following the diachronism principle, it is

assigned a younger age (Miocene), similar to

the surface Merecure Group.

Figure 1.18 summarizes the Oligocene

stratigraphic nomenclature, characterizing the

units as potential seals or reservoirs.

Neogene and Quaternary

In Venezuela, the Neogene is

characterized by important mountain-

building episodes, which are a direct

consequence of the Caribbean and South

American plate interactions. Figures 1.15 and

1.16 show in a general way the beginning of

the Andean uplift, and the structures

generated by the eastern movement of the

Caribbean plate between the North

American and South American plates during

the Late Oligocene to Early Miocene.


Regional geologic framework for the sedimentation at the north flank of the Eastern

Basin of Venezuela during the Oligocene. There is a strong difference between the

Naricual in the subsurface and as defined in its type region: the "Merecure Formation"

name has been used for subsurface equivalents of the Merecure Group formations

(Los Jabillos, Areo and Naricual Formations) that crop out in the Interior Range.

X XX

vv

Extinct Island Arc Limit of the Caribbean Deformation

Caribbean Plate

Slo

pe

Naricual/Quebradn

?

?

?

N

??

La PascuaClastic Shelf/Transitional

Environment/Deltas

Barcelona Los Jabillos

Merecure/"Naricual"

Chaguaramas

Merecure

Direction of SedimentSupply

Positive Areas

Thrust Front

Silt-clay Clastics Predominate overthe Sand Fraction (Slope Environment)

Shallow Sandy Clastics

0 50 km South American PlateOligocene

Roblecito Areo(?) Areo(?)

Activ

e Isla

ndA

rc

Figure 1.17

Eroded/Unconformable Contact

Sandy Reservoir

Sand/Seal Pairs

Seal

Eroded Interval

Age

Oligocene

Late Eoc.

Western Venezuela Perij

Lake Maracaibo, North-Andean Flank

Western Venezuela Falcn Basin

Ceibote

Len

Car

bo

ner

a

Pauj/Mene Grande

Carbonera

?

PALMAR/PARANGULA

El Paraso

(Churuguara/Castillo/Pecaya/San Luis/Agua Salada)

Naricual

Quebradn

Roblecito

La Pascua?

Naricual

Areo

?

Los Jabillos

Palmar Palmar/ParngulaG

u

a

fGuardulio

Caratas/Roblecito ?

MERECURE

?

Pagey(?)

Western Venezuela, Trujillo, Lara, South-Andean Flank

and Barinas-Apure

North-CentralVenezuela Eastern Venezuela

?

Icotea

Arauca

t

a

i

Correlation chart of the most important Late Eocene through Oligocene units of Venezuela. Pauj, Mene Grande and Pagey Formations

extend into Middle Eocene; El Fausto Group and Churuguara, Castillo, Pecaya, San Luis, Agua Salada and Quebradn Formations extend

into the Miocene.

Figure 1.18

1During this time, extensional (Falcn Basin)

and foreland basins were created. In

Western Venezuela, the Barinas-Apure

foreland basin was influenced by the

formation of the Colombian and Venezuelan

Andes. The Eastern Venezuela basins

resulted from the oblique collision between

the Caribbean plate and the northwestern

margin of the South American plate. In the

Pliocene (Figs. 1.19 and 1.20), the uplifting

of Northern Venezuela produced the

present-day distribution of petroleum basins

(Fig. 1.21) and generated the La Costa and

Venezuelan Andes mountain ranges

(dividing the Maracaibo and Barinas-Apure

Basins). Figure 1.22 summarizes the

Neogene and Pleistocene stratigraphic units,

showing their potentiality as source rocks,

seals or reservoirs.

In Western Venezuela, the Andean uplift

produced significant thicknesses of molasse

sediments (Guayabo Group, and La Villa, La

Puerta and El Milagro FormationsFig. 1.22).

In places, both the North-Andean and South-

Andean flanks have molasse sediments that

reach more than 5 km thick (15,000 ft). In the

Perij Mountain range, the El Fausto Group is

the molasse-equivalent unit, and is related to

the mountains of the deformation front on

the west side of Maracaibo Basin.


15

?

?

Continental Environment Conglomeratesand Sandy Clastics

Deltaic-Fluvial Environment, Sandand Pelitic Clastics

Open-Marine and Foredeep Environment,Pelitic Clastics

Sediments Supply

Fluvial and Coastal Environment Sandy Clastics

Shallow Environment Carbonates

Positive Zones

Thrust Front

El Pilar Fault

Oficina-FreitesMerecure

El Bal Arc

Per

ij R

ange

Chaguaramas

Ande

sColom

bia

Caribbean PlateAgua Salada

Capadare

Barb

ados

Pris

m

La Costa Range

Coro

0

50

100

150

200 km

UrumacoCaujaraoSocorro

CapiricualQuiamareQuebradn

Quiamare

Carapita La Pica

Isla

nd A

rc

La RosaLagunillas La Puerta

LakeMaracaibo

GUAYABOMrida

Oca Fault

Quiriquire

Guayana Shield


N

Las Piedras

Parn

gula

- Ro Y

uca

El Bal Arc

QuebradnQuiamare

Merecure

Guayana Shield


Guayana Shield

Barb

ados

Pris

m

Isla

nd A

rc

CarapitaLa Pica

CapiricualQuiamare

QuiriquireLas Piedras

El Pilar Fault

MerecureChaguaramas

Oficina-Freites

Ande

s

MridaGUAYABO

La RosaLagunillas La Puerta

LakeMaracaibo

Perij

Ra

nge

La Costa Range

Oca Fault Capadare

UrumacoCaujaraoSocorro

Agua Salada

Colombia

Caribbean Plate

Coro

0

50 150

100 200 km

Parg

ula-R

o Yuca

?

?

Continental Environment Conglomeratesand Sandy Clastics

Deltaic-Fluvial Environment, Sandand pelitic Clastics

Open-Marine and Foredeep Environment,Pelitic Clastics

Fluvial and Coastal Environment Sandy Clastics

Shallow Environment Carbonates

Positive Zones

Regional geologic framework for the sedimentation in all Venezuela (Maracaibo, Falcn, Barinas-Apure and Eastern basins) during the

Miocene-Pliocene. The largest accumulations of continental sediments occur on the flanks of the Andes and La Costa Range. The most

important reservoirs of Venezuela were deposited during this epoch: La Rosa, Lagunillas, Isnot (Guayabo Group), Carapita, Oficina,

Chaguaramas and Merecure Formations.

Figure 1.19

1 16

The La Rosa and Lagunillas Formations

predate the distal environments of the Perij

and Andes molasses. The La Rosa Formation,

with its basal sandstones (Santa Brbara

Member), is of major petroleum importance.

Its characteristic middle shale interval has

lateral sandy variations that are important res-

ervoirs in the eastern coast of Lake.

Maracaibo. Its thickness varies from 70 to

1100 m (230 to 3600 ft) because the unit was

deposited over an irregular erosional surface

and is fault-controlled. The La Rosa

Formation is believed to be Early to Middle

Miocene age (20 to 15 Ma).

The Lagunillas Formation overlays

the La Rosa and consists of transitional

shallow, coastal, and continental sediments

that reach more than 1000 m (3280 ft) thick

in the center of Maracaibo Basin.

It is a very important reservoir in the eastern

coast fields, where it has been divided into

five members, all of which have oil

potential. It is equivalent in age (Middle to

Late Miocene15 to 6 Ma) to the La Puerta

Formation and part of Guayabo and El

Fausto Groups.

In the Barinas-Apure Basin, the

Parangula and Ro Yuca Formations

(continental sediments) are the distal

equivalents of the Guayabo Group.

In the Falcn region, open sea

environments can be found, ranging from

deep-marine turbidites (e.g., Pecaya Forma-

tion) to shallow clastics (e.g., Cerro Pelado

Formation) and carbonates (e.g., San Luis

Formation). The final filling of the Falcn

Basin during the Pliocene was with the

conglomeratic-marine clastics of La Vela

Formation and the continental Coro

Conglomerate (Pliocene-Pleistocene).

In North-Central Venezuela, the main

environments of deposition are fluvial and

continental, resulting in the upper Que-

bradon and Quiamare Formations. They

increase in thickness considerably to the east

and south.


Pliocene/Recent

BoconFault

San SebastinFault

Ande

s

South-AmericanPlate

Trujillo

Range

FalcnBasin

200 km

N

Positive Areas Thrust FrontShallow ClasticSediments Plate Movement

Vectors

MaracaiboBasin

Maximum Subsidence Areas

Caribbean Plate

Oca Fault

Curazao Prominence

North of Venezuela Deep

Figure 1.20

72 68 64 60

72 68 64 60

11

7

11

7

Guaya

na

Massi

f

Colombia

Barinas-ApureBasin

S. Cristbal

Barinas

Trujillo

Vene

zuela

n And

es E.B.L

La Costa RangeMaracaiboBasin

Perij

Ra

nge

MaracaiboFalcnBasin Caracas Cuman La Costa Range

BarcelonaMaturn

GuricoSub-basin

Eastern Basin

Porlamar

MargaritaBasin

Caribbean Sea

TrinidadAtlantic

Ocean

Orinoco Belt

Coro

Guy

ana

0

50

100

150

200 km

MaturnSub-basin

SanFernando

Orinoco

River

N

Ciudad Bolvar

Rec

lam

atio

nZo

ne

Figure 1.21

Venezuelan petroliferous basins on the basis of its Sedimentary Provinces (after

Prez de Meja et. al., 1980). E. B. L. = El Bal Lineament, Eastern and Barinas-

Apure basins limit.

Northern Venezuela regional

filling of the foreland basins

and uplifting due to the

deformation of extensive

areas associated with the

Bocono, San Sebastin and

Oca fault systems.

Extensional basins persist

north of Falcn State (after

Macellari, 1995.)

To the south of the Gurico Mountain

front, in the Gurico and Maturn Sub-Basins

(including the eastern Interior Mountain

Range), transitional deltaic to shallow-

marine environments are represented by the

Merecure and Oficina Formations (Gurico

and western Anzotegui States). They are

both of great importance as petroleum

reservoirs. These units change gradationally

to the east to deeper-water environments

represented by the Capiricual and Carapita

Formations. The Carapita Formation is a

distinctive turbidite unit and is also of great

petroleum importance.

To the south, in the Oficina fields and

the Orinoco Belt, are found the diachronical

younger equivalents of the Neogene cycle.

The basal unit, usually discordant over the

Temblador Group, is the sandy Merecure

Formation, and overlying it is the deltaic

Oficina Formation. The Miocene equivalents

of these units in the Gurico Sub-

BasinOrinoco Belt have been named the

Chaguaramas Formation.

To the northeast, the Maturn Sub-Basin

is filled with shallower facies, such as the

Uchirito and Quiamare Formations in its

northern flank. The Quiamare Formation

represents a great variety of environments:

lagoon, fluvial channels and alluvial fans,

reaching several kilometers in thickness in

Eastern Anzotegui. On the southern flank,

the Freites Formation shales overlie the

Oficina Formation. These shales are

eventually overlain by the deltaic La Pica

Formation and the molassic Morichito, Las

Piedras and Quiriquire Formations (Pliocene

age). The sedimentary cycle ends with the

Mesa Formation of Pleistocene age.


171

AgePleistocene

Pliocene

LateMiocene

MiddleMiocene

EarlyMiocene

Perij and Lake Maracaibo Andes Barinas-Apure Falcn

GuricoSub-Basin

MaturnSub-Basin

InteriorRange

El Milagro

LA PUERTA (*)

La Villa,Los Ranchos,

Lagunillas

EL FAUSTO/La Rosa

Terrazas

?

Betijoque

Isnot

Palmar

GUAYABO

Parngula

Ro Yuca

Guanapa

San Gregorio/Coro

LA PUERTA/Codore/La Vela/Urumaco/

Caujarao

AGUA SALADA

SocorroCerro Pelado

Castillo/Agua ClaraPedregoso/San Luis

Guacharaca

Chaguaramas

Mesa

Las Piedras

La Pica

Freites

Oficina

MerecureCarapita

Uchirito/Capiricual

Quiamare

(N) (S)

Car

apit

a

Las Piedras/Quiriquire

Reservoir (Sandy)

Sand/Seal Pairs

Seal

Source RockReservoir (Carbonate)

?

?

(*) Group

Figure 1.22

Correlation chart of the

most important units in the

Venezuelan Neogene. (N)

and (S) indicate northern

and southern flanks of the

Maturn Sub-Basin.

The El Fausto Group,

and the Palmar, Guaharaca,

Chaguaramas and Merecure

Formations extend into

Late Oligocene.

Figure 1.23

1 18

The beginningBefore the 1800s, only brief references

were made to Venezuelan hydrocarbons in

the literature. The first mention of hydro-

carbons was made by Fernandez de Oviedo

in 1535, where he wrote of oil seepages off

the western shore of Cubagua Island. In 1540,

he referred to the presence of bitumen on the

Gulf of Venezuela shores (Martnez, 1976).

Nothing more is found in the literature until

the early 1800s.

1800 to 1900 In 1814, Alexander von Humboldt

reported asphalt deposits along Venezuelas

northern shoreline (Martnez, 1976).

Geologist Herman Karsten (1851) published

a description of oil seepage sites located

between Betijoque and Escuque, towns in

Trujillo State, southeast of Lake Maracaibo

(Urbani, 1991).

Oil seeps along La Alquitrana Creek in

Tchira State lured local investors into apply-

ing for an exploitation concession under the

name of Cien Minas de Asfalto. It was

granted to them in 1878 (Martnez, 1976).

Compaa Minera Petrolia del Tchira

exploited this concession by open mining

until 1883, when the first well which

produced oil, Eureka-1, was completed.

Eureka-1 had a production of 1.5 bbl (194

liters) per day (Mndez, 1978). Previously

Salvador-1, the first well drilled in Venezuela,

had been abandoned as dry by this company

after reaching a final depth of 53 m. These

wells were drilled with a percussion rig, the

first oil drilling rig in the country.

1901 to 1920Well locations were chosen by surface

geology and direct hydrocarbon observation

during the first decades of this century.

Bababui-1, a 188-m (617-ft) deep well,

discovered the Guanaco oil field in 1913.

Mene Grande, near Lake Maracaibos eastern

shoreline, was the first giant find in

Venezuela (Fig. 1.25). The discovery well

was Zumaque-1, a 135-m (443-ft) well,

drilled after a recommendation by geologist

Ralph Arnold. Arnold and a team of about 50

colleagues systematically explored more than

50 million hectares assigned to General

Asphalt (later Caribbean Petroleum) all over

Venezuela. Of these, 512,000 hectares were

selected for exploitation. Totumo, discovered

in 1913, was the first producer from the

basement, and La Rosa Field, found by the

well Santa Brbara-1 drilled in 1917, was the

first of a giant later recognized as the Bolvar

Coastal Field (BCF). BCF covers an extensive

land and offshore region on the eastern coast

of Lake Maracaibo. The maximum depth

reached by an exploratory well by 1917 was

1,400 m (4,600 ft).

1921 to 1940From 1920 onward, surface exploration

activity increased (Fig. 1.23). Efforts were

concentrated on Zulia and Falcn States in

western Venezuela, and northern Anzotegui

and Monagas States in Eastern Venezuela.

T H E H I S T O R Y O F O I L E X P L O R A T I O N I N V E N E Z U E L A

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

100

0

200

300

400

500

600

700

Cre

w -

mo

nth

Wo

rld

War

I

Gre

at D

epre

ssio

n

Wo

rld

War

II

Mas

sive

co

nce

ssio

ns

En

d o

f c

on

cess

ion

s

O.P

.E.P

. Fo

un

dat

ion

Nat

ion

aliz

atio

n

Surface geology

Seismic (2-D + 3-D)

Gravimetry (+magnetometryfrom 1936)

Year

Figure 1.23

Exploratory activity in

Venezuela. Surface methods.

(Source: Martnez, 1976 and

1994; M.E.M., 1985 to 1995;

J. Mndez Z., 1976 and R.

Varela, 1987, in Mndez Z.,

1989; M.M.H.,1962 to 1984).

1Pioneering gravimetric surveys started in 1924

and contributed to the identification of

regional highs, mainly of igneous-

metamorphic basement close to the surface.

As a result of the surface exploration effort

and subsequent exploratory drilling during

the 1920s, several important discoveries

occurred: La Paz in 1923, and La Concepcin

in 1925, in Zulia State; Quiriquire in 1928, in

Monagas State (a giant oilfield in a Pliocene

alluvial fan), and Pedernales (Delta Amacuro)

in 1933, in an anticline produced by mud

diapirism. Other relevant discoveries during

this period were the Bachaquero area (now

within BCF, Zulia) in 1930, and Cumarebo

Field (Falcn State) in 1931.

The year 1933 heralded the beginning of

the use of seismic as a surface tool for

exploration (Fig. 1.23), and results were

quickly seen. Large discoveries occurred in

Eastern Venezuela: in 1936, Temblador, the

first field discovered in southern Monagas; in

1937, the first field of the Greater Oficina

Area was discovered in Anzotegui State; and

Jusepn Field was found in northern Monagas

in 1938.

Surface geology continued to render

benefits in Monagas: Santa Ana, the first field

of the Greater Anaco Area, was found in

1936; and El Roble and San Joaqun were

found in 1939. Subsurface geology methods,

using regional knowledge, data from core

and ditch samples obtained during drilling,

and electrical well logging as of 1929, gave

very significant results. Some of the

discoveries include Orocual Field (Monagas)

in 1933, and the Eocene Misoa Formation oil

sands of the LL-370 Area (Lagunillas, BCF,

Lake Maracaibo) discovered in 1938. The

maximum exploratory drilling depth reached

by 1940 was 3,400 m (11,150 ft) (Fig. 1.24).

1941 to 1950The exploratory activity during this

decade was affected by World War II and the

post-war world, with large oil needs

prompting an increase in exploratory drilling

(Fig. 1.24). Surface exploration, however,

diminished, since most of the field personnel

went to war. It was not until the end of

WWII that surface activities showed a strong

upward rebound, reaching levels never

before seen in Venezuela (Fig. 1.23). With an

increase in exploratory drilling after the war,

reserves and production doubled during the

decade (Fig. 1.26), and 63 fields were found.

This compares to the 41 fields found from

1880 to 1940. The three most relevant

discoveries were the Las Mercedes Field

(Gurico State) in 1941, commercial oil in

the Cretaceous of La Paz Field (Zulia State)

in 1944, and the giant accumulation of extra-

heavy crude in Boscn (also in Zulia State),

in 1946.


19

Nu

mb

er o

f ex

plo

rato

ry w

ells

per

yea

r

300

200

100

01910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Maxim

um

dep

ths reach

ed

km

1

2

3

4

5

6

7

Wo

rld

War

I

Gre

at D

epre

ssio

n

Wo

rld

War

II

Massiveconcessions

End ofconcessions

Nationalization

Evaluation ofthe Orinoco

Belt

Year

Figure 1.24

Exploration drilling in Venezuela. (Source: Martnez, 1976 and 1994;

M.E.M., 1985 to 1995; Mndez Z., 1976 and Varela, 1987, Mndez Z.,

1989; M.M.H.,1962 to 1984).

1 20

Exploratory drilling added more fields to

the Greater Areas of Oficina, Anaco and Las

Mercedes. The new Hydrocarbons Law of

1943 provided for the duration of all existing

concessions to be extended 40 more years, a

positive move for the oil industry, although

the states share in exploitation benefits was

increased by way of taxes. In addition,

abundant new concessions were granted

during 1944 and 1945, which also had a

significant positive effect on exploration.

From 1945 on, exploratory evaluation

intensified and all technology on hand was

applied. Gravimetry and seismic surveys

were carried out in areas offshore of Lake

Maracaibo, and aerial magnetics and other

advanced techniques under development

were tested in Venezuela. These tech-

nologies contributed to a significant increase

in the regional knowledge of the Venezuelan

sedimentary basins. Exploration drilling rigs

reached depths of approximately 5,200 m

(17,000 ft), as can be seen in Fig. 1.24.

1951 to 1960The oil from the Middle East, less

expensive and of good quality, affected the

intensity of Venezuelan exploration, and

surface activity was reduced by more than

half (Fig. 1.23). However, drilling activity

maintained a high level during the decade.

New concessions granted in 1956 and 1957

kept the interest in Venezuelan oil high

throughout the rest of this decade.

Discoveries continued in the Greater Oficina

Area and, to a lesser extent, in Gurico.

During 1957 and 1958, the Lake Maracaibo

region yielded large Tertiary finds in its

central and central-eastern areas, including

Ceuta, Centro, Lama, Lamar and Lago Fields.

The first Venezuelan continental platform

find was Posa-112A, an offshore field in the

Gulf of Paria. The maximum exploratory

drilling depth reached during this period

was 5,348 m (17,541 ft).

1961 to 1976The no more concessions policy

adopted by the Venezuelan State greatly

affected the operating strategies of the

concession holders during this pre-

nationalization period. A drastic reduction in

surface exploration activities is shown in Fig.

1.23. By 1968, exploratory drilling reached

the lowest level of activity since 1940.

Exploratory wells were restricted to already

identified areas, with their objectives being

new reservoirs above, below or near known

oil reservoirs. This type of exploration

yielded discoveries such as the deep

Cretaceous in Central Lake and Urdaneta

Fields. Frontier drilling and surface

exploration activities by the concessionaires

ceased completely.


1.500

Millio

ns o

f barrels

Mill

ion

s o

f cu

bic

met

ers

per

yea

r

300

Note: From 1914 to 1954a total of 3.0 billion cubic

meters were incorporated into the reserves through revisions, new

discoveries and extensions.

Men

e G

ran

de

C.C

. Bo

lvar

Los

Bar

roso

s2

La P

azLa

Co

nce

pci

n

Qu

iriq

uir

eB

ach

aqu

ero

Ped

ern

ales

La C

ano

a1

Ofi

cin

aJu

sep

nLa

s M

erce

des

La P

az a

nd

Mar

a (K

)B

osc

nLa

Paz

an

d M

ara

(Bas

emen

t)U

rdan

eta

Lam

a, C

entr

oO

rocu

al,

Lam

ar,

Job

oM

ori

chal

On

ado

Su

r d

el L

ago

Cer

ro N

egro

Pat

aoR

o C

arib

eLo

ran

, co

cuin

aG

uaf

ita

Inco

rpo

rati

on

of

El F

urr

ial

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

200

100

0

1.000

.500

0

Year

Figure 1.25

Reserves from exploratory

drilling in Venezuela.

(Increments and revisions not

included). (Sources: Martnez,

A.R., 1976, 1987 and 1994;

M.E.M., 1985 to 1995;

M.M.H., 1962 to 1984).

The Corporacin Venezolana del

Petrleo (CVP), the Venezuelan State oil

company, was founded in 1960 and started

operations the following year. This company

became the leader in exploration on land

and offshore Venezuela. It acquired 80,000

km of seismic and drilled nearly 200

exploratory wells during this period

(Velarde, 1991). CVP started exploration of

the La Vela area, offshore Falcn State, in

1972, and the evaluation of southern Lake

Maracaibo in 1971 by means of service

contracts. After a bidding process, service

contracts were signed the same year.

A significant discovery during the

period, besides findings in the above-

mentioned La Vela and southern Lake areas,

was Onado Field (1971) in Monagas State.

The exploratory drilling record was 5,813 m

(19,067 ft) in 1976.

CVP and the Ministerio de Minas e

Hidrocarburos started evaluating the Orinoco

Belt by seismic surveys and drilling. By then,

about 60 wells had been drilled by the

concessionaires in the so-called Tar Belt, and

most of them had been abandoned without

testing. The La Canoa 1, a 1,176-m (3857-ft)

deep exploratory well, tested 6 m3 (40 bbl)

per day of 7API gravity before being

abandoned (Martnez, 1987). This well,

located in southern Anzotegui, is

considered to be the discovery well of the

Faja del Orinoco.

1976 (nationalization) to the present

By 1978, state-owned Petrleos de

Venezuela, S.A., a holding in charge of the

nationalized oil industry, assigned the Orinoco

Belt to its existing operating affiliates:

Corpoven, Lagoven, Maraven and Meneven.

They each proceeded to evaluate their

assigned portion. The campaign was finished

five years later (Fig. 1.24) after 669 wells were

drilled, and 15,000 km of Vibroseis seismic

lines and 54,000 km2 of aerial magnetics were

acquired (Martnez, 1987).

Since the nationalization, surface explor-

ation is based almost exclusively on geo-

physics, remote sensing and geochemistry. It

steadily increased until the 1980s (Fig. 1.23),

when it reached its maximum level for the

last 15 years. This activity was directed

toward frontier and traditional areas. 3-D

seismic has been used since the 1980s as an

additional tool for both exploration and

reservoir description.


211

Cu

mu

lati

ve p

rod

uct

ion

an

d r

eser

ves

at y

ear

end

(B

m3 )

5

0

10

BS

TB

70

60

50

40

30

20

10

019201910 1930 1940 1950 1960 1970 1980 1990 2000

Massiveconcessions

O.P.E.P. FoundationEnd of concessions

Production

Reserves

Year

Figure 1.26

Production and reserves in

Venezuela. (Sources:

Martnez, A.R., 1994;

M.E.M., 1985 to 1995;

M.M.H., 1962 to 1984).

1 22

Exploratory objectives have become

deeper and more remote, as the most

significant recent finds show (Fig. 1.25).

These include Patao and other giant gas

fields offshore north of Paria Peninsula (1979

to 1982); Ro Caribe condensate accumu-

lation also in the same region (1981); Morro

heavy oil in the Gulf of Paria (1980), and

Loran and Cocuina, gas accumulations east

of Delta Amacuro (1983) (Fig. 1.0). Northern

Monagas and Anzotegui, both in Eastern

Venezuela, contain the largest discoveries

since 1986 along the El Furrial Trend:

Tertiary and Cretaceous reservoirs that are

more than 4,000 m deep. Western

Venezuelas Guafita and Victoria findings

near the Colombian border are also quite

significant. An exploratory drilling depth

record of 6,640 m (21,780 ft) was set in 1993.

What now?The future points to more discoveries in

the above frontier areas, as well as

exploration and re-exploration in traditional

areas near existing facilities. New, high-risk

objectives will become the standard of day-

to-day exploration activities; exploration for

bypassed hydrocarbons already has high

priority. Modern drilling technology will

allow deeper and more precise subsurface

evaluation. Improved knowledge of

Venezuelan basins, supported by new

geological and geochemical criteria, and

new seismic acquisition and processing

technologies, will open new frontiers and

substantiate re-exploration. Modern

petrophysical well logging technologies,

some of which are described in other

chapters of this book, already permit

measuring and interpreting a large variety of

rock and fluid properties. Their proper use

will further enable us to accurately assess

the subsurface. Venezuela still has a wealth

of hydrocarbons to be discovered. Figure

1.27 displays graphically the exploratory

success during the last 45 years, showing an

almost 47% success rate with no downward

trend, and Fig. 1.26 shows nearly 1 billion

barrels of oil added during the period. This

is the result of integrating all technologies,

from exploration through enhanced oil

recovery. Venezuelan oil provinces have not

yet disclosed all their secrets; only by using

modern exploration technologies will they

be revealed.


0.50

0.48

0.46

0.44

0.42

0.40

0.38

1950 1960 1970 1980 1990 2000

Nu

mb

er o

f d

isco

veri

esTo

tal n

um

ber

of

exp

lora

tory

wel

ls

YearCumulative exploratory

success since 1950, showing

an almost 47% success rate

with no downward trend

(from M.E.M., 1985 to 1995;

M.M.H., 1962 to 1984).

Figure 1.27

1P E T R O L E U M G E O L O G Y O F V E N E Z U E L A

23

Ag

e

Sou

rce

Roc

k

Res

ervo

ir

Sea

l

Form

atio

n

Thic

knes

s (m

)

Mem

ber

Gra

ph

icLi

tho

log

y

Cre

tace

ou

s

A p

n

L i s

u r

e

Maraca

La L

una

M i

s o

a

"C S

and"

"B S

and"

Icotea

La R

osa

L a

g u

n i

l l a

s

Lithological Description

Guasa

re

Col

n/

Mito

Jua

n

T e

r t

i a

r y

Socuy

Bac

haqu

ero

300-

900

250

1000

-160

0

120-445

900

100-

300

120

55-1

8050

0-60

0m

RoNegro

Shales, claystone, weakly consolidatedsandstones, and some interstratified lignites.

50-180

Lagu

na

Lowe

r

Guim.

Pic

h

Tib

Sta.Brbara

Middle

Upper Marine shales with iron-rich concretions;variable amounts of interstratifiedsandstones.

Siltstones, hard shales/mudstones andsandstones.

Intercalation of sandstones, siltstones and some limestone layers in the lower part.

Fossiliferous limestones and calcareoussandstones.Dark and massive microfossiliferous shales, with some thin sandstones and limestone layers.Fetid calcareous limestones and shales,elliptical concretions.

Crystalline limestones with Ostrea Sp., with shale and marl intercalations.

Glauconitic sandstones and sandy limestones, with sandy laminated mud intercalations, and some shelly limestone layers.

Fossiliferous massive limestones, nodular, marly and often calcareous shales.

White coarse-grained sandstones.

1 24

Maracaibo BasinThe Maracaibo Basin (Fig. 1.21) is the

most important petroliferous basin of Vene-

zuela. The main source rock is the La Luna

Formation (Figs. 1.28 and 1.29) of Late Creta-

ceous age; its facies extend along all of

Western Venezuela and Colombia. There are

some other source rocks of secondary import-

ance in the Cogollo (Machiques Member of the

Apn Formation) and Orocu (Los Cuervos

Formation) Groups. The oil was generated,

migrated and accumulated in several phases,

the Andean uplift being the most important

one. These points will be elaborated later.

The main clastic reservoirs are the Ro

Negro and Aguardiente Formations (Creta-

ceous), Orocu Group (Paleocene), Mirador-

Misoa (Eocene), Lagunillas and La Rosa

Formations (Miocene) (see the stratigraphic

columns in Figs. 1.28Perij/Lake Maracaibo

and 1.29North-Andean Flank). The

outstanding carbonate reservoirs belong to the

Cogollo Group (Early Cretaceous). The most

important regional seals are the Coln (Late

Cretaceous) and Pauj (Eocene) Formations.

P E T R O L E U M B A S I N S M A R A C A I B O

E

0

1

2

3

4

5

6

1.8 Km

La VillaLos Ranchos

PerijRange

Miocene

Paleocene

El Fausto

W

10 km

Post-Miocene

Icotea High Lagunillas

Bachaquero Fault

TrujilloRange

La PuertaLagunillas

La Rosa

Pauj

Trujillo

Misoa

Eocene

Jura

ssic

Shaly (Seal)

Sandy / Conglomeratic

Carbonate

Source Rock

Sand/Seal Pairs

Urdaeta

Cretaceous

"B"

"C"

"B"

"C"

Lama

Two

way

tim

e (

sec)

Basement

Misoa

Geological timescale

Petroleumsystem events

Formations

Source rock

Seal

Reservoir

Burial

Trap formationGeneration,migration,

accumulationPreservation

Critical moment

200 150 100 70 60 50 40 30 20 10 0

QCenozoic

MioceneOlig.EocenePaleo.Tertiary

MesozoicTr JL E M L E

KL PP

(Ma)

Note: The sequence ofevents in the petroleumevents system is asfollows: the sedimentaryrecord is indicated in therow named "Formations;"in this case there is sed-iment preservation bet-ween the Early Creta-ceous and the Late Pa-leocene, followed by a 5to 6 Ma hiatus; thenthere are sedimentspreserved between theEarly Eocene and the Eo-cene-Oligocene limit.The source rock is gen-erated at the end of theEarly and part of the LateCretaceous. The seal isdeposited at the end ofthe Late Cretaceous andEocene times. Reservoirrocks are depositedduring the Late Creta-ceous and Eocene. Thesource rock in this

system (La Luna For-mation) is buried duringLate Cretaceous, andpartially unloaded bet-ween the Late Paleoceneand Early Eocene; burialcontinues during the restof the Eocene. Strati-graphic and structuraltraps are formed bet-ween the Late Creta-ceous, Paleocene andLate Eocene. The gener-ation, migration andaccumulation from thesource rock for this sys-tem takes place duringLate Eocene, and thepreservation of the trapstakes place since theOligocene. So the criticalmoment, or the timewhen there is the max-imum probability for oilentrapment and pre-servation, is the Eocene-Oligocene limit.

"Phase 1" petroleum system, Maracaibo Basin (after Talukdar and Marcano, 1994).

East-West Maracaibo

Basin section (after

Parnaud et al., 1995).

Figure 1.30

Figure 1.31

1Locally, the Machiques Member (Apn

Formation) is a good seal, as well as the

thick interstratified shale intervals of the

reservoirs toward the center of Lake

Maracaibo, such as Misoa, Lagunillas and La

Rosa (Fig. 1.30Lake Maracaibo EW

section). Other good seals include the shaly

Len Formation and some thick intervals of

the molasse (Guayabo and El Fausto Groups;

Andes and Perij, respectively).

The main oil fields are located on the

Eastern Coast of Lake Maracaibo and the

main production comes from Tertiary

reservoirs; for example, Cabimas, Ta Juana,

Lagunillas, Bachaquero, Mene Grande and

Motatn. On the west coast there are fields

with production from the Cretaceous and

even Tertiary; for example, Urdaneta (Lake

Maracaibo) and several fields of the Perij

foothills, such as La Concepcin, Mara, La

Paz, Boscn and Alturitas. In the central part

of the lake, fields are located along the fault

systems of Lama-Icotea (Fig. 1.30), including

the Lago, Centro, Lama and Lamar Fields.

The oil gravity is quite diverse. In

general, the lighter types occur in the deep

Cretaceous reservoirs, becoming heavier as

depths get shallower. In the upper Tertiary

reservoirs of the lakes Eastern Coast, some

of the oils have gravities less than 13API.

Petroleum Systems

Figures 1.31 and 1.32 represent the

northeast Lake Maracaibo petroleum system

generated by the La Luna Formation source

rocks. Oil generation occurs in the northeast

part of the basin, with migration and

accumulation in the southwest during the

Late Eocene. The main traps occur along the

Icotea high, containing Cretaceous and

Eocene reservoirs. The highest probabilities

of accumulation, or critical moment, is

found close to the Oligocene-Eocene

boundary (Fig. 1.31).


25

8

Oca Fault

Lake Maracaibo

Colo

mbi

a

Perij

Ra

nge

Gulf of Venezuela

Trujillo Range

FalcnBasin

Vene

zuela

n And

es

N

0 km 50

Oil Field, Eocene Reservoir

La Luna System Limit (Phase 1)

Maracaibo Basin Limit

La Luna Source Rock Matured or Over-Matured during the Phase 1 (38 My)

Figure 1.32

Defined petroleum system in the Maracaibo Basin, La Luna Formation source rock,

Phase 1 (38 Ma) (after Talukdar and Marcano, 1994).

Geologic timescale

Petroleumsystem events

Formations

Source rock

Seal

Reservoir

Burial

Trap formationGeneration,migration,

accumulationPreservation

Critical moment

200 150 100 70 60 50 40 30 20 10 0

QCenozoic

MioceneOlig.EocenePaleo.

MesozoicTr JL E M L E

KL PP

Tertiary

(Ma)

"Phase 2" petroleum system; Maracaibo Basin (after Talukdar and Marcano, 1994).

Figure 1.33

1 26

Another system results from the

Cretaceous source rock (mainly La Luna

Formation), but in this case it is widespread

across the hydrographic basin of Lake

Maracaibo (Fig. 1.33), reaching over-maturity

conditions in some areas. Generation,

migration and accumulation occurred during

the

cha 1

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