Decline Curve Analysis Course
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Reservoir Engineering
Chapter 12 – Decline Curve Analysis Arron Singhe
2000 oil rate Expon. (oil rate)
Oil Rate
1500 y = 1784.5e-0.0503x 1000
500
0 0
10
Time
20
30
Introduction Decline Curve Analysis
INTRODUCTION
OUTLINE
BACKGROUND TYPES OF DECLINE CURVES
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DECLINE CURVE ANALYSIS (DCA)
2
Introduction Decline Curve Analysis A Property Status
B Pre-drilling Period
INTRODUCTION
D
Well Completed
Study Method
E
F
Production Operations Abandonment
Development Period
BACKGROUND TYPES OF DECLINE CURVES
C 1st
Analog
Volumetric
Performance Simulation Studies Material Balance Studies Decline Trend Analyses
APPLICATION OF DCA
Range of Estimates
Ultimate Recovery
Actual Recovery Range of Recovery Estimates
Production Profile
Cumulative Production
Log Production Rate
Cumulative Rate
Time
Relative Risk
Risk
High
Low
3
A
B
C
D
E
F
Introduction Decline Curve Analysis
INTRODUCTION
INTRODUCTION
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
What is decline curve analysis?
–
Decline Curve Analysis (DCA) is a simple, graphical method that uses extrapolation of performance trends to obtain
• • •
the remaining oil reserves the ultimate oil recovery or the remaining production life of a well, field, etc.
2000 oil rate Expon. (oil rate)
Oil Rate
1500 y = 1784.5e-0.0503x 1000
500
0 0
4
10
Time
20
30
Introduction Decline Curve Analysis
INTRODUCTION
INTRODUCTION
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
What is decline curve analysis?
– – –
5
A curve fit of the past production performance is done using certain standard curves. This curve fit is then extrapolated to predict future performance and to estimate recoverable reserves Conventional Decline Curve Analysis can be used only when the production history is long enough that a trend can be identified.
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The basic assumption: – Whatever causes controlled the trend of a curve in the past will continue to govern its trend in the future in a uniform manner
– The extrapolation procedure is therefore of empirical nature – The reserve estimates obtained by DCA are limited to those recoverable under the existing conditions DCA cannot be applied across recovery phases – e.g. initiating a water-flood would definitely change the causes that controlled the trend of the curve too much
– DCA should be applied for reservoirs under boundary restricted flow conditions
6
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
7
Restrictions – This method is not based on physical principles – It can only be applied as long as the mechanical conditions of the well (completions, production method, ...) are not changed – Assumes that the driving forces in the reservoir are not changed during the time.
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The instantaneous or current decline rate – which is a continuous function that is used in the mathematical derivation of the decline curve
–
it is the negative slope of the curve (log q) vs. time and hence defined as
D
–
8
d ln q dq / q dt dt
D is the decline rate expressed in “% per year”.
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Three types of curves have been identified: – Exponential – Hyperbolic – Harmonic It is implicitly assumed that the factors causing the decline continue, unchanged, during the forecast period. – Reservoir conditions – Operating conditions
9
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Exponential Decline (Constant Percentage Decline) – the nominal decline rate D is a constant
D
d ln q dq / dt const dt q
– which after integration leads to: t
q
0
qi
Ddt d ln q Dt ln q ln qi q qi e Dt
– Plotting q versus log(time) will give a straight line with slope D
10
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Harmonic Decline – the nominal decline rate D is proportional to the production rate (i.e. it is a special case of the hyperbolic decline where b = 1)
D
dq / dt Kq q
– which after integration leads to: q
qi 1 Di t
– where Di is the initial nominal decline and K is a constant which can be determined under initial conditions
K
11
Di qi
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Hyperbolic Decline – the nominal decline rate D is proportional to a fractional power b of the production rate
D
dq / dt Kq b q
– which after integration leads to: q qi 1 bDi t
1/ b
– where Di is the initial nominal decline and K is a constant which can be determined under initial conditions.
K
12
Di qi
Introduction Decline Curve Analysis
INTRODUCTION BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
13
TYPES OF DECLINE CURVES
Introduction Decline Curve Analysis
INTRODUCTION
FLOW RATE COMPARISON
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Relationships for production rates: – exponential decline (n = 0)
qt qi e Dt
–
hyperbolic decline (0<= n <= 1)
qt qi 1 nDi t
1 / n
–
harmonic decline (n = 1)
qt
14
qi 1 Di t
Introduction Decline Curve Analysis
INTRODUCTION
CUMULATIVE PRODUCTION COMPARISON
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Relationships for cumulative production with rate: – exponential decline (n = 0)
qi qt Np D
–
hyperbolic decline (0<= n <= 1) n 1 qi qi Np 1 n 1 Di qt
–
harmonic decline (n = 1)
qi qi Np ln Di qt 15
Introduction Decline Curve Analysis
INTRODUCTION
PRINCIPAL EQUATIONS - OVERVIEW
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Type n Rate
Hyperbolic
Harmonic
0
1
qt qi 1 nDi t
1 / n
qt qi e Dt
qt
qi 1 Di t
Cum. Prod q qt Np i with rate D
q n 1 q q qi Np i 1 N p i ln i Di n 1 Di qt qt
Cum Prod q N p i 1 e Dt D with time
Np
Prod. time
16
Exponential
1 q t ln i D qt
qi n 1 Di
n 1 1 nDi t n 1
n 1 qi t 1 nDi qt
Np
t
qi ln1 Di t Di
1 qi 1 Di qt
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
DCA is mainly used for – production forecasting and – reserve estimation during primary production DCA can be applied to basically any well and any reservoir because – it is solely based on production data and – production data is the only data that is always available
17
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
– DCA has been used since the 1920s. Back then the evaluation was purely graphical. Nowadays DCA is applied with the help of – curve fitting tools in spreadsheet programs or – whole DCA modules in production database programs Advanced DCA features in today’s production databases greatly speed up the application – e.g. auto decline fitting Furthermore is it possible to evaluate multiple performance trends – e.g. oil production vs. time and water cut vs. cumulative production is extrapolated to a minimum oil rate and a maximum water cut, whichever is reached first
18
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The two main types of curves used for DCA are: – rate vs. time – rate vs. cumulative production Other type of curves that are also applied, but mostly in a secondary manner (i.e. as a measure to determine when the economic limit is reached): – water cut vs. time – water cut vs. cumulative production – water rate vs. time etc.
19
Introduction Decline Curve Analysis
EXAMPLE 12.1
INTRODUCTION BACKGROUND
The following DCA has been fitted to the well production data – Oil rate in STB/d, cum. Oil in STB – Time in months
TYPES OF DECLINE CURVES APPLICATION OF DCA
0.6
10000
oil rate Expon. (oil rate) 0.5
0.4
Water Cut
Oil Rate
y = 1796.4e-0.0479x
y = 7E-05x - 1.6023
1000
0.3
0.2
0.1
0
100 0
5
10
15
20 Time
20
25
30
35
0
5000
10000
15000
20000
Cum ulative Oil Production
25000
30000
3500
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.1
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
1. What type of decline is it ? 2. What is the nominal decline D ? 3. When is the economic limit of 100 bbl/d reached ? 4. What is the estimated ultimate recovery for this economic limit ? 5. What is the estimated ultimate recovery if a water cut of 0.9 is used as the economic limit ?
6. What is the estimated ultimate recovery if both economic limits are considered ?
21
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE - ANSWERS
BACKGROUND TYPES OF DECLINE CURVES
1. What type of decline is it ? exponential decline
APPLICATION OF DCA
2. What is the nominal decline D ? the nominal decline is given from the decline curve, D = 0.0479 or 4.8 % per month
3. When is the economic limit of 100 bbl/d reached ? q 1796.4e0.0479t t
22
1 100 ln 60.3 months 0.0479 1796.4
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE - ANSWERS
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
4. What is the estimated ultimate recovery for this economic limit ? qi q 1796.4 100 30.417 1077220bbl D 0.0479 5. What is the estimated ultimate recovery if a water cut of 0.9 is used as the economic limit ? the curve fit gave the following equation N p max
watercut 7 105 (cum.oil ) 1.6023
N p max
0.9 1.6023 7 10
5
35747 bbl
6. What is the estimated ultimate recovery if both economic limits are considered ? It is the smaller one of the two, therefore Npmax = 35747 bbl
23
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.2
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
24
Given the following production history
– –
What type of decline is this? Estimate D and b!
Time [Months]
Rate [STB/day]
0
350
1
345
2
340
3
335
4
330
5
325
6
320
7
315
8
310
9
306
10
301
11
297
12
292
13
288
14
284
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.3
BACKGROUND TYPES OF DECLINE CURVES
–
A well with an exponential decline of 0.01 [1/month] produces at 150 STB/day
APPLICATION OF DCA
– – –
25
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.4
BACKGROUND TYPES OF DECLINE CURVES
–
A well with a harmonic decline of 0.01 [1/month] produces at 150 STB/day
APPLICATION OF DCA
– – –
26
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.5
BACKGROUND TYPES OF DECLINE CURVES
–
A well with a hyperbolic decline of 0.01 [1/month] and n = 0.6 produces at 150 STB/day
APPLICATION OF DCA
– – –
27
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.6
BACKGROUND TYPES OF DECLINE CURVES
–
APPLICATION OF DCA
– – –
28
The AX-1 reservoir has been producing oil for over 30 years from the Bartlesville (Oklahoma) sands at a depth of 300 - 400 m. Between 1985 and 1988, 42 wells were on production. The field can be operated economically as long as production is in excess of 1 m3/day per well. Eight in-fill wells were drilled in early 1989, and another 25 wells were stimulated with acid. This resulted in an increase in oil production. The following table is a record of the daily production from the reservoir between January 1985 and December 1989. Determine what the incremental cumulative production would be at reservoir abandonment following the drilling of the in-fill wells and the stimulation of the others.
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.6
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
1985-Jan. April July Oct. 1986-Jan. April July Oct. 1987-Jan. April July Oct. 1988-Jan. April July Oct. 1989-Jan. April July Oct. Dec. 29
Time [Months] 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Wells on production 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 50 50 50 50 50
Oil rate [m 3 /day] 210 198 187 177 167 157 149 141 133 125 118 112 106 100 94 89 150 136 124 113 103
Chapter 12 – Decline Curve Analysis Arron Singhe
2000 oil rate Expon. (oil rate)
Oil Rate
1500 y = 1784.5e-0.0503x 1000
500
0 0
10
Time
20
30
Introduction Decline Curve Analysis
INTRODUCTION
OUTLINE
BACKGROUND TYPES OF DECLINE CURVES
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DECLINE CURVE ANALYSIS (DCA)
2
Introduction Decline Curve Analysis A Property Status
B Pre-drilling Period
INTRODUCTION
D
Well Completed
Study Method
E
F
Production Operations Abandonment
Development Period
BACKGROUND TYPES OF DECLINE CURVES
C 1st
Analog
Volumetric
Performance Simulation Studies Material Balance Studies Decline Trend Analyses
APPLICATION OF DCA
Range of Estimates
Ultimate Recovery
Actual Recovery Range of Recovery Estimates
Production Profile
Cumulative Production
Log Production Rate
Cumulative Rate
Time
Relative Risk
Risk
High
Low
3
A
B
C
D
E
F
Introduction Decline Curve Analysis
INTRODUCTION
INTRODUCTION
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
What is decline curve analysis?
–
Decline Curve Analysis (DCA) is a simple, graphical method that uses extrapolation of performance trends to obtain
• • •
the remaining oil reserves the ultimate oil recovery or the remaining production life of a well, field, etc.
2000 oil rate Expon. (oil rate)
Oil Rate
1500 y = 1784.5e-0.0503x 1000
500
0 0
4
10
Time
20
30
Introduction Decline Curve Analysis
INTRODUCTION
INTRODUCTION
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
What is decline curve analysis?
– – –
5
A curve fit of the past production performance is done using certain standard curves. This curve fit is then extrapolated to predict future performance and to estimate recoverable reserves Conventional Decline Curve Analysis can be used only when the production history is long enough that a trend can be identified.
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The basic assumption: – Whatever causes controlled the trend of a curve in the past will continue to govern its trend in the future in a uniform manner
– The extrapolation procedure is therefore of empirical nature – The reserve estimates obtained by DCA are limited to those recoverable under the existing conditions DCA cannot be applied across recovery phases – e.g. initiating a water-flood would definitely change the causes that controlled the trend of the curve too much
– DCA should be applied for reservoirs under boundary restricted flow conditions
6
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
7
Restrictions – This method is not based on physical principles – It can only be applied as long as the mechanical conditions of the well (completions, production method, ...) are not changed – Assumes that the driving forces in the reservoir are not changed during the time.
Introduction Decline Curve Analysis
INTRODUCTION
THEORETICAL BACKGROUND
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The instantaneous or current decline rate – which is a continuous function that is used in the mathematical derivation of the decline curve
–
it is the negative slope of the curve (log q) vs. time and hence defined as
D
–
8
d ln q dq / q dt dt
D is the decline rate expressed in “% per year”.
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Three types of curves have been identified: – Exponential – Hyperbolic – Harmonic It is implicitly assumed that the factors causing the decline continue, unchanged, during the forecast period. – Reservoir conditions – Operating conditions
9
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Exponential Decline (Constant Percentage Decline) – the nominal decline rate D is a constant
D
d ln q dq / dt const dt q
– which after integration leads to: t
q
0
qi
Ddt d ln q Dt ln q ln qi q qi e Dt
– Plotting q versus log(time) will give a straight line with slope D
10
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Harmonic Decline – the nominal decline rate D is proportional to the production rate (i.e. it is a special case of the hyperbolic decline where b = 1)
D
dq / dt Kq q
– which after integration leads to: q
qi 1 Di t
– where Di is the initial nominal decline and K is a constant which can be determined under initial conditions
K
11
Di qi
Introduction Decline Curve Analysis
INTRODUCTION
TYPES OF DECLINE CURVES
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Hyperbolic Decline – the nominal decline rate D is proportional to a fractional power b of the production rate
D
dq / dt Kq b q
– which after integration leads to: q qi 1 bDi t
1/ b
– where Di is the initial nominal decline and K is a constant which can be determined under initial conditions.
K
12
Di qi
Introduction Decline Curve Analysis
INTRODUCTION BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
13
TYPES OF DECLINE CURVES
Introduction Decline Curve Analysis
INTRODUCTION
FLOW RATE COMPARISON
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Relationships for production rates: – exponential decline (n = 0)
qt qi e Dt
–
hyperbolic decline (0<= n <= 1)
qt qi 1 nDi t
1 / n
–
harmonic decline (n = 1)
qt
14
qi 1 Di t
Introduction Decline Curve Analysis
INTRODUCTION
CUMULATIVE PRODUCTION COMPARISON
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Relationships for cumulative production with rate: – exponential decline (n = 0)
qi qt Np D
–
hyperbolic decline (0<= n <= 1) n 1 qi qi Np 1 n 1 Di qt
–
harmonic decline (n = 1)
qi qi Np ln Di qt 15
Introduction Decline Curve Analysis
INTRODUCTION
PRINCIPAL EQUATIONS - OVERVIEW
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
Type n Rate
Hyperbolic
Harmonic
0
1
qt qi 1 nDi t
1 / n
qt qi e Dt
qt
qi 1 Di t
Cum. Prod q qt Np i with rate D
q n 1 q q qi Np i 1 N p i ln i Di n 1 Di qt qt
Cum Prod q N p i 1 e Dt D with time
Np
Prod. time
16
Exponential
1 q t ln i D qt
qi n 1 Di
n 1 1 nDi t n 1
n 1 qi t 1 nDi qt
Np
t
qi ln1 Di t Di
1 qi 1 Di qt
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
DCA is mainly used for – production forecasting and – reserve estimation during primary production DCA can be applied to basically any well and any reservoir because – it is solely based on production data and – production data is the only data that is always available
17
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
– DCA has been used since the 1920s. Back then the evaluation was purely graphical. Nowadays DCA is applied with the help of – curve fitting tools in spreadsheet programs or – whole DCA modules in production database programs Advanced DCA features in today’s production databases greatly speed up the application – e.g. auto decline fitting Furthermore is it possible to evaluate multiple performance trends – e.g. oil production vs. time and water cut vs. cumulative production is extrapolated to a minimum oil rate and a maximum water cut, whichever is reached first
18
Introduction Decline Curve Analysis
INTRODUCTION
APPLICATION OF DCA
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
The two main types of curves used for DCA are: – rate vs. time – rate vs. cumulative production Other type of curves that are also applied, but mostly in a secondary manner (i.e. as a measure to determine when the economic limit is reached): – water cut vs. time – water cut vs. cumulative production – water rate vs. time etc.
19
Introduction Decline Curve Analysis
EXAMPLE 12.1
INTRODUCTION BACKGROUND
The following DCA has been fitted to the well production data – Oil rate in STB/d, cum. Oil in STB – Time in months
TYPES OF DECLINE CURVES APPLICATION OF DCA
0.6
10000
oil rate Expon. (oil rate) 0.5
0.4
Water Cut
Oil Rate
y = 1796.4e-0.0479x
y = 7E-05x - 1.6023
1000
0.3
0.2
0.1
0
100 0
5
10
15
20 Time
20
25
30
35
0
5000
10000
15000
20000
Cum ulative Oil Production
25000
30000
3500
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.1
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
1. What type of decline is it ? 2. What is the nominal decline D ? 3. When is the economic limit of 100 bbl/d reached ? 4. What is the estimated ultimate recovery for this economic limit ? 5. What is the estimated ultimate recovery if a water cut of 0.9 is used as the economic limit ?
6. What is the estimated ultimate recovery if both economic limits are considered ?
21
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE - ANSWERS
BACKGROUND TYPES OF DECLINE CURVES
1. What type of decline is it ? exponential decline
APPLICATION OF DCA
2. What is the nominal decline D ? the nominal decline is given from the decline curve, D = 0.0479 or 4.8 % per month
3. When is the economic limit of 100 bbl/d reached ? q 1796.4e0.0479t t
22
1 100 ln 60.3 months 0.0479 1796.4
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE - ANSWERS
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
4. What is the estimated ultimate recovery for this economic limit ? qi q 1796.4 100 30.417 1077220bbl D 0.0479 5. What is the estimated ultimate recovery if a water cut of 0.9 is used as the economic limit ? the curve fit gave the following equation N p max
watercut 7 105 (cum.oil ) 1.6023
N p max
0.9 1.6023 7 10
5
35747 bbl
6. What is the estimated ultimate recovery if both economic limits are considered ? It is the smaller one of the two, therefore Npmax = 35747 bbl
23
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.2
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
24
Given the following production history
– –
What type of decline is this? Estimate D and b!
Time [Months]
Rate [STB/day]
0
350
1
345
2
340
3
335
4
330
5
325
6
320
7
315
8
310
9
306
10
301
11
297
12
292
13
288
14
284
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.3
BACKGROUND TYPES OF DECLINE CURVES
–
A well with an exponential decline of 0.01 [1/month] produces at 150 STB/day
APPLICATION OF DCA
– – –
25
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.4
BACKGROUND TYPES OF DECLINE CURVES
–
A well with a harmonic decline of 0.01 [1/month] produces at 150 STB/day
APPLICATION OF DCA
– – –
26
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.5
BACKGROUND TYPES OF DECLINE CURVES
–
A well with a hyperbolic decline of 0.01 [1/month] and n = 0.6 produces at 150 STB/day
APPLICATION OF DCA
– – –
27
What will the production rate be in 2 years? What will the cumulative production be in those 2 years? How long will it take to reach the economic limit of 10 STB/day?
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.6
BACKGROUND TYPES OF DECLINE CURVES
–
APPLICATION OF DCA
– – –
28
The AX-1 reservoir has been producing oil for over 30 years from the Bartlesville (Oklahoma) sands at a depth of 300 - 400 m. Between 1985 and 1988, 42 wells were on production. The field can be operated economically as long as production is in excess of 1 m3/day per well. Eight in-fill wells were drilled in early 1989, and another 25 wells were stimulated with acid. This resulted in an increase in oil production. The following table is a record of the daily production from the reservoir between January 1985 and December 1989. Determine what the incremental cumulative production would be at reservoir abandonment following the drilling of the in-fill wells and the stimulation of the others.
Introduction Decline Curve Analysis
INTRODUCTION
EXAMPLE 12.6
BACKGROUND TYPES OF DECLINE CURVES APPLICATION OF DCA
1985-Jan. April July Oct. 1986-Jan. April July Oct. 1987-Jan. April July Oct. 1988-Jan. April July Oct. 1989-Jan. April July Oct. Dec. 29
Time [Months] 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Wells on production 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 50 50 50 50 50
Oil rate [m 3 /day] 210 198 187 177 167 157 149 141 133 125 118 112 106 100 94 89 150 136 124 113 103
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