6. “Overview of proposed method to calculate reserves
for conventional reservoirs and interpretation of case
study using Microsoft Excel and MBAL”
7. Identification
of hyperbolic
decline family
equation using
graphical
analysis
Predict the
future forecast
using hyperbolic
family equation
aided by
Fetkovich type
curve
We compared the
actual production
data and the
generated data and
studied the impacts
on our results.
We find out
declining rate
using the
corresponding
the hyperbolic
family equation
In the second part a
base model was
considered using
commercial available
software to replicate
one of the case
history using
Fetkovich type
curve.
11. Classical curve fit of historical production data
•Exponential Decline
•Harmonic Decline
•Hyperbolic Decline
Type-curve matching technique
•Fetkovich Type Curve
•Carter Type Curve
12. Arps’ Equation
q(t) =
qi
(1 + bDit)
1
b
Where,
b = Decline exponent t = Time, days
qi = Initial rate, Mscf/day Di = Initial decline rate, day-1
13.
14. Decline curves characterized by 3 factors:
Initial Production Rate
Curvature of decline
Rate of decline
Ikuko Analysis
Production must Have been stable
Stable reservoir conditions
DCA is used in evaluation of new investment
18. Based on analytical solutions
Can be used for analyzing hydraulically fractured wells
Include both flow regimes.
19. Plot q(t) & Gp (t) vs time on log-log paper
Match the production data to the best fitting type curve
Record the values of corresponding parameters.
40. 1
10
100
1000
0 2 4 6 8 10 12 14 16
FlowRate(Mscf/D)
Time (Year)
Past history of given data
41. 1
10
100
1000
0 10 20 30
FlowRate(Mscf/D)
Time (Year)
Past History
Future Forcast
1
10
100
1000
0 10 20 30
FlowRate(Mscf/D)
Time (Year)
Past History
Future Forcast
Mbal
Comparison of Past and Future Forecast by
“Microsoft Excel” using
Comparison of Past and Future Forecast by
“Mbal” using
Exponential
Decline Curve
cannot be applied
for this case
42. 1
10
100
1000
0 10 20 30
Rate(Mscf/D)
Time (Year)
Past History
Future Forecast
1
10
100
1000
0 10 20 30
Rate(Mscf/D)
Time (Year)
Past History
Future Forecast
Mbal
Comparison of Past and Future Forecast by
“Microsoft Excel” using
Comparison of Past and Future Forecast by
“Mbal” using
Harmonic Decline
Curve cannot be
applied for this
case
43. 1
10
100
1000
0 10 20 30
FlowRate(Mscf/D)
Time (Year)
Past History
Future Forecast
1
10
100
1000
0 5 10 15 20 25 30
FlowRate(Mscf/D)
Time (Year)
Past History
Future Forecast
Mbal
Comparison of Past and Future Forecast by
“Microsoft Excel” using
Hyperbolic Decline
Curve cannot be
applied for this
case
Comparison of Past and Future Forecast by
“Mbal” using
44. 1
10
100
1000
0 5 10 15 20 25 30
FlowRate(Mscf/D)
Time (Year)
Past History
Future Forecast
Comparison of Past and Future Forecast by
Fetkovich type
Curve be the most
feasible solution
for this case
46. •DCA can be applied on any type of reservoir whether it is gas reservoir or oil reservoir
with equal accuracy & whether it is conventional one or unconventional and we just
need past production history.
•While applying DCA for unconventional reserves just keep in mind the very low
permeability factor because our reservoir should be in the pseudo steady state.
•DCA can be used to estimate ultimate gas recovery, remaining productive life of the
field at some abandonment pressure, drainage radius and pore volume, skin &
permeability of the reservoir.
47. •DCA is much more accurate and requires less data as compared to the
MBE technique and volumetric technique, since it predicts future
forecast using past production history and it accommodates the time
factor as well, i.e. how much time this reservoir will take to recover this
amount of reserves and in petroleum sector “time is money”.
48. •DCA can be applied only if the past production trends follows one of the “Hyperbolic
family of equations i.e. exponential, hyperbolic or harmonic trends”, if it is not
happening, we cannot estimate reserves in an effective way.
•DCA can only give precise future estimates if production controlling factors will
continue in the future following the past trends & production mechanism will remains
same e.g. if we install artificial lift system on a reservoir after DCA estimation, in that
case DCA results becomes erroneous.
49. •Utilize all available techniques:
Utilizes curve matching technique as well other than hyperbolic equations for
high effective results.
•Comparison between the data base and software base:
Use of data base and compares their results with commercial available
software to estimates better reserves.
•Utilize modern techniques for unconventional reservoirs:
Use of modern techniques like “Exponental+Hyperbolic decline” & “Power
exponential decline” for unconventional reservoirs etc.
Decline type curves are the theoretical plots of solution to flow equations. Decline type curves have been developed so that actual production data can be matched without special graph paper.
Type curve methods use log-log graph paper to match pre-plotted theoretical solutions with actual production data. Further, type-curve analyses allow us to estimate not only original gas in place but also the flowing characteristics of individual wells.
The Fetkovich decline type curves are based on analytical solutions to the flow equations for production at constant BHP from a well centered in a circular reservoir or drainage area with no-flow boundaries. The type curves in Fig. include both transient or infinite-acting and boundary-dominated flow regimes. These curves can also be used for hydraulically fractured reservoirs for taking long term gas production data.
Fetkovitch type curves are developed in terms of dimensionless variables. For flow rate vs. time plot it uses dimensionless flow rate & time.
l. Plot q(t ) and Gp(t) vs. t on log-log paper (3-in. log cycles) or tracing paper with the same size logarithmic cycles as the Fet kovich type curve.
2-Match the cumulative production data to the best-fitting type curve. Note that the cumulative production data plot often is much smoother than the rate plot and therefore is easier to match to de termine the Arps decline constant.
3-Record values of the correlating parameters for transient and boundary-dominated flow (i.e., relrwa and b, respectively) from the match of the cumulative production data.
Decline-curve methods provide a method for estimating original gas in place and ultimate recoveries at some abandonment condition from a well or an en tire field. In addition, decline curves can be used to estimate future production and productive life. However, decline-curve analysis techniques have several important limitations.
Recall that the Fetkovich type curves were generated with the assumption that the well is produced at a constant BHP. Further, the type curves assume that k and s remain constant with time. Any changes in field development strategies or production operation prac tices, however, could change the production trends of a well and significantly affect reserve estimates from decline-curve techniques.
the basis of decline type-curve analysis is the as sumption that boundaries affect the rate response. If true boundary dominated flow is not established, then there is no theoretical ba sis for decline-curve methods and predictions of future production may be inaccurate.
Finally, decline-curve analysis assumes a volumetric reservoir i.e., a closed reservoir that receives no energy from external sources
Any changes in well development patterns or production operations can change the drainage volume of a well and affect the decline behavior.
From about 1975 to 2005, various methods have been developed for estimating reserves in tight gas reservoirs.
Fetkovich (1980) proposed a widely accepted decline curve analysis method using a set of type curves. He extended the original work of Arps
Holditch and Madani (2010) highlighted that worldwide gas resources from conventional reservoirs are diminishing with unconventional reservoirs playing more important roles in sustaining production to satisfy energy consumption demand. They classified unconventional gas resources into the three most common types: tight sands, coal bed methane, and shale gas.
Naik (2013) gave examples of authors that referred to tight gas with different cutoffs. These are basically the employing modified DCA techniques used to compute reserves in the conventional and unconventional reserves and thus analyze the future forecast.
