New Decline Curve Tool for
GOM3/GOMsmart &
“Forgotten Oil & Gas Study”
2012 GOM3 User Conference at Anadarko
John D. Grace, Ph.D.
Earth Science Associates
New Tool Objectives
• Provide a robust tool for forecasting
production & estimating remaining resources
by completion/completion interval
• Introduce optional new method for refining
decline curve analysis accounting for “breaks
in regime”
• Internally, use tool in batch mode to identify
opportunities for further production
Decline Curves
• Use regression analysis to forecast a
production series beyond the last observation
• With forecast “integrate under the curve” for
remaining resources ≥ abandonment level
• Use confidence intervals on regression to
estimate confidence intervals on remaining
• Use analysis of breaks in time series to
improve on “naïve” regression models
Stereotypical Decline Curve
Oil Production
Barrels per day
400
300
200
100
1
2
3
Years on Production
4
Fitting a Decline Curve
• Classical functional forms of decline curves
– Exponential (rate vs. time)
– Hyperbolic (rate vs. time)
– Linear (rate vs. cumulative production)
– P/Z vs. cumulative production (gas only)
• Where does the estimable decline start?
– Global maximum production rate?
– At the last significant structural break in regime?
Exponential Decline Model
y  aebx
Hyperbolic Decline Model
q
q0
(1  kb0t )
1
k
Linear Decline Model
y  a  bx
(P/Z) Linear Model
y  a  bx
Improving & Choosing Model
• Statistical measures of “goodness of fit”
– R2 and “predicted R2”
– Statistics on estimated parameter of decline
– Still under research (e.g., retrospective forecast)
• Actuarial approach (cum. prob. den. function)
• Optimal choice of structural break
– Last break – problem of shutting down well
– Compare candidate breaks (& forms) against cdfs
– Allow user to chose break point
Actuarial Approach to EUR
Cumulative Prob.
Oil
Gas
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
0
2
4
Million bbls
6
0
10
20
30
BCF
40
50
Conditioning Variables: Drilling date, perf thickness, geologic age, reservoir volume,
reservoir permeability, GOR, oil viscosity, gas specific gravity,
reservoir drive mechanism, operator (?)
Exploiting Structural Break in Regime
Global Max
Default:
We find
break
Option:
You set
break
Terminal
Regime
Break
Adding Water to Analysis
Tool Interface (in GOMsmart)
Tool looks the same in GOM3 & the GOMsmart Map but is called
from the Hot Link Tool
Tool Output
Charts
Reports
Excel Download
“Forgotten Oil & Gas Study”
• Motivated by running Decline Curve Tool in
batch mode
– ~60,000 completions/ completion intervals
– Sensitivities to abandonment rate