Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering
Texas A&M UniversityCollege Station, TX 77843-3116
+1.979.845.2292 — [email protected]
Natural Gas Engineering
A Semianalytical p/z Technique for the Analysis
of Abnormally Pressured Gas ReservoirsSPE 71514 | R. Gunawan Gan | M.S. Thesis (2001)
Slide — 1
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
ObjectiveTo present a new technique that can beused to:●Calculate gas-in-place for an abnor-
mally pressured gas reservoir using only average reservoir pressure and cumulative production data.
●Calculate pore volume compressibi-lity as a function of reservoir pressure.
Slide — 2
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Presentation Outline
● Introduction● Overview of Existing Methods● New Method ● Field Examples● Conclusions
Slide — 3
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Introduction●p/z schematic for a normally-pressured
volumetric gas reservoir.
G
p/z
Gp
GG
zp
zp p
i
i 1
Slide — 4
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Introduction●p/z schematic for an abnormally-pressured
gas reservoir.
p/z
Gp G
GG
zppp
zp p
i
ii 1)(1
Gapp
Slide — 5
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Introduction
● Reasons for the non-linear p/z behavior:■ Rock and water compressibility effects —
"rock collapse theory" (Hawkins, 1969).■ Shale water influx (Bourgoyne, 1989).
Slide — 6
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Existing Methods
Methods based on presumed knowledge ofsystem compressibility:
Hammerlindl (Constant Compressibility), 1971
Ramagost (Constant Compressibility), 1981
Yale et al. (Variable Compressibility), 1993
GG
zp
SccSp
zp p
i
i
w
fww 1)1(
)(1
Slide — 7
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Methods based on presumed knowledge ofsystem compressibility (continued):
Fetkovich, Reese, and Whitson - 1991- Derived General Material Balance Eq.- Define cumulative effective compressibility,
wi
ftwftwwie S
pcpcMpcpcSpc
1)]()([)()(
)(
- ce represents the cumulative change in hydrocarbon PV caused by compressi-bility effects (and water influx).
Slide — 8
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Methods which do not require a priorknowledge of system compressibility: Roach - 1981
- very sensitive to initial pressure.- method sometimes doesn’t exhibit
a negative intercept (which is not possible).
Bernard - 1985- using Least Squares approach.- very sensitive to data scatter.
Ambastha - 1991: Type Curve Approach- non-uniqueness problems.
Slide — 9
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
Develops 2 new plotting functions:
1. )/)/(/(versus)( iiie zpzpppc
2. /GGzpzp pii versus)/)/(/(
Requires production data only (p and Gp).
Satisfies both "rock collapse" and "shale water influx" theories.
Slide — 10
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method Uses general material balance equation
(proposed by Fetkovich, et al.).
GG
zpppc
zp p
i
iie 1)(1
Rearranging, we obtain:
GG
zpzpppc pii
ie 1 //1)(
Slide — 11
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method Calculate the ce(pi-p) function for
each p/z versus Gp trend.
ce(pi-p) = ???
ce(pi-p) = ???
Gp
p/z
G GappSlide — 12
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method For early time data (1st straight line):
GG
GG
ppc app
zp
zp
app
zp
zpie
i
i
i
i
)/(1
)/(11)(
For late time data (2nd straight line):
GG
ppc pA
zpzpie
iiA
111)()/(
)/(
where: A is the inflection pointSlide — 13
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
Plot of log ce(pi-p) versus (p/z)/(pi/zi):
(p/z)/(pi/zi)
G/Gapp=0.7
G/Gapp=0.6
G/Gapp=0.8
inflection point
Slide — 14
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Plot of log ce(pi-p) versus (p/z)/(pi/zi) :
(p/z)/(pi/zi)
inflection point
New Method
Slide — 15
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
/GGzpzp pii versus)/)/(/(
Gp/G
(p/z
)/(p i
/zi)
0 1
1
Infl. Point: GpA/G, (p/z)A /( pi /zi )
GG
GG1
/zpp/z p
appii
GG
GGzpzp
/zpp/z p
pAii
A
ii )/1)(/()/(
Slide — 16
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
/GGzpzp pii versus)/)/(/(
Gp/G
(p/z
)/(p i
/zi)
0 1
1
G/Gapp=1
G/Gapp= 0.8
G/Gapp=0.6Inflection point
Slide — 17
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
/GGzpzp pii versus)/)/(/(
Gp/G
(p/z
)/(p i
/zi)
0 1
1
Inflection point
G/Gapp=0.8
Slide — 18
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
/GGzpzp pii versus)/)/(/( Dynamic Type Curve Matching. Automatic Matching using SOLVER
(Excel function for non-linear regression).
Slide — 19
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
Data required for analysis: Fluid property data Initial Reservoir p and T p and Gp data
Slide — 20
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
New Method
Computer program: Visual Basic Application in MS Excel
Easy to use - especially for analysis Only requires MS Excel
Slide — 21
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Data Analysis Sheet
Slide — 22
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 1: G is too low
Slide — 23
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 1: G is too high
Slide — 24
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 1: Correct G
Slide — 25
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 2: Long transition period
Slide — 26
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 3: Early time data
Slide — 27
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 4: Synthetic Dry Gas Case
Slide — 28
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 4: Backcalculated cf
Procedure to calculate cf vs. p from production data:
1. Get )(pce from type curve matching
3. Calculate cf (p):
jfnif pcppcn
jj
1)(
wi
ftwftwwie S
pcpcMpcpcSpc
1)]()([)()(
)(
2. Use the following equation to calculate )(pcf :
Slide — 29
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Example 4: Backcalculated cf
Slide — 30
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Conclusions We have developed a straightforward
approach for analyzing p/z versus Gpbehavior for abnormally pressured gasreservoirs — the approach considersthat two straight-lines must be ob-served on the p/z plot.
The proposed method determinesgas-in-place without using system compressibility data. Only p, Gp, and fluid property data are required.
Slide — 31
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Conclusions (continued)
Our approach of using ce(pi-p) versus(p/z)/(pi /zi) and (p/z)/(pi /zi) versus Gp/Gas dynamic type curve matching func-tions has been shown to work extreme-ly well.
Using our new method, it is possible to calculate rock compressibility as a
func-tion of pressure from p and Gp data
Slide — 32
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
Conclusions (continued)
The "dynamic type curve matching technique" used for calculating gas-in-place from production data is more representative (and more stable) than the non-linear optimization method provided by SOLVER.
Slide — 33
Natural Gas Engineering | 26 May - 30 May 2014 (U. Kavala/GREECE) Tom BLASINGAME | [email protected] | Texas A&M U.
T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering
Texas A&M UniversityCollege Station, TX 77843-3116
+1.979.845.2292 — [email protected]
Natural Gas Engineering
A Semianalytical p/z Technique for the Analysis
of Abnormally Pressured Gas ReservoirsSPE 71514 | R. Gunawan Gan | M.S. Thesis (2001)
(End of Presentation)
Slide — 34
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