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Dan Kami telah memberikan kepada mereka di antara tanda-tanda kekuasaan

(Kami) sesuatu yang di dalamnya terdapat nikmat yang nyata

BATUAN DAN PROPERTI RESERVOIR


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Sedimentary rocks are

groups. These groups

are clastic, chemical

precipitate andbiochemical (or

ogen c .


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Siliciclastic rocks are clastic

noncarbonate sedimentary rocks

that are almost exclusively silica-

bearing, either as forms of

All siliciclastic rocks are formed

by inorganic processes, or

deposited through somemechanical process, such as

stream de osits that are

subsequently lithified. They are

sandstone based rocksaccoun ng or a ou - o

the world oil and gas

ex loration.


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Clastic sedimentary rocks may be regarded

,shale being the finest with particles less

than 0.002 mm, siltstone being a little

bigger with particles between 0.002 to

0.063 mm, and sandstone being coarser. ,

conglomerates and breccias being more

coarse with grains 2 to 263 mm. Breccia

has sharper particles, while conglomerateis categorized by its rounded particles.

Particles bi er than 263 mm are termed

blocks (angular) or boulders (rounded).

Lutite,Arenite

andRudite

are generalerms or se men ary roc w c ay s -,

sand- or conglomerate/breccia-sized

articles.


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The colour of a sedimentary rock is

often mostly determined by iron, an

element which has two major oxides:

iron(II) oxide and iron(III) oxide.

anoxic circumstances and gives the

rock a grey or greenish colour.

ron ox e s o ten n t e orm othe mineral hematite and gives the

rock a reddish to brownish colour. In

arid continental climates rocks are in

direct contact with the atmosphere,an ox a on s an mpor an

process, giving the rock a red or

orange colour


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The size, form and orientationof clasts or minerals in a rock

.

texture is a small-scale

property of a rock, butdetermined many of its large-

scale properties, such as the

permeabililty.Clastic rocks have a 'clastic

ex ure , w c means ey

consist of clasts. The 3D

orientation of these clasts iscalled the fabric of the rock.

Between the clasts the rock

can e compose o a ma r x

or a cement


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e orm o a c ast can edescribed by using four

arameters:

'surface texture' describes the

amount of small-scale relief ofe sur ace o a gra n w c s

too small to have influence on

the general shape;

'rounding' describes the generalsmoothness of the shape of a

'sphericity' describes the degree

in with the grain approaches asphere; and

'grain form' is used to describe

.


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The mineralogy of a clastic rock is

determined b the su lied material

from the source area, the manner of

transport to the place of depositionan t e sta ty o a part cu ar

mineral. The stability of the major

rock formin minerals their

resistance to weathering) isexpressed by Bowen's reaction

. ,

stable, followed by feldspar, micas

and other less stable minerals thatwill only be present when little

weathering occurred.


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The term diagenesis isused to describe all the

chemical, physical, and

biological changes, ,

undergone by a sediment

after its initial de osition

exclusive of surfaceweathering. Some of these

processes cause the

sediment to consolidate: a

,

forms out of loose

material.


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proportion of all

sedimentar rocks.

Carbonate rocks

dominantly consist ofcarbonate minerals like

calcite, aragonite or

.

clasts (including fossils and

ooids of a carbonate rock

can consist of carbonate

minerals. Carbonatesusually have an irregular

structure.


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The most common are

calcite or calcium

carbonate, CaCO3, the

chief constituent ofmes one as we as e

main component of

skeletons); dolomite, acalcium-magnesium

carbonate CaMg(CO3)2;

and siderite, or iron (II)

car ona e, e 3, an

important iron ore.


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,especially in acid, and therefore

forms man erosional landforms.

These include limestone

pavements, pot holes, cenotes,caves and gorges. Such erosion

landscapes are known as karsts.

most igneous rocks, but more

resistant than most other

sedimentary rocks. Limestone is

therefore usually associated withhills and downland and occurs in

regions with other sedimentary

,


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S ecial carbonate t es

Chalk is a special form

of limestone and isformed from the

skeletons of small

crea ures coco s .

Evaporites such as Salt

(CaSO4) can also form

in these environments

.


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Com onents de osited as discrete

grains or crystalsContain lime mud, < 10% grains:

(Lime) Mudstone

Contain lime mud, (matrix

supported) >10% grains:

WackestoneContains lime mud, grain

supported: Packstone

No lime mud, grain supported:

Grainstone

original components bound

together during deposition by

ramewor u ng organ sms,

encrustation or sediment

trapping mechanisms :

Depositional texture not

recognizable. Crystalline


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Vuggy porosity is pore space that

is within grains or crystals or that

is significantly larger than grains

or crystals; that is, pore space that

is not interparticle. This definitiondeviates from the restrictive

definition of vugs used by

Cho uette and Pra 1970 as

nondescript, nonfabric-selectivepores, but it is consistent with the

widespread and less restrictive use

in the oil industry of the term

" "

visible pore space in carbonate

rocks


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Rocks are described

b three ro erties:

Porosity - quantity of

pore space

Permeability- abilityof a formation to

Matrix -major

constituent of therock


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Porosit is a measure of the

void spaces in a material,

and is a fraction of the

total volume, between 01, or

as a percentage between 0

It is defined by the ratio:where VV is the v of void-

space (such as fluids) and VTis the total or bulk volume of

material, including the solidand void components


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Porosity Sandstones

The porosity of a sandstone depends on the

packing arrangement of its grains.The system can

be examined using spheres

In a Rhombohedral packing, the pore spaceaccounts for 26% of the total volume.

With a Cubic packing arrangement, the pore space

.

In practice, the theoretical value is rarely reachedbecause:

a) the grains are not perfectly round, and

b) the grains are not of uniform size.


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Well sorted (grains of

materials have higher porosity

than similarly sized poorlysor e ma er a s w ere sma er

particles fill the gaps between

larger particles). The graphic

illustrates how some smaller

grains can effectively fill the

pores (where all water flow takes

place), drastically reducing

porosity and hydraulic

small fraction of the total volume

of the material.


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Porosit and Grain Size

A rock can be made

up of small grainsor large grains but

have the same

poros y.

Porosity depends

,

not the grain size.


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Primary porosity

The main or original porosity

system in a rock or unconfined

alluvial deposit.

Secondary porosityA subsequent or separate porosity

,

overall porosity of a rock. This can

be a result of chemical leeching of

fracture system. This can replace

the primary porosity or coexist


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Macro porosity :Refers to pores

greater than 50 nm in diameter. Flow

through macropores is described by

bulk diffusion.

Meso porosity :Refers to pores greater

than 2 nm and less than 50 nm in

.

described by Knudsen diffusion.

cro poros y : e ers o pores sma er

than 2 nm in diameter. Movement in

micropores is by activated diffusion.


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DIAGENESIS

subsequent alterations of the rock

such as:Chemical changes,Diagenesis is the

chemical alteration of a rock after

ur a . n examp e s e

replacement of some of the calcium

form dolomite

Mechanical changes - fracturing in atectonically-active region.


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Carbonate porosity is very heterogeneous. It is classified

"primary porosity".

Interparticle porosity:Each grain is

separated, giving a similar porespace arrangement as sandstone.

Intergranular porosity:Pore space

grains which are interconnected.

Intercr stalline orosit :Produced

by spaces between carbonate

crystals.

Mouldic porosity:Pores created by

the dissolution of shells, etc.


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Porosity created after deposition is called

secon ary poros y .

Fracture porosity:

Pore spacing created by thecrac ng o e roc a r c.

anne poros ty:

Similar to fracture porosity but larger.

Vuggy porosity:

fragments, but unconnected.


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Permeabilit Definition

through a formation depends

on:e pressure rop, e

viscosity of the fluid and The

permeability.

The pressure drop is a

reservoir property.

The viscosity is a fluid

property.

The ermeabilit is a measureof the ease at which a fluid

can flow through a formation


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Permeability and Rocks

Relationships exist between permeability

they are not universal.

A rock must have porosity to have any

.

The unit of measurement is the Darcy.

Reservoir permeability is usually quoted in

m arc es m .

In formations with large grains, the

permeability is high and the flow

rate lar er.In a rock with small grains the

permeability is less and the flow


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Reservoir rocks need

successful:

Pore spaces able to

retain hydrocarbon.Permeability which

a ows e u o

move.


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