Summary
This paper presents a simplified method of production forecasting for
tight/shale-gas reservoirs exhibiting extended periods of linear flow, without
the use of complex tools (e.g., analytical models or numerical models). The
method, which is applicable to hydraulically fractured vertical wells and
multifractured horizontal wells, is simple because it relies principally on a
plot of inverse rate vs. square root of time, and it is rigorous in that it is
based on the theory of linear flow and combines the transient linear-flow
period with hyperbolic decline during boundary-dominated flow.
The dominant flow regime observed in most tight/shale-gas wells is linear
flow, which may continue for several years. This linear flow will be followed
by boundary-dominated flow at later times. Therefore, the method proposed in
this study is applicable for forecasting production data for these wells
because it considers these two important flow regimes. The derivation is
presented for a hydraulically fractured well, and this simplified method can be
applied both to hydraulically fractured vertical wells and to horizontal wells
with multiple fractures. The application of this method to multifractured
horizontal wells in the Marcellus and Barnett shale gas is also presented.
The method is validated by comparing its results with test cases, which are
built using numerical simulation for hydraulically fractured vertical wells.
For each case, only the first year of the synthetic production data is then
used for the analysis. It is found that there is reasonable agreement between
the forecast rates obtained using this method and the numerically simulated
rates.
Currently, analysis techniques using material-balance time are being used in
industry to analyze tight/shale-gas reservoirs. Because material-balance time
is actually boundary-dominated flow superposition time, these analyses may show
symptoms of boundary-dominated flow even though the reservoir is still in
transient flow. The advantages of the forecasting method proposed in this study
are that: (1) it is not biased toward any flow regimes because no superposition
time functions are used; (2) reliable forecasts can be obtained without using
pseudotime--this is an advantage because using pseudotime introduces
complexities and an iterative procedure; and (3) the only major unknown is the
drainage area.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
20 May 2011
- Meeting paper published:
28 May 2010
- Revised manuscript received:
29 March 2012
- Manuscript approved:
19 May 2012
- Published online:
17 October 2012
- Version of record:
20 November 2012
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