Review of Research Efforts in Coalbed Methane Recovery
- R.S. Metcalfe (Amoco Production Co.) | D. Yee (Amoco Production Co.) | J.P. Seidle (Amoco Production Co.) | R. Puri (Amoco Production Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Asia-Pacific Conference, 4-7 November, Perth. Australia
- Publication Date
- Document Type
- Conference Paper
- 1991. Society of Petroleum Engineers
- 3 Production and Well Operations, 5.8.6 Naturally Fractured Reservoir, 5.5.8 History Matching, 5.3.1 Flow in Porous Media, 5.1.5 Geologic Modeling, 5.6.4 Drillstem/Well Testing, 3.1.5 Plunger lift, 1.10 Drilling Equipment, 5.6.3 Pressure Transient Testing, 4.6 Natural Gas, 4.5 Offshore Facilities and Subsea Systems, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.2.1 Phase Behavior and PVT Measurements, 5.3.2 Multiphase Flow, 5.8.3 Coal Seam Gas, 1.6 Drilling Operations, 5.5 Reservoir Simulation, 4.3.4 Scale, 5.4 Enhanced Recovery, 1.2.3 Rock properties, 1.6.9 Coring, Fishing
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The production of coalbed methane in the United States dates back to the early 1930's. Yet it was not until the early 1980's that research and development projects began to show the enormous potential of this projects began to show the enormous potential of this energy resource. These efforts have resulted in the rapid commercialization of coalbed methane production in the United States, including the drilling of almost 800 wells by Amoco. Efforts to evaluate and implement coalbed methane recovery projects are continuing, with current emphasis being placed on worldwide resources.
In recent months, we (and our colleagues) have published almost a dozen papers on coalbed methane published almost a dozen papers on coalbed methane production encompassing a wide variety of topics. This production encompassing a wide variety of topics. This paper summarizes the significant findings of those papers paper summarizes the significant findings of those papers and stresses their importance to field operations. Subjects covered include reservoir modeling, pressure transient analysis, rock property measurements, well stimulation, and enhanced coalbed methane recovery. Although most of the work discussed here was done on coals from the San Juan (Colorado and New Mexico) and Warrior (Alabama) Basins, the results are general and applicable to coals in other parts of the world.
Amoco Production Company began to investigate the potential of gas from coal in 1974. Initial results indicated that a significant volume of methane was adsorbed to coal in keeping with the same conclusions reached by the United States Bureau of Mines. We drilled our first commercial well, the Cahn No. 1, in the San Juan Basin of the United States (northwestern corner of New Mexico) in 1977. Initially, this well produced substantial water, little gas, and was plagued produced substantial water, little gas, and was plagued with operational problems due to coal fines. It was not until 1979 that engineers demonstrated that dewatering of coal wells was required before gas could be desorbed. After that breakthrough in production operations, it was relatively easy to get approval to expand operations at this location as well as into other basins; and the modern era of coalbed methane production began.
Since that time, we have been conducting laboratory experiments, evaluating field performance and running numerical simulation studies to improve our ability to monetize this resource. This paper provides a summary of our experience over the last 10 years as well as an indication of some of the areas that we are currently studying. The paper is broken into three subtopics: Gas Content, Recovery Processes and Reservoir Engineering. In the first subsection we discuss our philosophy of determining gas-in-place. The second subsection presents our views on how to maximize recovery from coal wells. The final subsection discusses applications of various reservoir engineering tools to better define rate and recovery potentials.
The first step in evaluating a potential coal play is determining gas content. Not only must coal be present, but also that coal must be of the right rank to contain adequate adsorbed gas for a good reserve position and have sufficient permeability to permit production at economic rates. We will speak first to the question of evaluating the gas content.
Gas is stored in coal as an adsorbed phase which is in a near liquid-like state as opposed to a free gas phase. This makes the estimation of gas-in-place different from conventional gas reservoirs. The gas in coal is usually expressed in terms of gas content and gas-in-place can be calculated from:
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