sequence stratigraphic and structural interpretation and ...€¦ · sequence stratigraphic and...

Sequence Stratigraphic and Structural Interpretation and Modeling in the National Petroleum Reserve in Alaska (NPRA)

Lauren SchultzAdvisor: Prof. Chris ConnorsWashington and Lee Department of Geology

Objectives of Study

• Generate a regional interpretation for significant strata in the North Slope of Alaska using geophysical data

• Gain insight into the stratigraphic and tectonic history of the region, e. g. what is the relationship between major sequence boundaries and later thrusting?

• Create a balanced model of the region to account for observed stratigraphy and structure

Potential Applications

• Significant petroleum production in the North Slope- Prudhoe Bay, Alpine etc.

• Understanding of stratigraphy, structure and relative timing is very relevant to petroleum exploration– Source rock depositional environment

– Reservoir facies, i.e. shelf or deep water versus slope

– Structural traps

Prudhoe Bay

Alpine Oil FieldTarn Oil Field

National Petroleum Reserve in Alaska

• Region set aside by Congress for the exploration and production of oil and gas.

• Previous studies:– USGS undertook a comprehensive

study of the region in 70’s-80’s, including drilling test wells and collecting 14,000+ miles of geophysical survey data (Gryc, 1988)

– Sequence stratigraphic interpretation of Cretaceous section: Houseknecht et al. 2009, Houseknecht and Bird, 2004, also theses by W&L geo students Stier (2012), and (in the state lands) Frierson (2011)

– Fault-related folding interpretation of the state lands: thesis by W&L geo student Stockmeyer (2011).

• Bill pending in congress to commission a new USGS study of the region (H.R. 2150)

DEM from ASTER GDEM

Study Area

Data

-USGS NPRA R-Lines (~8000 line km)-Well tops and logs (~275 wells) and access to other seismic lines in the region ~200,000 line km)

Work Flow

• Formation tops from well logs correlated to seismic data

– Time to Depth functions generated

• Stratigraphic sequences interpreted across study area

• Structural interpretation of the fold and thrust belt to the South

• Velocity Model and Depth Conversion

• Create 3D model of horizons and structures

Regional StratigraphyNanushuk & Torok – Clinoform depositional sequences composed of dark marine shales and sandstones associated with the Chukotka orogenic belt which shed sediment eastward (Middle Cretaceous)

Pebble Shale – A thin organic rich black shale that lies unconformably on the Kingak Shale (Early Cretaceous)

Kingak – Deposited in a succession of sequences during the rift opening of the Arctic Ocean (Late Triassic to Early Cretaceous)

Shublik – A mixture of carbonate, mudstone, shale, and sandstone depostited on a southward sloping margin, representing a regional marine transgression (Triassic)

(Stier, 2012; Houseknecht et al., 2009; Houseknecht and Bird, 2011; Houseknecht and Bird, 2009, More et al., 1994)

Modified from Houseknecht and Bird, 2009

Nanushuk & Torok

http://www.aapg.org/explorer/2010/12dec/alaska1210.cfm

• Lithostratigraphic versus Chronostratigraphichorizons

• Nanushuk is predominantly sands = shelf facies• Torok is predominantly shale = slope facies• Mapping of time horizons rather than of a rock

type/facies

Mitchum, 1977

-Relationships between sequences are previously established, as per Mitchum, 1977-Use these relationships between strata to identify sequence boundaries

VE=10:1

1

2

SL

3

10 km

NPRA Line R-14

VE=10:1VE=10:1

1

2

SL

3

10 km

NPRA Line R-14

VE=10:1VE=10:1VE=10:1

1

2

SL

3

10 km

NPRA Line R-14

T1T2T3T4

VE=10:1

1

2

SL

3

10 km

NPRA Line R-14

Torok2 Horizon Surface-Surface interpolated from horizon picks on seismic lines-Contour interval = 0.1 sec

Shelf Margin

Structure Contour Map of T2

0

1

2

100 km

100 km

0.5

0

Isopach Maps between Torok Seq. T3-T4Isopach (isochron) =Thickness Map

=Difference in time between two mapped horizons

100 km

Max

Min

Progradation of Shelf Margin, Torok Seq. T3-T4 Isopach

100 km

Max

Min


Torok Shelf Margin

• Torok shelf margin moves eastward through time

• Eastward shift is result of progradation of Torok clinoformsequences

Structural Interpretation

VE=1:1

10 km

10 km

R-21

Structural Interpretation10 km

VE: 4:1

VE: 4:1R-4

R-21

Structural Interpretation

VE=10:1

10 km

R-16

Depth Conversion

• Seismic data is in time units, so horizons are also in time units

• Horizons and faults must be converted to depth in order to build a model in depth units

– Associate well data (depth) to interpreted horizons (time) in order to build a velocity model over the NPRA

– Velocity model can then be used to convert time horizons into depth

Sample Average Velocity Surface: Torok

Sample Average Velocity Surface: Shublik

Sample Depth Converted Section

E

• Pink layer is Shublik Formation top• Shublik was relatively flat lying upon deposition, later

tectonically uplifted in North

• Green layers are Kingak shale• Progradation from North to South

• Orange layer is Pebble Shale/GRZ• “Drape layer” – continuous sediment drape across region due

to sea level high

• Blue layers are Torok Formation• Progradation from West to East• Torok fills accomodation created by Kingak shelf margin and

foreland of ancestral Brooks Range

• Blue layers are Torok Formation• Progradation from West to East• Torok fills accomodation space created by Kingak shelf margin

and foreland of ancestral Brooks Range

• Blue layers are Torok Formation• Progradation from West to East• Torok fills accomodation space created by Kingak shelf margin

and foreland of ancestral Brooks Range• Top Torok layers have been eroded post-deposition in central

NPRA

Conclusions

• Sequence stratigraphic interpretation shows progradational clinoforms in Torok sequences

– Sequence geometry evolves over time

– Shelf margin progrades eastward

• Structural interpretation is consistent with typical fold and thrust belt deformation

– Fault-related folding

– Detachments in weaker shale layers

• Lower detachment in condensed shale section (Shublik, Kingak, Pebble Shale)

• Upper detachment in Torok slope facies

Future Work

• Restoration of models in 3D and cross sections in 2D

– Undo structural deformation, i.e. faulting and folding

– Decompaction to remove burial effects

• Basin modeling

• Connect interpretation here with previous work in adjacent regions

Acknowledgements

Thanks to:

• Chris Connors, Department of Geology

• Dave Houseknecht, USGS

• R E Lee Summer Research Grant

• Washington & Lee Department of Geology

• Natalie Stier ‘12, Allen Frierson ‘11, Joe Stockmeyer ‘11

Los Angeles Basin: Potential Future Work at Stanford

Background

• Strike-slip basin, formed in Neogene (Wright, 1991)

• Very petroliferous relative to sediment fill volume (Peters, 2013)

– Several distinct petroleum families identified within the basin (Peters, 2013)

F’

F

>12,000 ft

Family

11, 12, 13

21, 22

31, 32, 33

41, 42

5

6

From Wright (1991), Peters (2013)

A

A’

PALOS VERDES

HILLS

Figure 1. Map of the Los Angeles basin shows depth contours on base Mohnian (~14 Ma; Late

Middle Miocene) >12,000 ft in pink. NIFZ = Newport-Inglewood Fault Zone, tribes 1-2 = green,

tribes 3-6 = red.

Los Angeles Basin: Potential Future Work at Stanford

Goals of Project

• Create 3D Petromod model of L.A. Basin

• Incorporate subsurface data, including formation tops, ages, lithology, TOC, etc. and calibration data, including pressures, temperatures and vitrinite reflectance

• Run kinetics on thermally immature source rock equivalents

54Basin and Petroleum System Modeling Industrial Affiliates Program

sequence stratigraphic and structural interpretation and ...€¦ · sequence stratigraphic and...

Documents