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2.2 Porosity of reservoir rock (油藏岩石孔隙度) 1 Definition of Porosity 2 Classification of Porosity 3 Factors affecting Porosity 3 Factors affecting Porosity 4 Applications of Porosity 5 Determination of Porosity

2.2 Porosity

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Page 1: 2.2 Porosity

2.2 Porosity of reservoir rock

(油藏岩石孔隙度)

1 Definition of Porosity

2 Classification of Porosity

3 Factors affecting Porosity3 Factors affecting Porosity

4 Applications of Porosity

5 Determination of Porosity

Page 2: 2.2 Porosity

New Words

effective porosity 有效孔隙度

classification 分类

uniform 均匀的

overburden pressure 上覆岩层压力classification 分类

absolute porosity 绝对孔隙度

p 覆岩层压力

pack 充填

cubic packing 立方排列interconnect 连通

factor 因素

rhombohedral packing 菱形排列isolate 隔离

f ti 地层 储层factor 因素 formation 地层、储层

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1 Definition of PorosityThe Constitution of Sandstone

1 Definition of Porosity

Sandstone is formed from

grains that have undergone

sedimentation,compaction

and cementation.

Cementing material poregrain Cementing material poregrain

The Constitution of Sandstone

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1 Definition of Porosity

Porosity(φ) : the ratio of the pore volume in a y(φ) prock to the bulk volume of that rock. express in per cent.in per cent.

Mathematical form is:

pVφ = (1)

bVφ = …….(1)

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Definition of PorosityDefinition of Porosity

EXAMPLE 1

A l d d l i hti 425A clean and dry core sample weighting 425g was 100% saturated with a 1.07 specific gravity brine. p g yThe new weight is 453g. The core sample is 12 cml d 4 i di t C l l t th itlong and 4 cm in diameter. Calculate the porosityof the rock sample.

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Definition of Porosityf f y

SOLUTION

Th b lk l f th l iThe bulk volume of the core sample is:2 3(2) (12) 150.80bV cm= Π =( ) ( )b

The pore volume is:The pore volume is:

31 453 425( ) 26 17V V V cm−= − = =( ) 26.17

1.07p wet dryV V V cmγ

= − = =

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Definition of Porosityf f y

SOLUTION

The Porosity of the core is:

26.17 0.173 17.3%150 80

pVor

Vφ = = =

150.80bV

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2 Classification of Porosity2 Classification of Porosity

(孔隙度分类)

1) Geological classification of porosity

(

1) Geological classification of porosity

Porosity can be classified into two groups:Porosity can be classified into two groups: primary and secondary porosity.

A. Primary porosity 原生孔隙度

B. Secondary porosity 次生孔隙度y p y

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Classification of Porosity

Primary porosity: Primary porosity is that which

f f y

Primary porosity: Primary porosity is that which

was formed at the time of deposition of the sedimentsp

Secondary porosity: secondary porosity was

developed after deposition and burial of the formation.

Sandstone porosity is practically all primary porosity whereas carbonate porosity tends to be secondary p y yporosity.

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Classification of Porosity

2) E i i l ifi ti f2) Engineering classification of porosity (孔隙度的工程分类)p y

From a reservoir engineering standpoint,From a reservoir engineering standpoint,Porosity may be classified as total 、 effective

d d i iand dynamic porosity:

A. Total (absolute) porosity 绝对孔隙度

B Effective porosity 有效孔隙度B. Effective porosity 有效孔隙度

C. Dynamic porosity 流动孔隙度

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The different types of pores are shown in Figure.yp p g

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Classification of Porosityf f y

Figure 1: Effective and ineffective porosity in a cemented siliciclastic sandstone

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Classification of Porosityy

A. Absolute (Total) Porosity

Absolute porosity is the ratio of the total poreAbsolute porosity is the ratio of the total pore volume in a rock to the bulk volume of that

krock, regardless of whether or not those porespaces are interconnected.

tpVφ

b

pa V=φ

Page 14: 2.2 Porosity

Classification of Porosity

B. Effective Porosity

Effective porosity is the ratio of the interconnectedpore volume to the bulk volume.

epVφ

b

epe V=φ

b

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Classification of Porosity

C. Dynamic Porosity

Dynamic porosity is the ratio of the pore

y y

volume that fluid can flow under a certainpressure difference to the bulk volumepressure difference to the bulk volume.

fpVφb

fp

f V=φ

φφφ >> ea f

Page 16: 2.2 Porosity

Classification of Porosity

O l ff ti it h l i ifiOnly effective porosity has real significance

in all reservoir engineering calaulationsin all reservoir engineering calaulations,

because it is only from this type of porosity

that the fluids can move and be recovered.

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Classification of Porosity

● Sandstones have porosities that typically range from 8% to 38%,with an average of 18%. About 95% gof sandstone porosity is effective porosity.

● Carbonates have porosities that typically range f 3% t 15% ith f b t 8% Ab tfrom 3% to 15%, with an average of about 8%. About 90% of carbonate porosity is effective porosity.

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3 Factors Governing Porosity(影响孔隙度的因素)(影响孔隙度的因素)

1) Effect of packing on rock porosity1) Effect of packing on rock porosity

2) Effect of sorting on rock porosity

3) Effect of cementation on Porosity

4) Effect of compaction on Porosity

Page 19: 2.2 Porosity

Factors Governing Porosity

1) Effect of packing on rock porosity

Packing describes the arrangement of the sand(颗粒排列方式的影响)

Packing describes the arrangement of the sand grains relative to one another.

Φ = 47.6% Φ = 25.9%cubical packing rhombohedral packing

Page 20: 2.2 Porosity

Factors Governing Porosity

Page 21: 2.2 Porosity

Factors Governing Porosity

2) Effect of sorting on rock porosity(颗粒分选性的影响)

If the size of grain is notPf If the size of grain is not

uniform ,some small particles are mixed with larger sand ggrains, the porosity will be reduced.

Psi

The more uniform

grain size is ,the

higher porosity is.

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Factors Governing Porosity

3) Effect of cementation on Porosity) y(胶结性质的影响)

The composition of cementing material胶结物成分

The content of cementing material胶结物含量

Cementing type of cementing material胶结类型

Page 23: 2.2 Porosity

Factors Governing Porosity

Table 2.1 Variation of porosity with clay content

Page 24: 2.2 Porosity

Factors Governing Porosity

The higher degree of cementation is,the lower porosity isporosity is.

Page 25: 2.2 Porosity

4) Effect of compaction on PorosityThe compaction increased with depth tends to

squeeze the mineral particles closer.squeeze the mineral particles closer.

Porosity decrease with compaction.

Page 26: 2.2 Porosity

Factors Governing Porosity

4) Effect of compaction on Porosity压实的影响

porosity decrease with depth.

abscissa — porosity

ordinate — depth

The deeper the depth is ,the

hi h th d fhigher the degree of

compaction is.p

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44 Apllications of Porosity(孔隙度的应用)

1) Evaluating formation 评价储集层

(孔隙度的应用)

1) Evaluating formation 评价储集层

Porosity % 25~20 20~15 15~10 10~5 5~0Porosity % 25~20 20~15 15~10 10~5 5~0

Grade Very d good moderate poor

nolgood g p

value

2) Calc lating reser oir oil content 计算原油储量2) Calculating reservoir oil content 计算原油储量

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Apllications of Porosity

Calculating reservoir oil contentg

N=A hΦSN=AShΦSoi

where: As = surface area of the reservoirwhere: As surface area of the reservoir

h = thickness of the formation

Φ= porosityS th t f th lSoi= the percent of the pore volume

occupied by the oil

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5 Determination of Porosityy

(孔隙度的确定)

1) Determination of Porosity by Direct1) Determination of Porosity by Direct Measurements

pV p

bVφ =

b

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Determination of Porosity

Measurment of bulk Volume

A. The method of taking geometrical sizeg g

B. Measurement of bulk volume by displacing mercury

C. Measurement of bulk volume by saturatingy gfluid

D. Measurement of bulk Volume by coating the rock with paraffin 封蜡法p 封蜡

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Determination of Porosity

Measurment of bulk Volume

A The method of taking geometrical sizeA. The method of taking geometrical size

If the sample has a simple geometrical shapIf the sample has a simple geometrical shap

and is not chipped or notched, a sliding caliperand is not chipped or notched, a sliding caliper

is used to measure geometrical size of sample.

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Determination of Porosity

Measurment of bulk Volume

B. Measurement of bulk volume bydisplacing mercury 排汞法

The sample is immersed in the core chamberfilled mercury , The change in mercury level is bulk volumebulk volume.

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A f iApparatus for determing bulk volume

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C fC. Measurement of bulk volume by saturating fluid (饱和流体法)

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i iW W−air immb

W WVρ

=fluidρ

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D. Measurement of bulk Volume by ycoating the rock with paraffin 封蜡法

−−= 1232 wwwwV

ρ−

ρ=

pwfV

ρ — density of paraffinρP — density of paraffin

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Example 2Example 2

A Weight of dry sample in air 20 0 gA. Weight of dry sample in air =20.0 gB.Weight of dry sample coated with paraffin = 20.9 gC. Weight of coated sample immersed in water

= 10.0g 10.0gdensity of paraffin = 0.9g/cc

density of water = 1.00 g/cc

What is bulk volume of the sample ?

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Determination of Porosity

Measurment of Pore VolumeMeasurment of Pore Volume

A. Measurement of pore Volume byA. Measurement of pore Volume by saturating fluid

B. Gas expansion methodB. Gas expansion method

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A. Measurement of pore Volume by p y

saturating fluid

2 1W WV −2 1p

l

=

W1— Weight of dry sample in air

W2 — Weight of saturated sample in air

ρl —density of the liquid, g/ cm3

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Example 4Example 4

A. Weight of dry sample in air =20.0 g

B Weight of sat rated sample in air 22 5 gB. Weight of saturated sample in air = 22.5 g

C Weight of saturated sample in water = 12 6gC. Weight of saturated sample in water = 12.6g

density of water = 1.00 g/ccdensity of water 1.00 g/cc

What is effective porosity of the sample ?What is effective porosity of the sample ?

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B. Gas expansion method

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( ) ( )PV P V V V P V V V V+ + + +( ) ( )2 1 2 1a b f p f pPV P V V V P V V V V+ − + = + − +

1 2a

p fP PV V V V −

= − +1 2p fbP P−

Pa —atmospheric pressure ( absolute ) , MPa;Pb —the vacuum pressure in sample chamber, MPa;P —the pressure after the equilibrium is establishedP —the pressure after the equilibrium is established

in the system, MPa.

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2 3 Compressibility of Porous Rocks2.3 Compressibility of Porous Rocks多孔岩石的压缩性

C ibilit th f ti l h i1.Definition

Compressibility : the fractional change in pore volume of per unit bulk volume with a unitchange in pressure. 1/ MPa

reciprocal megapascal

1 VΔ

reciprocal megapascal

1 Pf

b

VCV P

Δ=

ΔbV PΔ

Page 45: 2.2 Porosity

The depletion of fluids from the pore space of a p p preservoir rock results in a change in the internalstress in the rock, thus causing the rock to bestress in the rock, thus causing the rock to be subjected to a different resultant stress. This change in stress results in changes in the grainchange in stress results in changes in the grain, pore, and bulk volume of the rock.

Pf Pf

Psi Psi

Befor development After development

Page 46: 2.2 Porosity

rock-pore compressibility

Pore compressibility is the fractional change i l f th it lin pore volume of the per unit pore volumewith a unit change in pressure.

1 PP

VCV P

Δ=

ΔPV PΔ

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rock-matrix compressibility

Rock-matrix compressibility is the fractional

change in pore volume of per unit the solid rock

material(grains) volume with a unit change in

1 VΔpressure

1 Ps

s

VCV P

Δ=

Δs

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t t l ibilittotal compressibility

Total compressibility is the fractional change in pore and liqued volume of the per unit bulkin pore and liqued volume of the per unit bulk volume rock with a unit change in pressure.

01 VC Δ V V VΔ = Δ +Δ0t

b

CV P

=Δ 0 P LV V VΔ = Δ +Δ

Ct=Cf + Φ(SoCo+SwCw+SgCg)t f ( o o w w g g)

Page 49: 2.2 Porosity

2.Transform of lab porosity with formation porosityp y p y

实验室内常压下的孔隙度与地层条件下孔隙度转换实 常 度 度转

PC Peφ φ − Δ= 0eφ φ=

PΔ :effective overburden pressure change

PC :rock compressibility

0φ :lab porosity