Summary
Recent advances in production data analysis (PDA) techniques have greatly
assisted engineers in extracting meaningful reservoir and stimulation
information from well-production and flowing-pressure data. Application of
these techniques to coalbed-methane (CBM) reservoirs requires the unique coal
storage and transport properties to be accounted for. In recent work, the
authors [ex. Clarkson et al. (2007a) and Jordan et al. (2006)] and others [ex.
Gerami et al. (2007)] have demonstrated how new techniques such as the flowing
material balance (FMB) and production type curves may be adapted to account for
CBM storage mechanisms (i.e., adsorption), but, to date, the focus has been on
relatively simple CBM reservoir behavior such as single-phase (gas) reservoirs
with static effective permeability.
The major contribution of the current work is the adaptation of modern PDA
techniques (by use of modified material balance time/pseudotime and
pseudopressure definitions) to analyze producing wells completed in CBM
reservoirs exhibiting several possible flow characteristics: single-phase flow
of gas in dry CBM reservoirs, single-phase flow of water (in undersaturated
reservoirs), and two-phase (gas and water) flow (in saturated reservoirs). The
latter reservoir type commonly exhibits effective permeability changes during
depletion (because of relative and/or absolute permeability changes) and
changing gas composition caused by relative adsorption effects, both of which
have been accounted for in the current work. Specifically, the FMB technique is
modified to include several complex CBM reservoir characteristics, and
production type curves are applied to some scenarios. Although dry-CBM-well
analysis was covered previously [ex. Clarkson et al. (2007a)], we will also
discuss FMB development in these reservoirs for completeness.
Several synthetic and field examples are given to demonstrate how FMB,
type-curve analysis, and analytical simulation can be used in parallel to
provide a particularly useful data-analysis toolset and workflow. These
techniques were used successfully to extract quantitative reservoir information
from single- and two-phase CBM-simulated and field-production pressure data.
The PDA techniques developed for two-phase CBM require further evaluation,
however.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
12 February 2007
- Meeting paper published:
16 April 2007
- Revised manuscript received:
17 August 2007
- Manuscript approved:
23 August 2007
- Version of record:
25 April 2008
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