rock description.pdf

8/10/2019 ROCK DESCRIPTION.pdf

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Notes on Sample Examination & Description1- Sand/Sandstone:

1. Rock Type.Sand SD

Sandstone SST2. Colour/ transparency use colour charts

transparent transptranslucent transl

opaque opqThe grains can also have colours. Eg. Greyish pink translucent.3. Grain Size

1.000-2.000mm Very course v crs0.500-1.000mm Coarse crs0.250-0.500mm Medium med0.250-0.125mm Fine f

Just able to see grains = very fine v f4. SortingVery poorly sorted v ply srtPoorly sorted ply srtModerately sortedWell sorted w srtVery well sorted v w srt

5. RoundnessThis is how sharp the edges of the grains are.

Rounded rndSub rounded sb rndSub angular sb angAngular ang

Rounded Sub Rounded Sub Angular Angular6. Sphericity

Elongate elgSub elongate sb elg

Sub spherical sb sphSpherical sph

7. Cement and matrix.Cement is deposited chemically and matrix mechanically1stput the type of cement/matrix.

Calcareous calc

Dolomitic dolAnhydritic anhyGypsiferous gypSiliceous.silc


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2ndput degree of cementUnconsolidated unconsPoorly cemented p cmtModerately cemented mo cmtWell cemented w cmt

Quartzitic qtzcEg. Predominantly well cemented, occasionally poorly cemented.

8. Hardness/induration.Loose lse

Friable friModerately hard mo hdHardhdVery hard v hd

9. Accessories

Chert chtGlauconite glauc

Lignite lig

Muscovite muscPyrite pyrSulphur sHematite heam

How the accessory mineral is distributed may also be described.Eg. Fine disseminated pyrite of loose pyrite nodules.

10. PorosityThisis the gaps between the grains.

None grains are tight together n v pPoor intergranular porosity pores are not connected p v p

Fair intergranular porosity pores present within grains fr v pGood intergranularporosity Some pores between grains are connectedExcellent intergranularporosity All pores are connected ex v p

11- OIL SHOWS.ALWAYS describe the degree of show whether there is a SHOW or NOT.

Example

SANDSTONE:light grey-brown, friable, medium-coarse grain, rounded,

well sorted, trace calcareous cement, trace glauconitic, faint hydrocarbon odour.

SHOW: faint trace light brown oil stain, fair pale yellow direct fluorescence, strongwhite streaming cut fluorescence, pale yellow UV residue ring, light brown residue

ring.


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2- Limestone/Dolomite:

1. Rock Type.Limestone LSTDolomite DOL

2. Durhams Classification

Mudstone mdstWackestone wkstPackstone pkstGrainstone grst

Boundstone bdstCrystalline carbonate xln CO3

3. Colour of rock use colourcharts.The dominant colour is first. The least significant colour last.

4. Crystal Size1.000-2.000mm very coarse crystalline v crs xln0.500-1.000mm coarse crystalline crs xln0.250-0.500mm medium crystalline m xln0.250-0.125mm Fine crystalline f xlm0.125-0.063mm Very fine crystalline v f xln0.063-0.004mm Microcrystalline micrxln< 0.004mm Cryptocrystalline crypxln

5. Hardness

Brittle britCrumbly cmbSoft sftFriable friFirm frmHard hdVery hard v hd

6. Shape of cuttingsAmorphous amorSub blocky sb blkyBlocky blkyPlaty (flat and thin) pltySplinterysplty

7. Crystal Shape(rarely used)Euhedral (no shape) euhSub Euhedral (Slight shape) sb euhAnhedral (well defined crystal sha pe) anhed

Fiberous (like pieces of material) fib


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8. Sedimentary structures

Fiberous fibSucrosic suc

Vitreous vitGritty gritRough rghSmooth smBituminous bitChalky chkOolitic ool

Styolitic styl

Waxy wxyEarthy rthyGreasy gsy

9. Major Characteristics

Carbonaceous (pieces of coal) carbDolomitic dol

Sandy sdySilty sltyArgilaceous argGlauconitic glauc

Pyritic (fools gold) pyr

Micaceous micac

10. Accessories

Chert chtGlauconite glauc

Lignite (pieces of fossilized wood). lig

Muscovite muscPyrite pyrSulphur s

Haematite heam

11. PorosityNo visible porosity n vp

Poor visible porosity (fracture) p v pFair porosity (Pin point) fr v pGood porosity (Intergranular) gd v pExcellent porosity (Vuggy(Interconnecting)) ex v p


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3- Anhydrite1. Rock Type

Anhydrite ANHY

2. Colour/ transparency use colour chartstransparent transptranslucent transl

opaque opq3. Crystal Size

1.000-2.000mm very coarse crystalline v crs xln0.500-1.000mm coarse crystalline crs xln0.250-0.500mm medium crystalline m xln0.250-0.125mm Fine crystalline f xlm0.125-0.063mm Very fine crystalline v f xln0.063-0.004mm Microcrystalline micrxln< 0.004mm Cryptocrystalline crypxln

4. HardnessBrittle britSoft sftFirm frmHard hdVery hard v hd

Eg. Firm to moderately hard. Can also be more dominant in one hardnesscompared with another. Eg. Predominantly hard, occasionally firm.

5. Shape of cuttings

Amorphous (has no shape) amorSub blocky sb blky

Blocky blky

Platy (flat and thin) pltySplinterysplty

6. Sedimentary structures

Fiberous fibSucrosic suc

Vitreous vit

Gritty gritRough rgh

SmoothsmBituminous bit

7. Major CharacteristicsCalcareous calc

Carbonaceous (pieces of coal) carbSandy sdySilty slty

Argilaceous arg


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4- Claystone/Siltstone:

1. Rock Type.Claystone CLSTSiltstone SLTST

2. Colourof rock use colour charts.

The dominant colour is first. The least significant colour last.3. Hardness

Brittle britPlastic plas

Crumbly cmbSoft sftFirm frmHard hdVery hard v hd

Can grade from one hardness to another. Eg. Firm to moderately hard.Can also be more dominant in one hardness compared with another.Eg. Predominantly hard, occasionally firm.

4. Shape of cuttingsAmorphous (has no shape) amorSub blocky sb blkyBlocky blky

Platy (flat and thin) plty

Splinterysplty

5. Sedimentary structuresWaxy (looks like a candle)wxyEarthy (looks like dirt) rthyLaminated (thin beds through the sample beware of PDC cuttings) lamRough rgh

Greasy gsy

Smooth sm


Carbonaceous (pieces of coal) carbDolomitic dolSandy sdy

Silty (for claystone description only) slty

Argilaceous (for siltstone description only) argGlauconitic glauc

Pyritic (fools gold) pyrMicaceous micac


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7. AccessoriesChert chtGlauconite glauc

Lignite lig

Muscovite musc

Pyrite pyrSulphur sHaematite heam

How the accessory mineral is distributed may also be described.Eg. Fine disseminated pyrite of loose pyrite nodules. Lse pyr nod

8- Gradational changes.If the Claystone is becoming increasingly calcareous:CLAYSTONE CALCAREOUS CLAYSTONE ARGILLACEOUS LIMESTONE.

If the Claystone is becoming siltier:

CLAYSTONE SILTY CLAYSTONE ARGILLACEOUS SILTSTONE.

CLAYSTONE: dark grey, occasionally dark green/grey, firm to hard, slightly fissile,trace calcareous, rare glauconitic, slight earthy texture


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5- Halite

1. Rock TypeHalite HAL

2. Colour/ transparency use colour chartstransparent transp

translucent translopaque opq

3. Crystal Size> 2.000mm Massive crystalline mass xln1.000-2.000mm very coarse crystalline v crs xln0.500-1.000mm coarse crystalline crs xln0.250-0.500mm medium crystalline m xln0.250-0.125mm Fine crystalline f xlm

0.125-0.063mm Very fine crystalline v f xln0.063-0.004mm Microcrystalline micrxln< 0.004mm Cryptocrystalline crypxln

4. HardnessBrittlebritSoft sftFirm frmHard hd

Very hard v hdCan grade from one hardness to another. Eg. Firm to moderately hard. Can alsobe more dominant in one hardness compared with another. Eg. Predominantly

hard, occasionally firm.

5. Shape of cuttingsAmorphous amor

Sub blocky sb blkyBlocky blky



Carbonaceous (pieces of coal) carb

Sandy sdySilty slty

Argilaceous arg


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6- Tuff

1. Rock TypeTuff TF

2. Colour/ transparencyUsecolour charts

3. HardnessBrittlebritSoft sftFirmfrmHardhdVeryhardv hd

Can grade from one hardness to another. Eg. Firm to moderately hard. Can also

be more dominant in one hardness compared with another. Eg. Predominantly


4. Shape of cuttingsAmorphous amorSub blocky sb blkyBlocky blky


5. AccessoriesChert cht

Glauconite glaucLignite lig

Pyrite pyrSulphur s


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7- Coal/Lignite1. Rock type

Coal COAL

Lignite LIG

2. ColourUsecolour charts3. Lustre

Dull dull

Vitreous vitWaxy wxyEarthy rthy

4. FractureAngular angConchoidal conch

Sub conchoidal sb conch

5. HardnessBrittle britSoft sftFirm frmHard hdVery hard v hd

Can grade from one hardness to another. Eg. Firm to moderately hard. Can alsobe more dominant in one hardness compared with another. Eg. Predominantly


6. CompactionPoorly compacted p cptModerately compacted mo cptWell compacted w cpt

7. Major CharacteristicsBituminous bitArgillaceous argPyritic (fools gold) pyr

8. Fossils

Occasionally plant remains


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Oil Show Evaluation1-O D O U R The smell should be described in the range of faint, fair to strong, as this willnormallydistinguish between condensates, light oils and heavy oils.2-C h e c k t h e w e t s a m p le u n d e r m i c ro s c o p e Color[light brown to dark brown]

Distribution[spotty, streaky, patchy or uniform]3-C h e c k t h e s a m p le u n d e r f lu o r o s c o p e ( F l u o r e s c e n c e )Intensity and Brightness[color depth]4-Sam ple Cut w i th so lvent ( leach ing ou t o f hydrocarbons f rom rock)- Normal Cut(for permeable rocks)- Crush Cut(for impermeable rocks)

Nature[diffuse, streaming, blooming]Speed[slow, fast]

Color [pale blue, blue/white to pale white, milky white or pale yellow]5-Na tura l cut (so lvent co lor in na tura l light im m ed iate ly af ter cut )Color[Slight discoloration to dark brown]6-Residue (af ter solvent evaporat ion)

Natural Residue (In natural light)UV Residue (Under fluoroscope)Color[Light to dark brown]EXAMPLE1 :

EXAMPLE2 :

SS: CLR -WH, F-MGN, MOD SRT, SBANG,HD, W/CAIC CMT, HI GLAUC, FRI,

GD POR, W/ 50%STK, LT BRN O STN, STK,BRI YEL FLU, STRG YEL STRMCUT, BRI YEL RING.

Sandstone:Clear to white, fine to medium grained, moderately sorted, subangular, hard, with calcareous cement, highly gluconitic, friable, good porosity,


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with 50%streaky, light brown oil staining, streaky, bright yellow fluorescence,strong yellowstreaming cut, bright yellow ring.

- If there is little or no cut then a crush cut can be performed. This is when a

sample iscrushed slight before adding the solvent. A crush cut will indicate a rockwith lowpermeability.- A crush cut is described as a normal cut but it must be noted that a crush cut

wasperformed.- If performing a cut on chalk, the sample must be DRY before attempting the cut,aswet chalk will always produce a weak cut due to poor permeability and surface

tension-Chemicals Used for Solvent Cut Test

Trichloroethane, Propanol, Acetoneand Chloroform

SUMMARY


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Chemical Tests1-HCl Effervescence

A quick test can be made with 10%hydrochloric acid to distinguish between calcite

and dolomite.

Separatethe cuttings from the sample tray and place in a porcelain spot tray. Adda few drops ofacid to the sample and view the results: -Calcite:Immediate and violent effervescence, completely dissolving the sample.

Dolomite:Delayed and slow effervescence, increasing on heating the sample.Mixture:Intermediate reaction.

2-HCl Oil Reaction

If oil is present, large bubbles will form on a cutting when it is immersed in dilute

HCl.

3-Swelling

Significant swelling or flaking in water is characteristic of montmorillonite or

smectite clays anddistinguishes them from kaolinite and illite clays.On adding distilled water to clay, the swelling can be described as follows:Non swelling -No break upHygroturgid -Random swellingHygroclastic -Swelling into irregular piecesHygrofissile - Swelling into flakes (Flaking)Cryptofissile -Swelling into flakes after adding dilute HCl

Swelling clays will also tend to be soft and sticky (although oil-based and inhibitive

mud systems will prevent swelling) making sample washing and sample description

very difficult.

4-Sulphate test Gypsum and Anhydrite

To determine the presence of gypsumor anhydrite use the following procedure:-Crush 2g of washed, dried sample and place in a test tube.-Add 5ml of dilute 10%HCl acid.-Heat-Filter off residue and place in a clean test tube.

-Add approximately 10drops of Barium Chloride (BaCl2)If a white precipitate forms, then the sample is indeed a Sulphate eithergypsum or anhydrite.

To distinguish between the two, it should be noted that gypsum is not so common

in the subsurface, therefore, the sample will typically be anhydrite. Also anhydriteis commonlyassociated with dolomite.

However, to confirm the distinction use the following procedure:-Heat the same residue until evaporations begins-Leave for 15mins

If the sample is gypsum, fine fibrous crystalswill form.


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5-Chloride Test

To confirm the presence of salt or Halite (NaCl) the following test can be used: -Crush 2g of washed, dried sample and place in a test tube.-Heat in distilled water and filter off the residue-Place the residue in a clean test tube-Add 10drops of Silver Nitrate (AgNO3)If a white precipitateforms then chlorides are present.

6-Alizarin Red

This is another test to distinguish between calcite and dolomite.

This can simply be dropped on to the cuttings if calcite is present it will turn a

deep red Colour while everything else remains uncolored.

7-Cement Test

After drilling through casing shoes at the start of a new hole section, it is useful to

confirm thepresence of cement.As it is alkaline, this can be done by adding phenolphthalein (pH indicator) af terwashing thesample. I f the cuttings turn bright purplethen they are cement.


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SAND STONE CLASSIFICATION1- MINERALOGICAL COMPOSTIONSand stone mineralogically consist of the following:-

1-Quartz (SiO2) silica 2-Feldspars 3-Rock fragment 4-Clay minerals

5-Heavy mineralsThere are three factors play very important rule in the distribution, spreading and

presence of these minerals in any sand stone sample1-Availability: it means how much the mineral present in the pre-exiting rock(quantity)2- Stability: it refers to the chemical stability of the mineral (its resistance toattack by chemical solutions)3- Durability: it refers to the physical or mechanical stability of the rock.2- SAND STONE MATURITY

It means how much the sand stone sample is matured:1- Mineralogical maturity: -it depend on the amount of the minerals which had

high stability and durability in the sample where as this ratio increase the maturityincrease2- Textural maturity:Most of rocks consist of a- framework b-matrix c-cement-so textural maturitydepends on:1- The ratio between the framework and matrix(If matrix ratio less than 15%the rock be texturally mature-If matrix ratio morethan 15%the rock be texturally immature)2- Sorting(If rock is well sorted it called texturally mature rock If rock is poorly

sorted it called texturally immature rock)3- Roundency(If rock grains are well rounded it called texturally mature rock Ifrock grains are angular it called texturally immature rock)

3-SAND STONE CLASSIFICATIONDepending on the ratio between framework and matrix in the sample sand stonecan be classified into:1- Arenite group: in which the matrix ratio be less than 15%.( high energymedia of deposition and coarse grains sample)2-Wacky group: in which the matrix ratio be more than 15%.( low energy media

of deposition and fine grains sample with high clay content)

4- SAND STONE DIAGENESIS1-Compaction processlead to decrease in porosity and permeability

2-Cementationbythe chemically precipitated matter (calcareous, siliceous,Ferreganous, kaolinitic). Depend on the ph of the medium.


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LIMESTONE CLASSIFICATIONDurham s Classification

It is textural classification, depending on the ratio between framework (allochems)

and matrix (Micrite) in the sample.

1. MudstoneComposed of lime mud (smaller than 20microns) and less than10%grainsMud supported.2. Wackestone

Composed primarily of lime mud, with more than 10%grains( larger than 20microns) Mud supported.3. Packstone

Composed primarily of grains, and grain supported. Greater than10%interstitialmud matrix and occasionally sparry calcite orpore space.4. Grainstone

Composed of grains, and grain supported. Less than 10%interstitial mud matrix.5. Boundstone

Original constituents were bound together and supported inplace, by organic

growth.6. Crystalline

All original textures are lacking due to the effects ofrecrystallization. Distinctcrystal faces, with occasional relicts.LIME STONE DIGENESIS

1-Dolomitization process by replacement of Ca with Mg ions which lead to increasethe secondary porosity2-Dissolution by the action of acidic solution or change in PH of the medium

Flow chart to determine the limestone type


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BASIC TERMS

1-Sphericity:Refers to a comparison of the surface area of a sphere of the samevolume asthe grain,with the surface area of the grain itself.

2-Roundness: Roundness, which refers to the sharpness of the edges andcorners of a fragment, is an important characteristic that deserves careful attention

in detailed logging.3-Sorting: Sorting is a measure of dispertion of the size frequency distribution ofgrains in a sediment or rock. It involves shape, roundness, specific gravity andmineralcomposition as well as size.

4-Cement: Is a chemical precipitate deposited around the grains and in theinterstices of sediment as aggregates of crystals or as growths on grains of thesame composition.

5-Matrix: Consists of small individual grains that fill intersections between thelargergrains.(Cement is deposited chemically and matrix mechanically).

6-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

7-Hardness and Indurations

1-H a r d n e s s is a physical parameter based on the amount of force required to break

apart the cutting using a simple probe

2-Indu ra t i ons is the process by which a sediment is converted into a sedimentary

rock. It is function of the type and quantity of the cementSample Hardness

DefinitionHardness

Grains fall apart in dry conditionsLoose

Grains can be detached by fingernails, or a rocksample crumbles between the fingers

Friable

Grains can be detached using a knife or needle.Small chips are easily broken by hand

Moderately hard

Grains cannot be detached using knife of needle.Rock sample fractures between grains

Hard

Rock fractures through grainsVery hard

as in swelling claysSoft

plastic clay, deforms easilyPlastic

as in coalBrittle


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Hardness is a reflection of degree of cementation.1-Soft or friable2-Moderately hard; fairly cemented.

3-Hard; moderately cemented.4-Very hard; well cemented.

8-Micrite & Sparite

1-Micrite: abbreviation of microcrystalline ooze ; a precipitate formed within the

basin of deformation and showing no or little evidence of transport; consists ofcrystals 1-4 m diameter occuring as matrix (dull and opaque ultra fine-grainedmaterialthat forms the bulk of limestones and the matrix of chalk)

2-Spar i te : cement consists of clean calcite crystals, generally longer than micrite,

forming pore filling cement between grains and within cavities

9-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 theform of irregular voids.- Moldic due to the leaching of soluble grains- Fracture10-Crystal Structure Terminology- Anhedral -no visible crystal form- Subhedral -partly developed crystal form- Euhedral -well developed crystal form

11-MOH S SCALE OF MI NERAL HARDNESS

1-TALC 2- GYPSUM 3- CALCITE 4- FLUORITE5- APATITE 6-FELDSPAR 7-QUARTZ 8- TOPAZ9- CORUNDUM 10-DIAMOND

12-CLEAVAGE is the property of a mineral that allows it to break repeatedly alongsmooth, flat surfaces.

13-FRACTURE is defined as the way a mineral breaks other than cleavage.

14-STREAKis defined as the colour of the mineral in powder form

Percentage of Accessory Minerals


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