Reservoir Characterization 1
Reservoir Characterization (Part I) Reservoir stratification (reservoir lithology) Reservoir geometry Porosity, permeability, and water saturation Adjoining j g aquifer q Reservoir fluid properties
Reseroir Characterization 2
Reservoir stratification Most reservoirs are layered because of variations that existed in the depositional environment.
Reseroir Characterization 3
Reservoir Geometry (Areally)
Reseroir Characterization 4
Reservoir Geometry (Vertically)
Reseroir Characterization 5
Porosity Vb − Vma Porosity = φ = = Vb Vb Vp
Reseroir Characterization 6
Rock Matrix and Pore Space
Rock matrix
Pore space
Reseroir Characterization 7
Pore-Space Classification P S Cl ifi ti z Total porosity, φt =
Total Pore Space Bulk Volume z Effective p porosity, y, φe =
Interconnected Pore Space Bulk Volume
Reseroir Characterization 8
Permeability z Permeability is a property of the porous
medium and is a measure of the capacity of the medium to transmit fluids
Reseroir Characterization 9
Absolute Permeability z When the medium is completely
saturated with one fluid, fluid then the permeability measurement is often referred to as specific or absolute
permeability
Reseroir Characterization 10
Effective Permeability z When the rock pore spaces contain
more than one fluid, then the permeability to a particular fluid is called the effective permeability
z Effective permeability is a measure of
the fluid conductance capacity of a porous medium to a particular fluid when the medium is saturated with more than one fluid
Reseroir Characterization 11
Relative Permeability z Relative p permeability y is defined as the
ratio of the effective permeability to a fluid at a g given saturation to the effective permeability to that fluid at 100% saturation
Reseroir Characterization 12
Calculating Relative Permeabilities
z Oil
z Water
z Gas
k ro
k eo = k
k rw
k ew = k
k rg =
k eg k
Reseroir Characterization 13
In-Situ Saturation
Rock matrix
Water
Oil and/or gas
Reseroir Characterization 14
Fluid Saturation z The saturation of the fluid is the fraction of
the pore volume occupied by that fluid
Volume of fluid S= Pore volume
Reseroir Characterization 15
Fluid Saturations z Basic concepts of hydrocarbon
accumulation
– Initially, pore space filled 100% with water – Hydrocarbons y migrate g up p dip p into traps p – Hydrocarbons distributed by capillary forces and gravity – Connate water saturation remains in hydrocarbon zone
Reseroir Characterization 16
Determining Fluid Saturations z Core analysis z Capillary p y pressure p measurements z Electric openhole logs
Reseroir Characterization 17
Adjoining Aquifer The aquifer is the total volume of porous water-bearing g rock in pressure communication with a hydrocarbon reservoir. Areal View
Vertical view
Gas reservoir Gas reservoir
Aquifer water encroaches h ffrom the h side
B tt Bottom water t
Reseroir Characterization 18
Reservoir Fluid Properties The fluid properties of interest to the Reservoir Engineer are th those th thatt affect ff t th the mobility bilit off fl fluids id within ithi the th reservoirs i these are used in material balance calculations Properties at surface conditions for transportation and sales (API, viscosity, oil quality)
Reseroir Characterization 19
Reservoir Fluid Properties Oil Properties – Bubble Point Pressure – Bo – Rs – Bt – Co and μo Gas properties –z – Bg and μg Compositions oil & gas – Properties of the composition/mixture
Reseroir Characterization 20
Real Gas in Reservoir Equation of State:
pV = nZRT
Quantity Description
Unit/Value
p
Pressure
psia
V
Volume
ft^3 ft 3
n
Mole number
lb-moles
Z
Gas compressibility G ibilit factor
di dimensionless i l
T
Temperature
Rankine
R
Universal Gas constant
10.73
Reseroir Characterization 21
Calculating Z (1) 1,1
0
1
2
3
4
5
6
7
8
1,1
NHIEÄT ÑOÄ GIAÛ GIAÛM
3,0 2,8 2,6 2,4 2,2 2,0 1,9 1,8
1,0
0,9
1,0 1,5
1,6 0,8
1,3 11 1,1
1,4
1,7
1,05
1,5
1,1
0,9
1,7
1,45 1,4
07 0,7
1,2
1,35
HEÄ SOÁ LEÄ CH KH Í, Z
0,6
1,4
1,25
1,5
1,5 1,6 1,7 , 1,8 14 1,4 1,9 2,0 2,2
1,2 05 0,5 1,15 0,4
16 1,6
1,3
1,3
2,4 2,6 3,0
1,1
0,3
1,3
1,2 1,05 3,0
1,1
2,8
1,0 1,8 17 1,7 1,6 0,9
1,1
2,6 2,4 2,2 2,0 1,9
7
1,2 1,1 ,
1,0
1,05
1,4 1,3 8
9
10
11
AÙP SUAÁT GIAÛ GIAÛM
12
13
14
Step 1: Calculate pseudo-critical pressure and temperature (Sutton)
0,9 15
ppc = 756.8 −131.0γ g − 3.6γ g2 Tpc = 169.2 − 349.5γ g − 74.0γ g2 Step 2: Calculate pseudo-reduced pressure and temperature:
p
pr
=
p p
pc
;T
pr
T = T pc
Step 3: Use Standings-Katz plot to determine Z
Reseroir Characterization 22
Exercise 1 Calculate z-factor according to the given data as follows
Quantity
Value
Unit
Specific gravity g y
0.665
Dimensionless
Reservoir temperature
213
°F
Reservoir pressure
3250
psia
Reseroir Characterization 23
Solution to Exercise 1 1,1
0
1
2
3
4
5
6
7
8
1,1
NHIEÄT ÑOÄ GIAÛ GIAÛM
3,0 2,8 2,6 2,4 2,2 2,0 1,9 1,8
1,0
0,9
1,0 1,5
1,6 0,8
1,3 11 1,1
1,4
1,7
1,05
1,5
1,1
0,9
p pc = 756.8 − 131.0(.665) − 3.6(.665) 2 = 668 1,7
1,45 1,4
07 0,7
1,2
1,35
0,6
1,4
1,25
1,5
1,5 1,6 1,7 , 1,8 14 1,4 1,9 2,0 2,2
1,2 05 0,5 1,15 0,4
16 1,6
Tpc = 169.2 − 349.5(.665) − 74.0(.665)2 = 369
1,3
1,3 HEÄ SOÁ LEÄ CH KH Í, Z
Step 1: Calculate pseudo-critical pressure and temperature (Sutton)
2,4 2,6 3,0
1,1
0,3
Step 2: Calculate pseudo-reduced pressure and temperature:
1,3
p
pr
= 4 . 87 ; T
pr
= 1 . 82
1,2 1,05 3,0
1,1
2,8
1,0 1,8 17 1,7 1,6 0,9
1,1
2,6 2,4 2,2 2,0 1,9
7
1,2 1,1 ,
Step 3: Use Standings-Katz plot to determine Z
1,0
1,05
1,4 1,3 8
9
10
11
AÙP SUAÁT GIAÛ GIAÛM
12
13
14
0,9 15
Z=0.918
Reseroir Characterization 24
Calculate Z using Dranchuk and Abou-Kassem Correlation F Z = R1 ρ r −
R2
ρr
+ R 3 ρ r2 − R 4 ρ r5 + R 5 (1 + A 11 ρ r2 ) exp( − A 11 ρ r2 ) + 1 = 0
ρ r = 0 . 27 p pr /( ZT
pr
)
R 1 = A 1 + A 2 / T pr + A 3 / T pr3 + A 4 / T pr4 + A 5 / T pr5 R 2 = 0 . 27 p
pr
/ T pr
R 3 = A 6 + A 7 / T pr + A 8 / T pr2 R 4 = A 9 ( A 7 / T pr + A 8 / T pr2 ) R 5 = A 10 / T pr3
A1 = 0 . 3265 ; A2 = − 1 . 0700 ; A3 = − 0 . 5339 A4 = 0 . 01569 ; A5 = − 0 . 05165 ; A6 = 0 . 5475 A7 = − 0 . 7361 ; A8 = 0 . 1844 ; A9 = 0 . 1056 A10 = 0 . 6134 ; A11 = 0 . 7210
Reseroir Characterization 25
Exercise 2: PVT Analysis
Using the data in the table below and assuming real gas behavior, calculate the density of the gas phase under initial reservoir conditions. Compare the results with that of ideal gas behavior.
Component
C1 C2 C3 iC4 nC4 iC5 nC5 C6 C7 C8 C9 C10 H2S CO2 N2 H He Air O2
Mole Percent
Molecular Weight
(1)
(2) 0.85 0 04 0.04 0.03 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0 00 0.00 0.00 0.00 0.02 0.01 0 00 0.00 0.00 0.00
16.043 30 070 30.070 44.097 58.123 58.123 72.150 72.150 86.177 100.204 114.231 128 258 128.258 142.285 34.080 44.010 28.013 4 003 4.003 28.960 31.999
Critical Press. (psia) (3)
Critical Temp. (R) (4) 666.4 706 5 706.5 616.0 527.9 550.6 490.4 488.6 436.9 396.8 360.7 331 8 331.8 305.2 1300.0 1071.0 493.1 33 0 33.0 546.9 731.4
343.00 549 59 549.59 665.73 734.13 765.29 828.77 845.47 913.27 972.37 1023.89 1070 35 1070.35 1111.67 672.12 547.58 227.16 9 36 9.36 238.36 278.24
