Transcript Document 7168752

Chapter 2
Petroleum Geology and Reservoirs
(石油地質及儲油層)
1
References
石油地質及儲油層 (Petroleum Geology and Reservoir)
Textbook 1
Fundamentals of Petroleum, Petroleum Extension Service,
The University of Texas at Austin, Austin, Texas,1979.
– chapter 1
Textbook 2
Archer, J. S., and Wall, C.G., Petroleum Engineering—
principles and practice, Graham & Trotman, MD, 1986.
– chapter 2
TextBook 3
Donohue, D.A.T., and Lang K.R., A First Course in
Petroleum Technology, International Human Resources
Development Corporation, Houston,1986
– chapter 4.1; 4.2
2
Petroleum Geology
(石油地質)
Geology (地質)
---研究(1)地球的歷史及構造
(2)記錄在岩石的生物(命)形式
Petroleum Geology(石油地質)
---研究地質以預測石油累積之處所
3
地球的形成及構造

地球的形成 —40～50億年前由宇宙塵
(Cosmic dust)的凝結而成

地球內部大構造 —
Core--- heavy (4,400 miles)
Mantle--- Lighter (1,800 miles)
Crust--- 10~30 miles



4
地球內部大構造
Core-- heavy (4,400 miles)
Mantle-- Lighter (1,800 miles)
Crust--- 10~30 miles
5
在地球上，不管您走到哪裡，你都是在岩石
（Rock）的上面。在加州的某些地方，你是
站有岩石的上面20哩處
20哩是多少?
6MILES = 9.6 KILOMETERS
20MILES = 32 KILOMETERS
喜馬拉雅山大約有6哩高
所以20哩是喜馬拉雅山的3倍高，其間
有很多的岩石。
地球表面的變化 -- Rock cycle
噴出
地球內部
heat
Water vapor and gases
形成
Magma
(岩漿)
Primeval(初期的)
Atmosphere(大氣)
地殼冷卻
Cool
Metamorphic
rocks
Igneous rocks
(火成岩)
地殼收縮變形而皺摺
下雨
erosion
heat
pressure
erosion
Sedimentary erosion
rocks
pressure
cementation
Sediments
(沉積物)
7
沉積岩的分類
碎屑岩
礫岩
砂岩
粉砂岩
頁岩
化學岩
碳酸鹽
蒸發岩
石灰岩
白雲石
石膏
硬石膏
鹽岩
碳酸鉀(鉀化
合物)
Clastic
Conglomerate
Sandsonte
Siltstone
Shale
Chemical
Carbonate
Evaporite
Limestone
Dolomite
Gypsum
Anhydrite
Salt
Potash
有機岩
泥炭
煤
矽藻土
石灰岩
Organic
Peat
Coal
Diatomite
Limestone
其他
角岩
Other
Chert
8
Reservoir Rock (Sedimentary Rock)
Prorsity
Reservoir Rock
Permeability
Sandstones (SiO2)
Carbonates
Limestones (CaCO3)
Dolomites (CaCO3, MgCO3)
9
地球的歷史

寒武紀(Cambrian)【約5.5億年前】開始在海洋裡
有大量的生物(生命)
在寒武紀之前為前寒武紀(Precambrian)

地質年代自寒武紀開始
> 地質代年表(Geologic Time Scale)

泥盆紀(Devonian)時期【約3.3億年前】陸上有大
量植物及動物
10
Geological Time Scale
11
地層年代表
12
13
Petroleum accumulation
(石油累積)
Petroleum reservoir
(石油油藏;油藏;油層)

Petroleum accumulation必須具備
(1)Oil ＆ gas 之來源
(2)具有孔隙(porosity)及滲透率
(permeability)之Reservoir Rock
(3) 要有trap(封閉)以阻擋流體的流動
14
石油的來源
15
石油的來源






－石油來自沈積岩的有機物質
－海洋裡大量的生物不停的，緩慢的掉落到海底。
雖然在掉落的過程中，有部分被吃掉或被氧化掉，
但另部份(動物或植物)掉落海底而埋在沼澤或泥濘之
海底
－海底繼續被Sand(砂)，Clay(黏土)及debris等沈積物埋沒
一直到幾千英呎
－沈積物的壓力開始作用。
細菌由殘餘的有機物質中，用掉氧而分解物質，
使其僅存碳及氫
－在高度的壓力及重量的地層影響之下，
Clays變成Shales → 石油產生
16
砂、淤泥及泥土的顆粒沉到水裡，蓋在死的矽藻類以及其他的動植物之上。
而且，水被夾在這些砂、淤泥及泥土的顆粒之中。
不久，這些顆粒，又被其他的動
植物殘骸覆蓋。這個過程，一再
的重複，最後，泥、砂及水累積
達幾千呎厚。
這些砂、泥在堆積過程中，
底部的砂、泥受到上部砂、
泥而擠壓
在河流、湖及海底的泥、砂、水及動植物殘骸所受的覆蓋壓力逐漸的
變大
當覆蓋深度加大而變深，其溫度也增加。經過幾百萬年之後，在適當的壓力及溫度之下，這些泥砂
顆粒就變硬而成為岩石，類似褐色或灰色的水泥。
當動植物的殘骸腐朽之後，形成石油及天然氣，大部分的石油及天然氣係由相當微小的動植物殘骸
而來的
確實的石油及天然氣之形成原因仍不清楚。但是，溫度、壓力及細菌是很重要的因素。

Petroleum formation requires that
organic source clays become mature
by subjection to pressure and
temperature.
18
石油形成的重要條件



225℉ < temperature < 350℉ 有利條件
temperature < 150℉ 不可能形成石油
temperature > 500℉ 有機物質碳化，
不能形成石油
19
Generation of gas and oil
20
21

In geology and oceanography,
diagenesis is any chemical, physical, or
biological change undergone by a
sediment after its initial deposition and
during and after its lithification, exclusive
of surface alteration (weathering) and
metamorphism.
22



Catagenesis can refer to:
Catagenesis (geology) – The cracking
process in which organic kerogens are
broken down into hydrocarbons;
Catagenesis (biology) – Retrogressive
evolution, as contrasted with anagenesis.
23

Metamorphism can be defined as the
solid state recrystallisation of pre-existing
rocks due to changes in heat and/or
pressure and/or introduction of fluids i.e
without melting. There will be
mineralogical, chemical and
crystallographic changes
24


Prolonged exposure to high temperatures, or shorter
exposure to very high temperatures, may lead
progressively to the generation of hydrocarbon mixtures
characterized as condensates, wet gases and gas.
The average organic content of potential source rocks is
about 1% by weight.
The Kimmeridge clay, the principal source rock for North
Sea oil average about 5% carbon (~7% organic mater)
with local rich streaks greater than 40%.
The hydrogen content of the organic matter should be
greater than 7% by weight for potential as an oil source.
25


It is a rule of thumb that for each
percentage point of organic carbon in
mature source rocks, some 1300~1500
cubic meters of oil per km2-m (or 10~40
barrels of oil per acre-ft; or 56-225 ft3/
43560 ft3) of sediment could be generated.
(1.3~1.5 m3oil: 1,000 m3 rock)
It is not, however, necessarily true that all
the oil generated will be expelled or
trapped in porous rock.
26
石油移棲
經過porous bed
有permeability
石油形成
( in source rock)
Migration
Traps＆Reservoir Rocks
由於Compaction of Source bed and ……….
The
migration process involves two main stages, namely from
the source rock and then through a permeable system.
27
Migration of petroleum
-- from the source rock
28
Migration of petroleum
-- from the source rock
** Capillary effect
** Microfractures
Since the generation of petroleum is accompanied by
volume changes which can lead to high local pressures,
there may well be an initiation of microfractures which
provide an escape route into permeable systems such as
sedimentary rocks or fault planes.
The source rock microfractures are believed to heal as
pressures are dissipated.
29
Migration of petroleum
--through a permeable system
** Fluid potential gradient or gravity effect
In the permeable system the transport occurs
under conditions of a fluid potential gradient
which may take the hydrocarbon to surface or to
some place where it becomes trapped.
It might be assumed that less than 10% of
petroleum generated in source rocks is both
expelled and trapped, as shown in the example
of Fig. 2.5.
30
31
Petroleum traps(石油封閉)

The characteristic forms of petroleum trap
are known as
structural traps(構造封閉) and
stratigraphic traps(地層封閉),
with the great majority of known
accumulation being in the former style.
32
地質構造（Geological Structures）
Erosion － Sedimentation
Uplift － wearing down
Upper crust
Fault
Strata or bed
Unconformity
－disconformity
－Angular unconformity
Upward
move
ment
downward
Folds
Arches (or upfold)
→ anticlines
Traughs (or downfold) → synclines
Normal
Reverse
Important to petroleum accumulation
Thrust
Lateral
33
造山運動之應力
所造成
沉積過程所
造成
Figure 1.13. Basic
hydrocarbon reservoirs are
structural and / or
stratigraphic traps.
Figure 1.12. Two
general kinds of
unconformities are
disconformity (A)
and angular
unconformities (B)
and (C).
34
封閉(traps)
封閉(traps)
Structural
traps
Stratigraphic
traps
Structural traps－an arched upper surface
Stratigraphic traps---up-dip termination of porosity (permeability)
Anticline trap
Fault trap
Dome and plug trap
Unconformity
traps
Lenticular trap
Disconformity
Angular
unconformity
Combination traps
35
Cap rock and fluid distribution


Impermeable rocks provide seal above
and below the permeable reservoir rocks.
At equilibrium conditions, the density
differences between the oil, gas and water
phases can result in boundary regions
between them known as fluid contacts, i.e.
gas-oil and oil-water contacts.
36
Structural trap (構造封閉) -- Anticline
Longitudinal view of a typical
anticline. The oil cannot escape
upward because of the impervious
shale bed above the oil sand;
neither can it travel downward
because of the water that is
associated with an accumulation of
this type.
Anticlines－
Of the many types of structural features present in the upper
layers of the earths crust that can trap oil, the most important is
the anticlines－the type of structure from which the greater part
of the word’s oil has been produced.
Anticlines are upfolds of beds in the earth’s crust, and, when the
proper conditions are present, oil accumulates within the closure
of there folds.
37
Structural trap-- Anticline
Lateral, or end view, of a typical
anticline.
Plan view of a typical
anticline, showing locations
of longitudinal view A-B and
lateral view C-D.
38
Structural traps
Figure 1.7. Schematic cross section
shows deformation of earth’s crust by
bucking of layers into folds
Figure 1.8. Simple kinds of
folds are symmetrical
anticline (A), plunging
asymmetrical anticline (B),
plunging syncline (C), and
dome with deep salt core (D).
Figure 1.9. Simplified diagram of
the Milano, Texas, fault.
39
Structural traps– dome & anticline
Figure 1.15. Oil accumulates
in a dome-shaped structure
(A) and an anticlinal type of
fold structure (B). An
anticline is generally long
and narrow while the dome
is circular in outline.
(Courtesy of American
Petroleum Institute)
40
41
Structural traps -- faults
Figure 1.10. Simple kinds of faults
are normal (A), reverse (B), thrust
(C), and lateral (D).
Figure 1.11. Variations of
normal and reverse faulting are
rotational faults (A) and
upthrust faults (B).
42
Structural traps
Figure 1.14. Common types of structural traps
43
Structural trap – fault & anticline
Figure 1.16. Gas and oil are trapped in a
fault trap-a reservoir resulting from
normal faulting or offsetting of strata. The
block on the right has moved up from the
block on the left, moving impervious
shawl opposite the hydrocarbon-bearing
formation. (Courtesy of American
Petroleum Institute)
Figure 1.17. Shown in map view,
fault traps may be simple (A) or
compound (B).
44
Stratigraphic traps
(地層封閉)
45
造山運動之應力
所造成
沉積過程所
造成
Figure 1.13. Basic
hydrocarbon reservoirs are
structural and / or
stratigraphic traps.
Figure 1.12. Two
general kinds of
unconformities are
disconformity (A)
and angular
unconformities (B)
and (C).
46
Stratigraphic traps
Unconformity
－Disconformity
－Angnlar unconformity Pinctout
Sand lenses
Changes in sedimentation
47
Figure 1.22. Oil is trapped
under an unconformity.
(Courtesy of API)
Figure 1.23. Lenticular traps
confine oil in porous parts of the
rock. (Courtesy of API)
48
Stratigraphic trap
An example of a stratigraphic
trap where the oil zone pinches
out.
A stratigraphic trap where sand
lenses are interspersed in a shale bed.
The shale acts as a permeability
barrier
49
Stratigraphic Traps
A stratigraphic trap where
changes in sedimentation
act as a permeability barrier.
An angular unconformity as an
oil trap. The flat-lying shale bed
above the oil zones acts as a
permeability barrier.
50
Stratigraphic traps

Stratigraphic
traps result when
a depositional
bed changes
from permeable
rock into finegrain
impermeable
rock (Fig. 2.8).
51
52
Combination traps

Many reservoirs exist as the result of a
combination of structural and stratigraphic
features.
In the Viking Graben area of the northern
North Sea, the Brent Sand reservoirs are
characteristically faulted deltaic sands
truncated by the Cretaceous unconformity.
53
54
Reservoirs
Reservoir(儲油層)



We may define a reservoir as an accumulation of
hydrocarbon in porous permeable sedimentary rock.
The accumulation, which will have reached a fluid
pressure equilibrium throughout its pore volume at the
time of discovery, is also sometimes known as a pool.
A hydrocarbon field may comprise several reservoirs at
different stratigraphic horizons or in different pressure
regimes.
55
56
Field
An area consisting of a single reservoir or multiple reservoirs all grouped on,
or related to, the same individual geological structural feature and/or
stratigraphic condition. There may be two or more reservoirs in a field that
are separated vertically by intervening impermeable rock, laterally by local
geologic barriers, or both. The term may be defined differently by individual
regulatory authorities.
57
Reservoir(儲油層)

A subsurface rock formation containing an
individual and separate natural accumulation of
moveable petroleum that is confined by
impermeable rocks/formations and is
characterized by a single-pressure system.
58
Reservoir(儲油層)








具有商業價值的石油(及天然氣)地層--reservoir，
所需具備之條件
(1)合適之地層形貌 (Shape/Configuration- traps)
(2)頂蓋層 (cap rock, rock seal)
(3)儲油層之面積(area)大
(4)儲油層之厚度(thickness)大
(5)儲油層之孔隙率(porosity)大
(6)儲油層之含水飽和度(water saturation)小
(7)儲油層之滲透率(permeability)大
59
原油現地藏量
Original oil in place (OOIP)
OOIP = A * h *  * (1-Sw)* 1/Bo
where
A=儲油層之面積(area)
h=儲油層之厚度(thickness)
=儲油層之孔隙率(porosity)
Sw =儲油層之含水飽和度(water saturation)
Bo = 石油地層體積因子(oil formation
volume factor)
60
原油現地藏量
Original oil in place (OOIP)
OOIP = 7758* A * h *  * (1-Sw)* 1/Bo
where
OOIP = 原油現地藏量, STB
A=儲油層之面積(area), acres
h=儲油層之厚度(thickness), ft
=儲油層之孔隙率(porosity), fraction
Sw =儲油層之含水飽和度(water saturation), fraction
Bo =石油地層體積因子(oil formation volume factor)
, bbl/STB
1 acres = 43560 ft2
1 bbl = 5.61458 ft3
61
資源量及蘊藏量定義

資源量
(Petroleum Resources， 或 Resources， 或 Total Petroleum
in place ， 或 Original oil in place )
在一區域或礦區所存在的石油（含天然氣）之總
量，稱為資源量。

蘊藏量(Petroleum Reserves，或 Reserves )
在一已知區域或礦區中，自某一時間點開始，依
據當時的經濟條件(E)、工程技術(F)、及地質條
件(G)下，在可預見的未來所能採收的石油（含
天然氣）之量稱為蘊藏量，或最終採收量。
62
Resources
The term “resources” as used herein is intended to
encompass all quantities of petroleum (recoverable and
unrecoverable) naturally occurring on or within the
Earth’s crust, discovered and undiscovered, plus those
quantities already produced.
Further, it includes all types of petroleum whether
currently considered “conventional” or “unconventional”
(see Total Petroleum Initially-in-Place). (In basin potential
studies, it may be referred to as Total Resource Base or
Hydrocarbon Endowment.)
63
Total Petroleum Initially-in-Place
Petroleum Initially-in-Place is the total quantity
of petroleum that is estimated to exist originally
in naturally occurring reservoirs.
•
Crude Oil-in-place, Natural Gas-in-place and
Natural Bitumen-in-place are defined in the same
manner (see Resources). (Also referred as Total
Resource Base or Hydrocarbon Endowment.)
•
64
Reserves
Reserves are those quantities of petroleum
anticipated to be commercially recoverable by
application of development projects to known
accumulations from a given date forward under
defined conditions.
Reserves must further satisfy four criteria:
They must be discovered, recoverable, commercial,
and remaining (as of a given date) based on the
development project(s) applied.
65
66
67
Reserves (蘊藏量)
Reserves = OOIP * recovery factor
where OOIP = A * h *  * (1-Sw) * 1/Bo
recovery factor (採收因子)
= f( k, E, P, T …)
k = permeability (滲透率)
68

The setting for hydrocarbon accumulation is a
sedimentary basin that has provided the
essential components for petroleum reservoir
occurrence, namely




(a) a source for hydrocarbons,
(b) the formation and migration of petroleum,
(c) a trapping mechanism, i.e., the existence of traps
in porous sedimentary rock at the time of migration
and in the migration path.
The discovery of oil by exploration well drilling in
some of the world’s sedimentary basin is shown
in Figs. 2.1 and 2.2
69
Exploration Success Rate
Exploration Showing a Good Success Rate
23 March 2006 - A strong reflection of New Zealand's
prospectivity for oil and gas has been shown by the
substantial lift in exploration wells drilled since 2000, and
particularly in the past two years.
A strong reflection of New Zealand's prospectivity for oil and gas has
been shown by the substantial lift in exploration wells drilled since
2000, and particularly in the past two years.
In his keynote presentation to the New Zealand Petroleum
Conference, which had a record attendance of more than 520 of
which many were from overseas, Associate Energy Minister Harry
Duynhoven said a total of 149 wells were drilled in the past six years,
of which 74 were wildcats.
In the past 24 months 69 wells were drilled. The Minister said that of
the total 74 wildcats there were 12 discoveries, indicating a success
rate of about 16%.
70
現今的石油鑽井很安全；
很多國家都有制定法令以
保護地表及地下之自然環
境。
在七個探勘井中會有一口具有生產利潤
的生產井
對於不具生產價值的井，必須用水
泥及泥土將井口封閉起來
71
72
Lower right line (0.1 103 m3 oil / km2 ) / (100 willcat wells/104 km2 )
= 104 m3 oil / willcat well = 6.289*104 bbl3 oil / willcat well
Upper left line
(10 103 m3 oil / km2 ) / (1 willcat well/104 km2 )
= 108 m3 oil / willcat well = 6.289*108 bbl oil / willcat well
73
74
Lower right line
Upper left line
(0.01 106 m3 oil discovered / willcat ) /
(1 106 m3 oil discovered/ successful wildcat )
= 1% successful wildcat / willcat
(0.1 106 m3 oil discovered / willcat ) /
(0.1 106 m3 oil discovered/ successful wildcat )
= 100% successful wildcat / willcat
75
76
Reservoir fluids and pressure
77

From a petroleum engineering perspective
it is convenient to think of sedimentary
basins as accumulations water in areas
show subsidence into which sediments
have been transported.
Reservoir fluids and pressure
Gas
Oil
water
Reservoir fluids
Water ─
connate water
(connate interstitial water)
Free water
~Aquifer
Gas
Bottom water
Edge water
Solution gas
Free gas
79
Fluid pressures in a hydrocarbon zone
80
Pressure gradient equation

In a water column representing vertical pore fluid
continuity, the pressure at any point (Px) is
approximated by the relationship
Px = X．Gw
or Px = X．Gw + C
where X = the depth below a reference datum (such
as sea level)
Gw = the pressure exerted by unit height of
water, or pressure gradient
Gw = f (T, salinity)
Gw = 0.433 psi/ft (or 9.79 kpa/m) for fresh water
Gw = 0.44 psi/ft (10 kpa/m) ~ 0.53 psi/ft (12 kpa/m)
for reservoir water system
81
Hydrocarbon pressure regimes

In hydrocarbon pressure regimes

dP
( ) water  0.45
dD
psi/ft

dP
( ) oil  0.35
dD
psi/ft

dP
( ) gas  0.08
dD
psi/ft
82
Pressure gradient ranges

In reservoir found at depth between 2000 m
SS and 4000 m SS, we might use a gradient of
11 kpa/m to predict pore fluid pressures
around 220 bars to 440 bars.
83
Fluid pressures in a hydrocarbon zone
84
85
Reservoir pressure
Normal pressure
Reservoir pressure
Abnormal pressure
－Artesian effect
86
Abnormal hydrostatic pressure
( No continuity of water to the surface)


dP
P  (
) water  D  14.7  C
dD
[=] psia
Normal hydrostatic pressure
c=0


Abnormal (hydrostatic) pressure
c >> 0 → Overpressure (Abnormal high pressure)
c << 0 → Underpressure (Abnormal low pressure)
87
89
Conditions causing abnormal fluid pressures

Conditions causing abnormal fluid pressures in enclosed
water bearing sands include



Temperature change ΔT = +1℉ → ΔP = +125 psi
in a sealed fresh water system
Geological changes – uplifting; surface erosion
Osmosis between waters having different salinity,
the sealing shale acting as the semi permeable
membrane in this ionic exchange; if the water within
the seal is more saline than the surrounding water
the osmosis will cause the abnormal high pressure
and vice versa.
90
91
92
93
94
Abnormal high pressure


All show similar salinity gradients but different
degrees of overpressure, possibly related to
development in localized basins.
Any hydrocarbon bearing structure of substantial
relief will exhibit abnormally high pressure at the
crest when the pressure at the hydrocarbonwater contact is normal, simply because of the
lower density of the hydrocarbon compared with
water.
95
Causes of abnormal pressure

Abnormal fluid pressures are those not in initial
fluid equilibrium at the discovery depth.
Magara (1978) has described conditions leading
to abnormally high and abnormally low
pressures. Some explanations lie in reservoirs
being found at pressure depths higher or lower
than the depths at which they became filled with
hydrocarbon. This may be the result of upthrust
or downthrown faulting.
96
Causes of abnormal pressure


Overpressure from the burial weight of
glacial ice has also been cited.
In Gulf coast and North Sea reservoirs,
overpressure is most frequently attributed
to rapid deposition of shales from which
bound water cannot escape to hydrostatic
equilibrium. This leads to overpressured
aquifer-hydrocarbon system.
97
2.3 Fluid pressures in a hydrocarbon zone
98
Are the water bearing sands abnormally
pressured ?

If so, what effect does this have on the extent of
any hydrocarbon accumulations?
99
Pressure Kick – Oil and Water
5000
oil
OWC
water
D=5500ft
5200
5500
5600
Pw=2265
Pw=2355
Po=2315
P(psia)
Po=2385
Pw=Po=2490
Pw=2535
Depth(ft)
Pw  0 . 45 * D  15 [  ] psia in water zone
Pw ( at D  5600 ft )  0 . 45 * 5600  15  2535 psia
Pw ( at D  5500 ft or at OWC )  0 . 45 * 5500  15  2490 psia
Po ( at D  5500 ft or at OWC )  2490
 0 . 35 * D  C o
or C o  2490 - 0.35 * 5500  565
 P o  0.35 * D  565 in oil zone
Po ( at D  5200 ft )  0 . 35 * 5200  5 65  2385 psia
Pw ( at D  5200 ft )  0 . 45 * 5200  15  2355 psia
Po ( at D  5000 ft )  0 . 35 * 5000  565  2315 psia
Pw ( at D  5000 ft )  0 . 45 * 5000  15  2265 psia
100
pressure kick-gas and water
Gas
D=5500ft
GWC
5200
Pw=2355
P(psia)
Pg=2450
Pg=2466
5500
5600
water
Pw  0.45 * D  15
5000
Pw=2265
Pw=Pg=2490
Pw=2535
Depth(ft)
in
water
zone
Pw ( at
D  5600 ft )  2535 psia
Pw ( at
D  5500 ft
GWC )  2490 psia
Pg ( at
D  5500 ft
GWC )  2490
 0.08 * D  C g
or
C g  2490  0.08 * 5500  2050
 Pg  0.08 * D  2050
in
gas
Pg ( at
D  5200 ft )  0.08 * 5200  2050  2466 psi
Pw ( at
D  5200 ft )  2355 psia
Pg ( at
D  5000 ft )  0.08 * 5000  2050  2450 psia
Pw ( at
D  5000 ft )  2265 psia
zone
101
pressure kick-gas, oil and water
5000
Gas
oil
D=5500ft
Pw=2355
Pw=2400
Pw=2445
5200
5300
5400
5500
5600
GOC
D=5300ft
OWC
water
Pg=2396
Pw=2265
P(psia)
Pg=2412
Po =Pg=2420
Po=2455
Pw= Po=2490
Pw=2535
Depth(ft)
p w  0.45 * D  15
in
water
zone
p w ( at
D  5600 ft )  2535 psi
p w ( at
D  5500 ft
OWC )  2490 psia
po ( at
D  5500 ft
OWC )  2490 psia
 0.35 * D  Co
or
 po  0.35 * D  565
in
Co  565
oil
zone
po ( at
D  5400 ft )  0.35 * 5400  565  2455 psia
p w ( at
D  5400 ft )  0.45 * 5400  15  2445 psia
po ( at
D  5300 ft
GOC )  0.35 * 5300  565  2420 psia
p w ( at
D  5300 ft
GOC )  0.45 * 5300  15  2400 psia
po ( at
D  5300 ft
GOC )  p g ( at
D  5300 ft
GOC )  2420 psia
 0.08 * D  C g
or
C g  1996
 p g  0.08 * D  1996
p g ( at
D  5200 ft )  0.08 * 5200  1996  2412 psia
p w ( at
D  5200 ft )  2355 psia
p g ( at
D  5000 ft )  0.08 * 5000  1996  2396 psia
p w ( at
D  5000 ft )  2265 psia
102
Pressure Kick
5000x0.45+15
2265Psi
2369Psi
P
5000
5100
5200
5300
5400
5500
GAS
Pg=P0 =2385Psi
GOC (5200ft)
GOC
OIL
OWC
Pg=Pw =2490Psi
OWC (5500ft)
Water
D
5500x0.45+15




Assumes a normal hydrostatic pressure regime Pω= 0.45 × D + 15
In water zone
at 5000 ft Pω(at5000) = 5000 × 0.45 + 15 = 2265 psia
at OWC (5500 ft) Pω(at OWC) = 5500 × 0.45 + 15 = 2490 psia
103
Pressure Kick
5000x0.45+15
2265Psi
2369Psi
P
5000
5100
5200
5300
5400
5500
GAS
Pg=P0 =2385Psi
GOC (5200ft)
GOC
OIL
OWC (5500ft)
OWC
Pg=Pw =2490Psi
Water
D
5500x0.45+15





In oil zone Po = 0.35 x D + C
at D = 5500 ft , Po = 2490 psi
→ C = 2490 – 0.35 × 5500 = 565 psia
→ Po = 0.35 × D + 565
at GOC (5200 ft) Po (at GOC) = 0.35 × 5200 + 565 = 2385 psia
104
Pressure Kick


In gas zone Pg = 0.08 D + 1969 (psia)
at 5000 ft Pg = 0.08 × 5000 + 1969 = 2369 psia
105
Pressure Kick
2450Psia
2265Psia
P
P
5000
5100
5200
5300
5400
5500
GAS
hydrostatic
pressure
GOC
OIL
OWC
P0=Pw =2490Psia
5000
5100
5200
5300
5400
5500






GAS
GWC
Pg=Pw=2490Psia
Water
D

Gas pressure
gradient
Water
D
In gas zone
Pg = 0.08 D + C
At D = 5500 ft, Pg = Pω = 2490 psia
2490 = 0.08 × 5500 + C
C = 2050 psia
→ Pg = 0.08 × D + 2050
At D = 5000 ft
Pg = 2450 psia
106
Overburden pressure

There is a balance in a reservoir system
between the pressure gradients representing
rock overburden (Gr), pore fluids (Gf) and
sediment grain pressure (Gg).
The pore fluids can be considered to take part of
the overburden pressure and relieve that part of
the overburden load on the rock grains.
Gr =Gf + Gg
Overburden gradient
The magnitude of the overburden gradient
is approximately 1 psi/ft (22.6 kpa/m).
For 100% rock (sand) Gg = 0.433 x 2.7 = 1.169 psi/ft
For 100% water
For  =20% rock
Gf = 0.433 psi/ft
Gr = 0.2 x 0.433 +0.8 x 1.169
= 1.022 psi/ft
Fluid Pressure Regimes
The total pressure at any depth
= weight of the formation rock
+ weight of fluids (oil, gas or water)
[=] 1 psi/ft * depth(ft)
Fluid Pressure Regimes

Density of sandstone
gm 2.2lbm (0.3048 100cm)3
 2.7 3 
cm 1000 gm
(1 ft)3
 168.202
lb
1slug

ft 3 32.7lbm
slug
 5.22 3
ft
Pressure gradient for sandstone

Pressure gradient for sandstone
p  gD
p
 g
D
 5.22  32.2  168.084
lbf
ft 3
lbf
1 ft 2
lbf
 168.084 2
 1.16 2
( psi / ft )
2
ft  ft 144in
in  ft
Overburden pressure





Overburden pressure (OP)
= Fluid pressure (FP) + Grain or matrix pressure(GP)
OP=FP + GP
In non-isolated reservoir
PW (wellbore pressure) = FP
In isolated reservoir
PW (wellbore pressure) = FP + GP’
where GP<=GP
In a perfectly normal case , the water pressure at any depth
Normal hydrostatic pressure









In a perfectly normal case , the water pressure at any
depth
Assume :(1) Continuity of water pressure to the surface
(2) Salinity of water does not vary with depth.
P  (
(
dP
) water  D  14.7
dD
dP
) water  0.4335
dD
dP
( ) water  0.4335
dD
[=] psia
psi/ft for pure water
psi/ft
for saline water
GWC error from pressure measurement

Pressure = 2500 psia
at D = 5000 ft
in gas-water reservoir
GWC = ?
Sol.
Pg = 0.08 D + C
C = 2500 – 0.08 × 5000
= 2100 psia
→ Pg = 0.08 D + 2100

Water pressure Pω = 0.45 D + 15











At GWC Pg = Pω
0.08 D + 2100 = 0.45 D + 15
15
D = 5635 ft (GWC)
Pressure = 2450 psia
at D = 5000 ft
in gas-water reservoir
GWC = ?
Sol.
Pg = 0.08 D + C
C = 2450 – 0.08 × 5000
= 2050 psia
→ Pg = 0.08 D + 2050
Water pressure Pω = 0.45 D + 15
At GWC Pg = Pω
0.08 D + 2050 = 0.45 D +
D = 5500 ft (GWC)
Results from Errors in GWC or GOC or OWC

GWC or GOC or OWC location
affecting
volume of hydrocarbon OOIP
affecting
OOIP or OGIP
affecting
development plans
2.4 Reservoir Temperature

Reservoir temperature may be expected to
conform to the regional or local geothermal
gradient.
In many petroliferous basins this is around 0.029
k/m (1.6oF/100 ft).
The overburden and reservoir rock, which have
large thermal capacities, together with large
surface area for heat transfer within the
reservoir, lead to a reasonable assumption that
reservoir condition processes tend to be
isothermal
118
119
Reservoir pressures


Hydrocarbon reservoirs are found over a wide
range of present day depths of burial, the
majority being in the range 500 – 4000 m ss.
In our concept of the petroliferous sedimentary
basin as a region of water into which sediment
has accumulated and hydrocarbons have been
generated and trapped, we may have an
expectation of regional hydrostatic gradient.
120

The primary depositional processes and
the nature of the sediments have a major
influence on the porosity and permeability
of reservoir rocks.
121


Secondary processes, including compaction,
solution, chemical replacement and diagenetic
changes, can act to modify further the pore
structure and geometry.
With compaction, grains of sediment are subject
to increasing contact and pore fluids may be
expelled from the decreasing pore volume. If the
pore fluids cannot be expelled, the pore fluid
pressure may increase.
122
Abnormal pressure

Under certain depositional conditions, or
because of movement of closed reservoir
structures, fluid pressures may depart
substantially from the normal range.
One particular mechanism responsible for
overpressure in some North Sea reservoirs is the
inability to expel water from a system containing
rapidly compacted shales.

Abnormal pressure regimes are evident in Fig.
2.11.
123
Pressure Kick – Oil and Water
124
Pressure kick -- gas and water
125
Pressure kick -- gas, oil and water
126