Summary
Coalbed-methane (CBM) production in the San Juan basin of northwestern New
Mexico and southwestern Colorado has spanned more than 30 years. Some parts of
the field, such as the high-permeability Fairway, are now in a mature stage of
reservoir-pressure depletion. Optimization of well-production operations in the
Fairway presents many challenges because of its extremely low reservoir
pressure (less than 100 psi in some areas), heavy coal-fines production,
difficult artificial-lift challenges, increasing CO2%, and the
presence of paraffin, inorganic scale, and corrosion.
We use history matching by reservoir simulation to help diagnose the causes
of well-production inefficiencies and then plan how to mitigate them.
Simulation of Fairway wells typically require the use of an increasing
reservoir-permeability trend caused by coal-matrix shrinkage with the
desorption of methane and CO2. However, we have observed in some
Fairway wells that below a reservoir pressure of approximately 300 psi, there
is a flattening or even a decrease in the permeability trend. This shift in the
permeability trend is likely caused by coal failure (i.e., a change in
mechanical properties of coal) that is evidenced in the wells by an increased
amount of coal-fines production.
This paper is written in two parts. The first part presents the challenges
we face in operating Fairway wells and the solutions we have developed to
overcome them. Field observations and operating guidelines will be shared,
along with well-intervention histories where we have seen success. The second
part discusses our use of reservoir simulation to diagnose the causes of
reduced well-production efficiency.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
4 November 2010
- Meeting paper published:
21 September 2010
- Revised manuscript received:
3 March 2010
- Manuscript approved:
16 December 2010
- Published online:
25 March 2011
- Version of record:
16 May 2011
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