D ecline C urve urve A nalysi nalysiss for Estimating EU R ’s (and O O IP’s) IP’s ) Carolyn Coolidge
Decline Curve Analysis • Three basic decline curve equations • All of the equations equations give you the ability ability to predict cumulative production or production rate at some point in time.
We are not concerned with time • To estimate OOIP we need to know the E stimated U ltimate R ecovery (EUR) and the Recovery Factor – We can get EUR directly from a graph – We use a standardized average recovery factor of 35% for all reservoirs undergoing secondary recovery. (Not applied to Tertiary Recovery)
Tensleep Fm., Beaver Creek , WRB 3500000
3000000
Y=ax + b
n 2500000 o i t c u d 2000000 o r P e v i t 1500000 a l u m u C 1000000
y = -3,121x + 3,359,858
500000
0 0
500
1000
1500
Rate BPD
2000
2500
VOILA • Y = a x + b • b = EUR • EUR / recovery factor = OOIP
Complications • Lack WOGC C reservoir production
data prior to 1978 • Engineering changes after a pseudosteady state decline • Secondary vs. Tertiary recovery • Poor (or nonexistent ) decline • Terminology
Tensleep Fm., Beaver Creek , WRB 3500000
3000000
Y=ax + b n 2500000 o i t c u d 2000000 o r P e v i t 1500000 a l u m u C 1000000
y = -3,121x + 3,359,858
500000
0 0
500
1000
1500
Rate BPD
2000
2500
Two basic solutions • Find individual reservoir production from sources other than WOGCC • Estimate the pre 1978 production based on available WOGCC data.
Other comprehensive sources of information • WGA Symposiums - They usually published reservoir cums for the year in which the symposium was published • IHS - Although the production data is reported by well - by recombining the data it gives both the total reservoir production and the reservoir
production prior to 1978
Poor match with field cums WOGCC Total Field Cum
IHS Total Field Cum
(Basin)
Field
GGRB
BIRCH CREEK
GGRB
ARCH ( PATRICK DRAW)
GGRB
GREEN RIVER BEND
PRB
FIDDLER CREEK EAST
GGRB
HOGSBACK
GGRB
PATRICK DRAW
9,548,258
58,344,237
PRB
CLARETON
6,409,638
27,160,863
PRB
FIDDLER CREEK
5,861,157
26,807,558
PRB
LITTLE BUCK CREEK
120,372
9,425,596
PRB
SEMLEK SOUTHWEST
412,727
4,184,979
90,423,491 19,057,196 13,739,093 11,327,391 8,911,019
11,516,555 2,447,684 6,227,030 612,322 1,548,950
Poor match with reservoirs
Field
Formation
WOGCC Reservoir 1978-2009
IHS Reservoir 1978-2009
FOURBEAR
DARWIN-MADISON
1,207,599
425,237
FOURBEAR
DINWOODY
1,257,573
337,115
FOURBEAR
DINWOODYPHOSPHORIA-TENSLEEP
15,635
24,322
FOURBEAR
DINWOODY-PHOSPHORIA
FOURBEAR
DINWOODY-PHOSPHORIATENSLEEP-DARWIN-MADISON
FOURBEAR
MADISON
FOURBEAR
PHOSPHORIA
276,290
410,854
FOURBEAR
TENSLEEP
349,972
1,897,764
FOURBEAR
TENSLEEP-DARWIN-MADISON
0
183,800
47
3,160,816
3,023,756
6,065
When sources don’t match • When 2 of the 3 agree I generally use one of the two agreeing sources • When there is no agreement - I use WOGCC - it is the publically available data source To do this: – Assume relative amounts of production amongst reservoirs has remained constant. – Back calculate reservoir cums using proportional amounts of pre 1978 field cum.
Complications • Lack of pre 1978 WOGCC reservoir data • Engineering changes after a “steady
state” decline • Secondary vs. Tertiary recovery • Poor (or nonexistent ) decline • Terminology
Late change in decline after long “steady state” Tensleep Fm., Beaver Creek , WRB
ULTIMATE RECOVERY
USING S LOPE
4
slope =
-0.0031
x (last rate) =
3.5
112.8
y (last cum MMBO) =
O B 3 M M n 2.5 o i t c u d 2 o r P e v 1.5 i t a l u m 1 u C
y = -0.0031x + 3.3599
3.367973 y=ax+b y-(slope*x) = b
(MMBO) Ultimate by slope
0.5
0 0
500
1000
1500
Rate BPD
2000
2500
3.717743 3,717,743
Complications • Lack of pre 1978 WOGCC reservoir data • Engineering changes after a pseudosteady state decline • Secondary vs. Tertiary recovery • Poor (or nonexistent ) decline • Terminology
Secondary vs. Tertiary Recovery 3.5
3
y = -0.0025x + 2.9563 R² = 0.9121
2.5
Tertiary recovery EUR = 3,666,852 BO (Trend tacked on to last data point)
2
1.5
1
y = -0.0019x + 1.3654 R² = 0.5983
Secondary recovery EUR = 1,365,400 BO
0.5
0 0
100
200
300
400
500
600
Complications • Lack of pre 1978 WOGCC reservoir data • Engineering changes after a pseudosteady state decline • Secondary vs. Tertiary recovery • Poor (or nonexistent ) decline • Terminology
3.5
3.5 y = -0.0004x + 3.1717 R² = 0.9509
3
3
y = 0.0017x + 0.0991 R² = 0.8592
2.5 y = -0.0006x + 3.1942 R² = 0.7992
2.5 2 2
1.5 Series1
1.5
Linear (Series1)
1
0.5 1 0 0
0.5
0 0
500
1000
1500
2000
500
1000
1500
ULTIMATE RECOVERY USING SLOPE slope = -0.0005 x (rate) = 1090.649123 y (cum MMBLS) = 2.721578 y=ax+b y-(slope*x) = b 3.266903
Ultimate by slope
3,266,903
0.7
0.6
ULTIMATE RECOVERY USING SLOPE 0.5
slope = x (rate) =
0.4
y = -0.0009x + 0.1136
0.3
y = -0.0005x + 0.066
y (cum MMBLS) =
-0.0006 85 0.620213 y=ax+b y-(slope*x) = b 0.662713
y = -0.0005x + 0.0461
0.2
Ultimate by slope
0.1
0 0
50
100
150
662,713
0.3 ULTIMATE RECOVERY USING SLOPE slope =
0.25
-0.0012
x (rate) = y (cum MMBLS) =
0.2
45 0.276290 y=ax+b
0.15
y-(slope*x) = b 0.330290
0.1 Ultimate by slope 0.05
y = -0.0012x + 0.2565 R² = 0.5045
0 0 -0.05
100
200
300
330,290
1.4 y = -0.0006x + 1.3569
1.2
1 y = -0.001x + 1.1853
0.8
0.6
0.4 y = -0.0005x + 0.4129 0.2
0 0
100
200
300
400
500
600
700
All data (1978 to 2009)
Possible declines
0.5
0.5
0.45
0.45
0.4
0.4
O B 0.35 M M n o 0.3 i t c u d 0.25 o r p e v 0.2 i t a l u m0.15 u C
Last decline EUR = 426,300 BO
y = -0.0006x + 0.4263
0.35 0.3
Lowest point of three declines EUR = 681,200 BO
0.25 0.2 0.15
y = -0.0166x + 0.6812
All late data y = -0.0033x + 0.4449
EUR =
0.1
0.1
444,900 BO
0.05
0.05
0
0 0
20
40
60
Rate BPD
80
100
0
20
40
60
80
100
Complications • Lack of pre 1978 WOGCC reservoir data • Engineering changes after a pseudosteady state decline • Secondary vs. Tertiary recovery • Poor (or nonexistent ) decline • C hanges in Terminology
Terminology (production vs. time) Reservoirs reported individually
C ombined reservoir data
100000
100000
10000
Embar Phosphoria
1000
10000
1000
100
100
10
10
1
1 Jan-78
Series1
Jul-83
Dec-88
Jun-94
Dec-99
May-05
Nov-10
Jan-78
Jul-83
Dec-88
Jun-94
Dec-99
May-05
Nov-10
Summary • Graph the available WOGCC data • Choose a section of the graph that seems to represent a natural “pseudo-steady state” decline. • Derive the partial EUR from the graph. • Determine the amount of prior production and add that to the partial EUR for the actual Estimated Ultimate Recovery. • Calculate OOIP using 35% recovery factor • If the reservoir has undergone Tertiary Recovery – then also determine the Tertiary EUR
