2.2 Porosity
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Transcript of 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
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
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
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)
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.
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
= − = =
Definition of Porosityf f y
SOLUTION
The Porosity of the core is:
26.17 0.173 17.3%150 80
pVor
Vφ = = =
150.80bV
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
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.
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
The different types of pores are shown in Figure.yp p g
Classification of Porosityf f y
Figure 1: Effective and ineffective porosity in a cemented siliciclastic sandstone
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
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
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
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.
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.
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
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
Factors Governing 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.
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
Factors Governing Porosity
Table 2.1 Variation of porosity with clay content
Factors Governing Porosity
The higher degree of cementation is,the lower porosity isporosity is.
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.
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
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
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
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
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
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.
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.
A f iApparatus for determing bulk volume
C fC. Measurement of bulk volume by saturating fluid (饱和流体法)
i iW W−air immb
W WVρ
=fluidρ
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
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 ?
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
A. Measurement of pore Volume by p y
saturating fluid
2 1W WV −2 1p
l
Vρ
=
W1— Weight of dry sample in air
W2 — Weight of saturated sample in air
ρl —density of the liquid, g/ cm3
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 ?
B. Gas expansion method
( ) ( )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.
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
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
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
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
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)
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