wellsite geology

1/184 WELLSITE GEOLOGY

Cuttings Logging

Oil show evaluation (Fluorescence )

Drilling Core Logging

Side Wall Core Logging

WELLSITE GEOLOGY


Cuttings Logging


Cuttings

• Cuttings are rock fragments broken from the penetrated rock during drilling operations.

• Characteristics– Some cuttings have sign cut by the bit.– Mix

• Direct material of formation


Real Cuttings & False cuttings

• Real cuttingsCuttings coming from bit penetrate to open new hole.Brilliant colorsmaller size (2-5 mm, effected by formation hardness, bit tooth shape and size)Poor roundness ( considering hardness and consolidate extent)

• False cuttings (Caving) dull color, bigger size, sorted cuttings


Sampling and Cuttings Analysis

• Reasons for sample collection and shipping

• Sample Intervals

• Sample Types

• Sample collection and preparation

• Cuttings examination

• Sample description


Reasons For Sample Collection and Shipping

• Wellsite geological information

• Paleontological / Palynological analysis

• Geochemical analysis

• Oil company partners

• Governmental requirements

• Future reference / library samples


Sample Intervals• Set by the client, named in well proposal.• Common intervals: 10m, 5m, 2m, 1m.• Regardless of the sampling interval, under no

circumstances should the mudlogger neglect their other responsibilities

• Other times that the sample interval should be shortened:– During coring – 1 ft or 0.5 meter intervals– Areas of geological interest– Changes in drilling parameters (drill breaks / reverse drill breaks,

torque changes)– Changes in mud properties (viscosity, cut MW, chlorides, etc)– Changes in gas content


Sample Types

• Wet unwashed samples

• Washed and dried samples

• Geochemical samples

• Paleontological / Palynological samples ( biostrat sample)

• Metal shavings

• Mud samples


Sample Collection• Install a sample collection basin at the base of the shaker• Try to collect from the shaker with the smallest mesh size• Samples are taken at regular intervals specified by the

client• Samples should be taken when changes in ROP,

background gas or any other parameter is noticed. (spot sample, for casing point, coring point, formation tops, gas show, required by geologist or company man)

• Regularly check desander and desilter for samples• When sampling in smaller intervals than required, the

sample bags should be progressively filled up• Clean the sample board after a sample is taken


Sample Catching Board


Sample Preparation• In clayey areas, care must be taken to wash away as

little of the clay as possible.• When determining the sample composition, take into

account any clay that may have been washed away• Samples are washed through at least 2 sieves (80 or

120 mesh at the bottom and 8 mesh on top)• Cuttings left on the 8 mesh sieve are considered to be

cavings• A sample of these cavings should be placed on the

sample tray for observation


Cavings• Cavings are cuttings from

previously drilled intervals• Most removed by the coarse

seive• Generally be recognized as

large, splintery rock fragments that are concave or convex in cross-section

• Lithologically identical with formations from higher sections in the open hole


Importance of Cavings

• An increase in the amount of cavings this could indicate an unstable hole

• Cavings with splintery, concave appearance may indicate increasing formation pressure

• If the cavings are of the same lithology, then by reviewing the master log, areas of washouts or hole problems can be pinpointed

• Much cavings found should be reported to wellsite geologist and company man.


Preparing Samples Where Oil Based Mud Is Used

1. Fill 2 containers with base drilling fluid (e.g. diesel if mud is diesel-based)

2. Immerse sample in Bath A (initial bath) and sieve sample3. Immerse sample in 80 mesh in Bath B (final bath)4. Take a representative sample to be examined under the

microscope; leave the sieves outside of the unit5. Use a detergent degreaser to wash the sample and then rinse

with water• NOTE: All OBM samples should be air dried outside the

logging unit• Use rubber gloves when handling OBM samples


Cuttings Examination

• Samples are examined under the microscope for:– Lithology– Oil staining– Porosity

• Objective:– To depict changes of lithology and appearance

of new formations


Sources of Sample Contamination

• Cavings

• Recycled cuttings

• Mud chemicals

• Cement

• Metal

• Unrepresentative samples


Cases Where Unrepresentative Samples Occur

• Evaporite sections drilled with water-based muds

• Drilling soft clays/shales

• “Rock flour” due to high speed drilling

• “Burning” of cuttings while drilling with diamond bits


End of Topic


Functions and Format

Sample Description


Sample Description

• Major functions

• Porosity and Permeability

• Description format

• Describing clastic rocks

• Describing carbonate rocks

• Describing other chemical rocks

• Describing igneous and metamorphic rocks


Major Functions of Sample Description

• Allows another person to understand the components and structure of the rock and to draw conclusions as to the source, depositional environment and subsequent history of the formation

• Allows another person to recognize the rock whenever it is seen again


Porosity and Permeability

• Porosity is a measure of the volume of void space in the rock. It determines the amount of fluid that is present in a rock.

• Permeability is a measure of the capacity of a rock for transmitting fluid and it is dependent on effective porosity and the mean size of the individual pore spaces. It has a direct bearing on the amount of fluid that can be recovered.


Sample Description Format1. Rock type / Classification2. Color3. Texture: Cuttings shape and parting (calcareous and

argillaceous lithologies), Grain size, Grain shape or roundness, Sorting, Hardness or induration, Luster / Slaking / Swelling

4. Cementation or matrix5. Fossils and accessories6. Visual structures7. Visual porosity8. Oil show descriptions


Sample Description Examples

• Sst: lithic, lt gy-off wh, vf-f gr, occ med gr, sbang-sbrd, mod w srtd, fri, sl arg mtx, v wk calc cmt, mica, glau, p-fr vis por, tr-5% blu wh fluor, slow strmg bl wh cut, no cut color, no res, p oil show.

• CLYST: lt gy-med gy, occ dk gy, sbblky-blky, mod hd, mic mica, sl calc.

• Ls: oolitic grainstone, buff-brn, med gr, mod hd, arg, Brach, glau, gd vis por, no oil show


Rock Type

Consists of two fundamental parts:

• Basic rock name (Sandstone, claystone)• Proper compositional or textural classification

term (lithic, quartzose, oolitic grainstone)


Color• Rock color may be due:

– Mass effect of the colors of its constituent grains– Cement or matrix color– Staining of cement or matrix

• Use a rock color chart for standardization of color• Observe samples when they are wet• Dried cuttings may be viewed to allow a better

discrimination of subtle hues and color shades• When describing color, distinguish between rock

particles, staining, matrix/cement and accessories


Color

• Rock color may occur in combination or in patterns

• Suitable descriptions are:– Mottled Banded Spotted– Variegated Multicolored Speckled– Iridescent Scattered


Color: Depositional Environment

Color Depositional Environment

Red and brown Oxidizing environment

Green & grey Reducing environment

Dark brown Possible source rock

Black Anaerobic environment


Texture

• Texture refers to the physical makeup of rock-namely, the size, shape, and arrangement (packing and orientation) of the discrete grains or particles of a sedimentary rock


Cuttings Shape

• Blocky• Subblocky• Amorphous• Elongate• Flat or Tabular• Platy• Irregular

• Splintery


Parting (Shales)

• The mud logger should always distinguish between shale, which exhibits parting or fissility, and mudstone or claystone, which yields fragments, which do not have parallel plane faces.


Grain Size

• Grain size and sorting have a direct bearing on porosity and permeability

• Size classifications are based on the Wentworth scale

• Report weighted average• If largest grains present are much larger than the

average, the maximum size should be reported• If the grain size range is large and diverse, report

the minimum to maximum size (e.g. vf – vc)• Use Grain Size comparator chart


Grain Shape

• A function of roundness and sphericity

• Use Grain Shape comparator chart

• Gives clues to:– Mode and distance of transport– Porosity and permeability


Sphericity

• Sphericity refers to the comparison of the surface area of a sphere of the same volume as the grain, with the surface area of the grain itself.


Roundness

• Roundness refers to the sharpness of the edges and corners of a fragment or grain.

• 5 degrees of roundness:– Angular– Subangular– Subrounded– Rounded– Well rounded


Particle Shape: Roundness vs. Sphericity


Supplemental Grain Shape Descriptive Terms

Sharp Elongate Bladed

Flat Rod-like Blocky

Platy Conchoidal Irregular

Disk Faceted Fibrous


Sorting• Sorting is the measure of dispersion of the size

frequency distribution of grains in a sediment or rock. It involves shape, roundness, specific gravity, mineral composition and size.

• Along with Grain Size both have a direct bearing on porosity and permeability

• Most difficult and subjective assessment• A function of mean grain size• If more than 50% of the cuttings are of the same

modal size, the sample is well sorted


Sorting


Hardness and Induration

• Hardness is a physical parameter based on the amount of force required to break apart the cutting using a simple probe

• Induration is the process by which a sediment is converted into a sedimentary rock. It is function of the type and quantity of the cement


Hardness: Descriptive Terms

Soluble Soft Firm

Plastic Unconsolidated Friable

Moderately Hard Hard Very Hard

Brittle Loose Dense

Crumbly


Luster

• Describes the surface features of a cutting under reflected light

• Observe features with naked eye and under microscope and when wet and dry

• Rotating the sample tray under the light source also helps in describing luster


Luster: Descriptive Terms

• Coated

• Vitreous, glassy, faceted

• Silky, pearly (nacreous), polished

• Frosted, dull, etched

• Pitted

• Striated


Slaking and Swelling

• Marked slaking and swelling in water is characteristic of montmorillonite (a major constituent of bentonites) and distinguishes them from kaolins and illites

• Add water to dried cuttings


Slaking and Swelling

• Non-swelling – doesn’t break up in water even after adding 1% HCl

• Hygroturgid – swelling in a random manner• Hygroclastic – swelling with irregular pieces• Hygrofissile – swelling into flakes• Cryptofissile – swelling into flakes only after

adding 1% HCl


Relationship Between Texture, Porosity and Permeability

• Porosity (and possibly permeability) may decrease with increased sphericity and rounded grains.

• Permeability decreases with decreasing grain size because pore throats are smaller and the capillary pressure goes up.


Matrix

• Matrix consists of small individual grains that fill interstices between the larger grains.

• In general, where intergranular contact does not occur, the fill material between grains is matrix.

• Matrix material does have cementing qualities which holds the grains fixed relative to each other.


Matrix Materials

• Silt acts as a matrix, hastening cementation by filling interstices

• Clay is a common matrix material


Cement

• Cement is a chemical precipitate deposited around the grains and in the interstices of a sediment as aggregates of crystals or as growths on grains of the same composition.

• It may be derived from, or related to, the rock particles, matrix, or can externally derived.


Cementing Agents• Common cementing agents:

– Calcite (most common)– Silica (most common)– Sulfates (Gypsum, Anhydrite)– Clays– Dolomite

• Minor cementing agents:– Siderite– Fe oxides– Pyrite– Zeolites– Phosphatic minerals


Cementing Agents: Sandstones

• Chemical cement is uncommon in sandstone that has an argillaceous matrix.

• Silica cement is common in nearly all quartz sandstones usu. as secondary overgrowths.

• Dolomite and calcite are deposited as crystals in the interstices and as aggregates in voids. (Note: both could also be found as detrital grains)


Cementing Agents: Sulfate Cements

• Anhydrite and gypsum cements are more commonly associated with dolomite and silica than with calcite


Cement or Matrix• Cement is deposited chemically and matrix

is deposited mechanically.


Fossils and Accessories

• Minerals or fossils in trace quantities

• Have great diagnostic and descriptive value

• If the accessory mineral could not be identified it should be carefully described


Fossils

• Used for correlation

• Common fossils and microfossils encountered are: foraminifera, ostracods, bryozoa, corals, algae, crinoids, brachiopods, pelecypods and gastropods

• Presence and abundance should be recorded


Fossils: Estimation of Abundance

> 25% Abundant

10% – 25% Common

< 10% Trace


Common Accessories

• Glauconite• Pyrite• Feldspar• Mica• Siderite• Carbonaceous material• Heavy minerals• Chert• Lithic fragments


Crystal Structure Terminology

• Anhedral - no visible crystal form

• Subhedral - partly developed crystal form

• Euhedral - well developed crystal form


Visual Structures• Most sedimentary structures are not discernible in

sample cuttings• Structures in individual cuttings may be

indiscernible• Slickensided surfaces should be carefully

scrutinized• Other structural types, which may be visible in

cuttings, are:– Fractures (usu. w/ some type of fillings),

jointing/partings, bioturbidation, lamination


Visual Porosity

• Easier to determine with a dry sample than on a wet one

• A magnification of 10x is frequently adequate to establish the amount of relative visible porosity in a dry sample.

• Samples with good porosity should always be examined for hydrocarbon shows

• The porosity in rudaceous and arenaceous rocks is primarily interparticle


End of Topic


Sample Description:

Clastic Rocks


Clastic Rocks: Rock Type

Rock size Consolidated Unconsolidated

Rudaceous Conglomerate

Breccia

Tillite

Gravel

Scree

Till

Arenaceous Sandstone

Siltstone

Sand

Silt

Argillaceous Claystone

Shale

Clay

Clay / Mud


Clastic Rocks: Classification

• Sandstones:– Orthoquartzite (Qtz >75%, qtz cement)

– Greywacke (badly sorted, Qtz <75%, lithic frags > feldspars)

– Arkose (coarse qtz and feldspars in a calcitic or ferruginous cement, Qtz <75%, feldspar > lithic frags)

• Claystone / Shale:– Difference between claystone and shale is fissility


Clastic Rocks: Hardness and Induration

• Common descriptions are:– Rudaceous and arenaceous rocks:

unconsolidated, friable, moderately hard, hard and extremely or very hard

– Argillaceous rocks:

soluble, soft, plastic, firm, hard– Other descriptive terms:

brittle, dense, crumbly, loose, amorphous


Hardness and Induration: Arenaceous Rocks: Definitions

• Unconsolidated – cuttings fall apart or occur as individual grains

• Friable – rock crumbles with light pressure; grains detach easily with a sample probe

• Moderately hard – cuttings can be broken with some pressure

• Hard – grains difficult to detach; extreme pressure causes cuttings to break between grains

• Extremely hard – grains can’t be detached; cuttings will break through the grains


Hardness and Induration: Argillaceous Rocks: Definitions

• Soluble – readily dispersed by running water• Soft – no shape or strength• Plastic – easily molded and holds shape; difficult

to wash through a sieve• Firm – material has definite structure and shape;

readily penetrated and broken by a probe• Hard – sharp angular edges; not easily broken by a

probe


Clastic Rocks: Luster

• Common terms used:– Coated, vitreous, glassy, faceted, silky, pearly

(nacreous), polished, frosted, dull, etched, pitted, striated

• Common terms used for argillaceous rocks:– Earthy, silky, waxy, velvety, soapy, resinous


Clastic Rocks: Visual Porosity

• 3 types of porosity: interparticle, moldic, fracture• The porosity in rudaceous and arenaceous rocks is

primarily interparticle or intergranular• The theoretical maximum porosity for a clastic

rock is about 26%.• Never use numerical values in estimating porosity,

use descriptive terms


Visual Porosity Table for Clastic Rocks

Porosity Descriptive term

>15% Good

10% to 15% Fair

5% to 10% Poor

<5% Trace


End of Topic


Sample Description:

Carbonate Rocks


Describing Carbonate Rocks

• Carbonate rocks are difficult to classify because of the complexity of sources and types of their occurrences


Carbonate Rocks: Rock Type

Rock Type Reactivity in 10% HCl

Limestone Reacts instantly and violently

It will float on top of acid

Dissolve within minutes

Dolomitic Limestone Reacts immediately

Reaction is moderate but continuous

Move about in acid

Calcitic Dolomite Reacts slowly and weakly at first,but accelerates to a continuous reaction after a few minutes

Some bobbing up and down

Dolomite Very slow and hesitant reaction

Bubbles evolve one at a time

Leave acid milky


Aids to Carbonate Rock Determination

• Calcimeter

• Alizarin Red– Limestone will turn deep red– Dolomite is unaffected


Dunham Classification System

Rock Type Description

Mudstone (Mdst) Composed of lime mud and <10% grains. Mud supported.

Wackestone (Wkst) Composed of lime mud with >10% grains. Mud supported.

Packstone (Pkst) Composed of grains. >10% interstitial mud matrix and occasionally sparry calcite or pore space. Grain supported.

Grainstone (Grst) Composed of grains. <10% interstitial mud matrix. Grain supported.

Boundstone (Bdst) Original constituents are bound together and supported in place by organic growth.

Crystalline (Xln) All original textures gone because of recrystallization. Distinct crystal faces with occasional relics.


Dunham: Mudstone


Dunham: Wackestone


Dunham: Packstone


Dunham: Grainstone


Dunham: Boundstone


Carbonate Rocks: Color

• Of less importance than in clastics

• Variations in color may be the result of the presence of detrital material (clay) or from the substitution of metallic ions into the mineral lattice

• Describe color when sample is wet


Carbonate Rocks: Grain Size

• Describe the size of physically transported particles (oolites, interclasts, fossils, pellets) and chemically precipitated minerals (either as pore-filling cement, primary ooze, or products of recrystallization and replacement)


Carbonate Rocks: Grain Shape

• Terminology used for clastic rocks may be used


Grain Type Categories

Grain Type Example

Detrital Grains Rock fragments, intraclasts

Skeletal Grains Crinoidal, Molluscan, Algal

Pellets Fecal Pellets, grains of mud

Lumps Composite grains, Algal lumps

Coated Grains Oolites, Pisolites, Encrusted grains


Carbonate Rocks: Sorting

• Sorting in carbonates (as in clastics) is a function of mean grain size

• Very little is known about carbonate sorting because of the varied grain types found in carbonate rocks

• To describe sorting in carbonates, two conditions must be met:– Particles of diverse kinds and/or sizes are present in a

sequence of samples– These particles are segregated into layers of varying mean

grain size


Carbonate Rocks: Hardness or Induration

• Same as those for clastics


Carbonate Rocks: Luster

• The significance and terminology is the same as used for clastic rocks

• Additional terms that are used:– Rhombic, Sucrosic, Microsucrosic, Grainy,

Oolitic

• Use combinations where applicable


Carbonate Rocks: Cement or Matrix

• Cementation is a result of crystallization from an aqueous solution with unimpeded growth into a void

• Lime mud/clay matrix is an integral part of the deposited sediment

• Matrix recrystallization occurs at the lattice level in the solid phase


Carbonate Rocks: Cement or Matrix

• It is not recommended that such terms as weakly and strongly be used. Preferably use the terms: partially, poorly, moderately, well, very well, extremely well for intergranular cement and pressure recrystallization at grain boundaries

• If recrystallization occurs across grain boundaries, resulting in a total crystalline structure, the term “cement” should not be used


Micrite and Sparite

• Micrite – abbreviation of “microcrystalline ooze”; a precipitate formed within the basin of deformation and showing no or little evidence of transport; consists of crystals 1-4 μm diameter occuring as matrix (dull and opaque ultra fine-grained material that forms the bulk of limestones and the matrix of chalk)

• Sparite cement consists of clean calcite crystals, generally longer than micrite, forming pore filling cement between grains and within cavities


Carbonate Rocks: Accessories or Inclusions

• Minor accessories – detrital or diagenetic products of terrigenous rock fragments with some mixed carbonate terrigenous diagenetic minerals

• Elemental sulfur and metallic sulfides (as concretions or staining on fractures) is common

• Silica (chalcedony, chert and crystalline quartz)• Fossils


Carbonate Rocks: Visual Structure

• Most significant structural features are postlithification voids (fractures, fissures, joints, vugs) because they have a major impact on rock strength, porosity and permeability and are significant in terms of reservoir potential and lost circulation problems

• Other less prominent features: slickensides and staining


Carbonate Rocks: Visual Porosity

• Pore size can vary from one micron to hundreds of meters

• The simplest and most common classification of porosity is primary and secondary


Porosity Classification of Carbonate Rocks

• Intergranular – pore space between grains or particles of a rock

• Intercrystal – pore space between crystals of a rock

• Vuggy – pore space between grains or crystals of a rock wherein the space is equal or larger than the size of the individual grains or crystals. It usually has the form of irregular voids.

• Moldic – due to the leaching of soluble grains• Fracture


Carbonate Rocks: Primary Porosity

• Primary porosity is porosity formed as an integral part of the rock fabric. – Ex: interparticle porosity and voids within

skeletal particles and growth structures


Carbonate Rocks: Secondary Porosity

• Secondary porosity is porosity formed secondary to the rock fabric. This type is usually not seen in cuttings, but may be inferred.– Ex: fractures, fissures, vugs


Chalky

• A widely used surface-texture term denoting dull and earthy in many calcareous rocks

• Can also be applied as a porosity term


End of Topic


Sample Description:

Chemical Rocks


Chemical Rocks

• Chert

• Halite

• Anhydrite and Gypsum

• Carbonaceous rocks


Chemical Rocks: Chert

• Very hard (very slow ROP, bit bouncing, vibration)• Glass-like brittleness• Bedded cherts are usually even bedded, thinly

laminated to massive• Color could be indicative of the environment of depos

ition• Cuttings: large, elongate, blade-shaped, fresh

conchoidal fracture surfaces, cryptocrystalline or microcrystalline, very hard

• Possible abundant metal shavings in the sample


Chemical Rocks: Chert Color

• Diatomaceous and radiolarian chert is black to dark grey due to clay impurities

• Spiculiferous cherts are light to medium grey with a brown to green tinge due to large amounts of calcite


Chemical Rocks: Halite• Secondary evidence of presence of evaporites:

– An increase and smooth ROP– Decreased cuttings volume– Eroded or reworked appearance of cuttings– Increased mud salinity– Increased mud viscosity– Decrease and smooth background gas– Salty encrustations on surface of cuttings

• Cuttings – good cubic cleavage, colorless to white (often with a pink to red tinge), soluble, salty taste


Chemical Rocks: Anhydrite and Gypsum

• Determination between anhydrite and gypsum is not always possible at the wellsite, but an attempt should be made


Anhydrite and Gypsum

Gypsum Anhydrite

Formula CaSO4x2H2O CaSO4

Color White, light to dark grey, red, blue, yellow-brown

White, pale grey, red

Structure Selenite crystals, glassy, slightly flexible, fibrous texture

Satin spar, fibrous to lacy, pearly

Massive, fine grained, subvitreous to dull luster

Spongy, white soft

Fibrous, parallel & radiate structures, fine grained

Amorphous, fine grained, massive but cleavable

Luster Pearly, earthy, subvitreous Pearly, glassy, vitreous

Hardness Scratched by a fingernail Scratched by a brass pin

Density 2.3 to 2.37 gm/cc 2.9 to 3.0 gm/cc


Checking For the Presence of Anhydrite and Gypsum

Barium Chloride Test1. Place several cuttings in a bottle and fill with

distilled water2. Agitate and pour off water. Refill and repeat3. Fill bottle half full with distilled water and add 3

drops of HCl and agitate4. Add 2 drops of Barium Chloride5. A pearly white discoloration will confirm the

presence of gypsum or anhydrite


Limestone/Dolomite or Anhydrite/Gypsum?

• To discriminate between limestone / dolomite and anhydrite or gypsum, use HCl, limestone will effervesce, anhydrite and gypsum will not.


Carbonaceous Rocks

• Coal beds are useful marker beds

• Can be inferred from ROP

• Give well defined methane peaks

• Show up quite well in the GR, Density-Neutron logs

• Unusual to encounter coal beds > 6 ft (2 meters) thick

• In geologically young deposits, lignite (brown coal) is found

• There should be signs of vegetal matter in the lignite


Coal: Classification Based On Constituents

• Humic Coal

• Sapropelic Coal


Humic Coal

• Gas-prone source rock• Woody, plant tissue dominant• Divisible by decreasing proportion of volatile

components:– Lignite -> Sub-bituminous -> Bituminous -> Semi-

bituminous

• Laminated, friable in part, jointed, fibrous, bright “jet”-like layers, variable luster, hard/brittle


Sapropelic Coal

• Oil-prone source rock

• Non-woody, comprises of spores, algae and macerated plant material

• Massive unlaminated glassy appearance, conchoidal fracture, firm rather than hard


End of Topic


Oil Show Evaluation


Oil Show Evaluation

• Solid Hydrocarbons and Dead Oil

• Oil show description

• Hydrocarbon Odor

• Oil Staining

• Natural Fluorescence

• Solvent Cut Fluorescence

• Other Tests


Solid Hydrocarbons and Dead Oil

• Solid hydrocarbon refers to hydrocarbons that are in a solid state at surface conditions, usually brittle, and often shiny and glossy in appearance (ex: Gilsonite)

• “Dead oil” is thermally dead solid hydrocarbons that will not fluoresce or give a cut (ex. Anthraxolite)


Gilsonite

• Immature or barely mature oils

• High-quality gasoline, industrial fuel oils and an endless list of other products are produced from gilsonite.


Anthraxolite

• Anthraxolite represent the carbonaceous residue left after hydrocarbons have been overheated and thermally cracked

• Considered to be thermally dead oil


Sample Examination Procedure For HC Shows

1. Take a mud sample, aside from the regular sample or bottoms up sample, when there are significant gas shows. If a significant gas peak arrives in between sampling intervals, a spot sample is caught along with a mud sample.

2. Pour mud sample into a shallow dish and observe under UV light. If nothing is seen, water is added to the mud and the mixture is stirred. Again the sample is observed under UV light.



3. The unwashed sample is also observed under UV light.

4. For the lithological samples, smell the sample first before observing it under the microscope. Observe sample under microscope for staining / bleeding.

5. Place some oil-stained cuttings, if any, into some of the depressions on the spot plate. Observe under microscope.



6. Observe sample tray under UV light. Separate some fluorescing grains and place them in the spot plate.

7. Observe the grains that have been selected in Step 6 under the microscope for stains/bleeding.

8. Use the Solvent Cut Test on the samples in the spot plate. Observe under UV light.

9. Observe cutting samples in plain light.10. Observe the residue.


Observing a Sample Under the UV Box


Order of Oil Show Description

• Free oil in mud: amount, intensity and color• Petroliferous odor: type and strength• Visible oil staining/bleeding: distribution,

intensity and color • Sample Fluorescence: percentage, intensity, color• Solvent cut: speed, character, intensity and color• Cut color and intensity• Cut residue (intensity and color)


Observing Mud Samples

• Mud samples are poured into a container and observed under UV light

• If no droplets of oil is seen, water may be added to reduce the viscosity and the solution is stirred


Rating Oil Shows in Mud Under UV Light

Type Characteristic

1 1mm pops, scattered and few in number; frequently associated with oil found in shale and sandstone containing very slight traces of residual oil

2 2mm pops or larger, few in number, commonly noted in large fractures and residual oil in sandstone; maybe dull and streaky, associated with low gas readings

3 Pinpoints common, along with 2mm or larger pops; frequently observed from sections with fair amounts of oil

4 Common and abundant pinpoint; normally associated with good to fair oil show

5 Abundant pops 2mm and larger, are frequently associated with good shows. In higher gravity oil, the pops surface and spread rapidly


Hydrocarbon Odor

• Always check the sample for petroliferous odor

• Odor may range from heavy, characteristic of low gravity oil, to light and penetrating, for condensate.

• Use general terms for describing hydrocarbon odor: faint, moderate or strong


Oil Staining• The amount of oil staining on cuttings and cores is primarily a

function of the distribution of the porosity and the oil distribution within the pores.

• Check all samples with oil stains under UV light and with a cut solvent

• Check cuttings under UV light that bob to the surface when placed in acid

• The amount, degree and color of the oil stain should be noted• For amount of oil stain the following:

– No visible oil stain, spotty oil stain, streaky oil stain, patchy oil stain, uniform oil stain

• The color of the oil stain is related to the oil’s API gravity


Bleeding Core Sample


Natural Fluorescence• The intensity and color of oil fluorescence is a

useful indicator of oil gravity and mobility• Fluorescence checks should be done ASAP

because fluorescence tends to dull appreciably , due to the loss of volatiles

• The degree of oil fluorescence should be noted as: none, spotty, streaky, patchy, uniform, any combination thereof

• Care must be taken not to confuse mineral and contaminant fluorescence with true formation fluorescence


Fluorescence


Fluorescence: Indication of API Gravity

Gravity (API) Color at 3600A

< 15 Brown

15 - 25 Orange

25 - 35 Yellow to Cream

35 - 45 White

> 45 Blue White to Violet


Mineral Fluorescence

Rock Type Fluorescence Color

Dolomite, Sandy Limestone yellow, yellowish brown

Some Limestones (magnesian) brown

Chalk, chalky limestones purple

Paper Shale yellow to coffee brown, greyish

Fossils yellow-white to yellow-brown

Marl, Clay Marl yellowish to brownish grey

Anhydrite grey brown, greyish, blue


Chemicals Used for Solvent Cut Test

• Chloroform ( we often use on well site now.)• Carbon tetrachloride• Ethylene dichloride• Methylene chloride• 1,1,1 trichloroethane• 1,1,2 trichloroethane• Trichloroethylene• Acetone• Petroleum Ether


Be careful

• Carbon Tetrachloride is a cumulative poison and should not be used

• Proper ventilation is needed when petroleum ether is used• Petroleum ether and acetone must be kept away from open

flame• Do not store chemicals in plastic bottles• Test solvent under UV light before using them• Always work with small quantities in a well-ventilated

area• Remember to wash your hands after using them. Do not

eat without washing your hands after handling them.


Solvent Cut or “Wet Cut” Test

• The speed in which the solvent cut occurs yields useful info

• If the suspected cutting will not initially cut, the test can be repeated. Samples can be dried, crushed or have diluted HCl applied to it

• The residue oil that remains in the spot plate is the oil’s natural color

• Be careful not to get the cutting agent into the rubber of the dropper as it might “contaminate” the solvent by giving it a pale yellowish fluorescence


“Cut”

• A “cut” is the hydrocarbon extracted by the solvent


“Residual Cut”

• The fluorescent ring or residue in the dish after the reagent has evaporated


How To Do A Solvent Cut Test

1. Place a few drops of solvent, enough to immerse the sample, on the sample in the depression in the spot plate or the test tube.

2. Observe the following:1. Cut speed

2. Cut nature

3. Cut color fluorescence and intensity

4. Cut color intensity

5. Residue color and intensity


Solvent Cut Test: Alternate Method

1. Pick out a number of fragments and drop them into a clear one-or- two-ounce bottle or test tube

2. Pour chlorothene or acetone until the bottle is half full

3. It is then stoppered and shaken

4. Observe the color of the solvent


Samples Immersed In Solvent


Cut Speed

• This is an indication of both the solubility of the oil and the permeability of the sample. The speed can vary from instantaneous to very slow.


Cut Nature

• Coloration of the solvent with dissolved oil may occur in a uniform manner, in streaming manner or in a blooming manner. A streaming cut also indicates low oil mobility.


Cut Color Fluorescence and Intensity

• Observe the color and the intensity of the oil in the solvent under both UV and natural lights. The cut color observed under UV light could be called a cut color fluorescence


Cut Color and Intensity

• After observing the sample under UV light observe the sample under natural light. The cut color observed in natural light is just called cut color


Residue Color and Intensity

• Residue color observed in natural light is the true color of the oil


What To Do When A Sample Will Not Cut

• The sample is crushed using the metal probe and it is observed for a solvent cut. The cut is called a crushed cut.

• Sometimes, adding a little dilute acid will produce a solvent cut, called an acid cut.

• Sometimes, you need to let the sample dry before a solvent cut test is performed.


Other Tests for Oil Shows

• Reaction in acid of oil-bearing samples

• “Wettability”

• Acetone-Water test

• Hot Water test

• Iridescence


Reaction In Acid of Oil-bearing Samples

1. Select a cutting or core chip (appx. 1/2 to 2 mm diameter) to be tested. Place the sample in the shallow depression on the spot plate or in a shallow container.

2. Immerse the sample in dilute HCl

3. If oil is present in the rock, surface tension will cause large bubbles to form


Reaction In Acid of Oil-bearing Samples

• The test is very sensitive to the slightest amount of hydrocarbons, even such as found in carbonaceous shale; therefore, it is well to discount the importance of a positive test unless the bobbing effect is clearly evident or lasting iridescent bubbles are observed

• It is very useful as a simple and rapid preliminary check for the presence of hydrocarbons


“Wettability”

1. Let 1 or 2 drops of water fall on the surface of a stained rock fragment

2. If oil is present the water will not soak into the cutting or flow on the surface but will stand on it or roll off as spherical beads

• Not useful in powdered (air drilled) samples


Acetone-Water Test

• The test is done if the presence of oil or condensate is suspected, and provided no carbonaceous or lignitic matter is present in the rock sample


Acetone-Water Test

1. The rock chip or cutting is powdered using a mortar and pestle.

2. Place the powdered rock or cutting in a test tube.

3. Add acetone and shake it vigorously.

4. After shaking it vigorously, filter the mixture into another test tube and an excess of water is added.

5. When hydrocarbons are present, they form a milky white dispersion, in as much as they are insoluble in water, whereas acetone and water are completely miscible.


Hot Water Test

1. Place 500 cc of fresh, unwashed cuttings in a 1000 cc glass beaker or similar container.

2. Pour in hot water with a temperature of at least 170°F (77°C) until it covers the sample to a depth of 1 cm.

3. Observe the oil film that is formed under ultraviolet light and record the amount of oil released using the scale below.


Hot Water Test

Oil Show Amt of surface coveredExtremely weak < 25% covered

Very weak 25-33% covered

Weak 33-50% covered

Fair 50-99% covered

Strong 100% covered


Iridescence

• Iridescence may be associated with oil of any color or gravity, but it is more likely to be observable and significant for the lighter, more nearly colorless oils where oil staining may be absent

• Iridescence without oil coloration or staining may indicate the presence of light oil or condensate


Summary

• Lack of visible stain is not conclusive proof of the absence of hydrocarbons

• Lack of fluorescence is not conclusive proof of the absence of hydrocarbons

• Bona fide hydrocarbon shows will usually give a positive cut fluorescence (wet cut). High gravity hydrocarbons will often give a positive cut fluorescence and/or a residual cut, but will give negative results with all other hydrocarbon detection methods. Minerals which fluoresce will not yield a cut.

• The oil acid reaction test will give positive results when oil is present, but it is very sensitive and may give positive results in the presence of insignificant amounts of hydrocarbons


End of Topic


Handling Cores


Materials Needed to Handle Cores

• Hammer and chisel• Steel measuring tape• Clipboard• Indelible black and red marker pens• Stick• Rags• Pail with water• Plastic core boxes• HUBCO bags• Fibre tape


Materials Needed to Handle Cores

• Hot work permit (optional)• Wax bath (optional)• Wax (optional)• Cling film (optional)• Aluminum foil (optional)• String or wire for dipping (optional)• Core catching trays (optional)• Fire extinguisher (optional)


Preparation Prior To Handling Cores

• Obtain a hot work permit before turning on the wax bath (if waxing is required). Do not overheat the wax. The wax should have a bright appearance. If it has a burnt appearance it will not seal the samples completely.

• Make up plastic core boxes. Core length plus 10% to 15%. Mark the core boxes and then lay them out in order.

• Prepare core catching trays (for conventional cores).


Preparation Prior To Handling Cores

• Get all miscellaneous materials like marker pens, measuring tape, hammer, HUBCO bags, etc. ready


Safety During Core Handling

• Ensure that the core barrel has been checked for H2S

• Never place your hands under the barrel

• Wear safety glasses

• Wear gloves – preferably the hide gloves rather than cotton gloves

• Ensure that forearms are covered


Conventional Core Retrieval

1. The outer core barrel is suspended from the rotary table

2. The inner barrel is removed and then the core catcher is removed

3. Place a mat underneath the core barrel4. Check for the presence of H2S5. The coring hand attaches the core tong handle to

the base of the inner barrel6. The driller raises the inner barrel upon directions

of the coring hand. The core comes out base first.



7. The core catcher is removed and core inside it is placed in the bottom of the first box. Continue filling the core box with core. Note: boxes are 1m or 3 ft long.

8. When 1 meter of unbroken core appears, break it with a hammer. Only when the core is away from the inner barrel should it be handled. If the core breaks into pieces try to rearrange it in the box.

9. Get a core chip sample and place in a HUBCO bag.



10. Mark the core’s top and bottom depth on the core itself.

11. Spread out the cling film and remove the core from the box and put it on top of the cling film. Ensure that it properly orientated.

12. Wrap in foil.13. Tape securely.14. Label the core depths, its top and bottom and its

way up correctly.



15. Wrap wire or string around the sample about 5 cms from each end, to allow dipping in the wax bath.

16. Dip the core into the wax bath. Ensure complete coverage. Minimize the amount of time the sample is immersed in the wax. Ensure that the wax coating is around 4 mm thick all over.

17. Hang the core from a bar to allow the wax to dry. Avoid contact between samples. Do not dip the hot wax in the water.



18. When the core has been completely removed from the barrel, the “rabbit” (a flanged metal cylinder) will appear.

19. Collect any small chips and pieces of core remaining around the barrel. Store it in sample bags.

20. Pack any space in the box to prevent movement of the core.

21. Close the core boxes. Use heavy duty fibre tape to secure the core boxes.



22. Remove the boxes from the area. Ensure that they are properly labeled.

23. Weigh a representative box so that the approximate weight of the shipment is known.


What To Do If Core Is Stuck In Inner Barrel

• Hammering the core barrel

• Pumping using compressed air or mud (preferred)

• Note: Water should not be used.


Safety During Pumping

• Do not stand in front of the of the barrel while pumping is in progress

• Do not peer into the barrel


Sleeved Core Retrieval

1. The core barrel is broken into singles at the surface.

2. The singles are swung onto the pipe deck where the inner core barrel is pulled off the sleeve. Carefully note the relationship of each section of sleeve to the other.

3. Once the sleeve is free, wipe its surface with dry cloth or rags.

4. Draw two lines using marker pens on the sleeve. The black on the left and the red on the right.



5. Locate the top of the core using percussion techniques and a stick.

6. Once located, properly mark the sleeves in intervals of 1 ft or 1 m. Note the total amount of core recovered.

7. Cut the core and sleeve in 3-ft or 0.5/0.25-m intervals.

8. Take core chip samples and place in HUBCO bags.



9. Seal the ends with plastic cups secured by jubilee clips/worm drive clips. The caps can also be additionally sealed by wax (optional).

10. Place the sleeve into the core box.11. Collect any small chips and pieces of core

remaining in the area. Store it in sample bags.12. Pack any space in the box to prevent movement

of the core.13. Close the core boxes. Use heavy duty fibre tape

to secure the core boxes.



14. Remove the boxes from the area. Ensure that they are properly labeled.

15. Weigh a representative box so that the approximate weight of the shipment is known.


Marking Core Sleeves

• Every 1-m or 3-ft interval a long black line is drawn. Short black lines are drawn for every ft or 0.5/0.25 m interval.

• The top and bottom of each 1-m or 3-ft interval is marked by a T or a B, respectively and their corresponding depths.

• Depths are also written for each 1-ft or 0.5/0.25-m interval.

• Arrows showing the way up are drawn on the two lines (red and black).


End of Topic


Side Wall Cores

(SWC)


Warrant for SWC

• ROP

• GAS DATA

• CUTTINGS

• DRILLING FLUID LOGGING DATA

• WIRE LOGGING DATA


SWC Section

• Real Cuttings can not be differ from the false cuttings, and no clear idea about the lithology.

• The section did not have drilling core, as it need core drilling.

• No oil show in cuttings, but there is gas show, being suspected oil-gas layer, which bears oil or gas in the next well.

• Formation having no sure information or having special lithology needing to be verified.


SWC DATA

• SWC section

• Proposal number

• Number of guns

• Number of bullets

• Actual number of core samples

• Core recovery


SWC Data requirement

• Description is same as cuttings.

• SWC affairs should be marked on the materlog.


Masterlog

XX WELL


THE END

wellsite geology

Documents

sample examination procedure

give positive results

positive cut fluorescence

cut color fluorescence

color rock color

solvent cut test

cut color observed

wellsite geology