SPE Members Abstract The traditional concept of coalbed methane production is one where the coal natural fracture system is initially 100% saturated with water and that this water must be produced to initiate gas production. This paper summarizes an investigation designed to reconcile measured relative permeability data with well test analysis results obtained during single-phase and multi-phase tests, and with reservoir simulation projections of gas and water deliverability as a function of bottom-hole pressure. Improved well test and relative permeability measurement procedures are summarized so that projections of future fluid deliverability made during the dewatering and early multi-phase production stages are more accurate. A variety of well tests were performed that included water slug tests, water injection tests, gas injection tests, and multi-phase production and shut-in tests. Estimates of absolute permeability obtained from these data were variable depending upon the test procedures. In addition, multi-phase and gas injection test analyses were strongly influenced by the relative permeability data used during the analysis. Based upon newly measured relative permeability data and by history matching multi-phase production data, it was possible to reconcile some of the differences in estimates of absolute permeability that were obtained from each of the test types. Finally, a new field procedure is proposed and demonstrated to measure permeability in wells producing both water and gas. Introduction The understanding and modeling of methane production from Coal bed Methane (CBM) wells has proven to be a particularly challenging task for the gas industry. Unlike conventional gas wells where the production is typically modeled as single phase gas flow, CBM wells require that water be produced to reduce lower reservoir pressure below the desorption pressure so that gas can be produced. A thorough understanding of relative permeability is necessary in order to predict gas and water production rates. Typically, most well tests are initially conducted when the reservoir is water saturated so that single phase analysis techniques can be used to evaluate permeability. Unfortunately, there are far too many cases where the initial measured water permeability did not predict the eventual gas flow rates. In order to study all aspects of CBM production, the Gas Research Institute, in conjunction with Taurus Exploration, has operated the Rock Creek Methane from Multiple Coal Seams pilot production site at Rock Creek in the Black Warrior Basin for the last 10 years. Here the required well tests have been conducted and field data, including production data, has been collected in a controlled manner so an understanding of CBM could be developed. P. 313

This paper was selected for presentation by an SPE Prognun Committee following review of information contained in an abstract submitted by tho autbor(s). Contents of tho paper, as presented, have not been reviewed by tho Society of Petroleum. Engineers and are subjected to oorrcction by tho autbor(s). The material, as presented does not neoessarily reflect any position of tho Society of Petroleum. Engineers, its offioers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of tho Society of Petroleum. Engineers. Permission to ropy is restricted to an abstract of not more than 300 words. lliustrations my not be oopied. The abstract sboold oontain OOI18piC\lOU8 acknowledgement of where and by whom tho paper was presented. WriteLibrarian, SPE, P.O. Box 833836, Richardson, TX75083-3836, U.S.A., fax 01-214-952-9435. AbstractThis paper presents the first field scale measurements of insitu stress effects on permeability of coal seams. The importance of these effects on a highly compressible reservoir such as coal is demonstrated by relating permeability and production to stress.Well testing complications and the implications of stress toward exploitation of existing reserves and exploration for new reserves are also discussed. Additionally, comparisons of this paper's findings to prior theoretical work, core testing, and limited field data are presented.

The objective of two separate fracture treatment experiments performed in the Oak Grove Field, Alabama, was to estimate fracture geometry and effectiveness.

A new method for performing reduced cost injection/falloff tests in under-pressured reservoirs has been developed at the GRI sponsored Rock Creek research site. The new method referred to as the "Tank Test" uses gravity drainage from a water storage tank to inject water into the reservoir. The primary advantages of Tank Test over the traditional injection/falloff tests are reduced costs and improved test results. The tank test eliminates the need for expensive pumping equipment and the manpower required for manual pump rate adjustments. Further cost savings can also be made by using gauges intended for ground water monitoring in place of oil field gauges when downhole shutin is not required. The low cost of the Tank Test allows longer duration tests to be economically performed so that the radius of investigation of a test is extended. The Tank Test also reduces the possibility of fracturing the reservoir during the injection portion of the test which is a common problem when testing shallow low permeability reservoirs. This paper describes the circumstances under which the Tank Test is most applicable, the equipment that is required and how to perform the test. The paper presents results of field tests performed on coal seams and a test performed on an Antrim Shale well. A simple Tank Test design procedure is also provided.

Since 1984, the Gas Research Institute has been conducting field evaluations of coalbed methane technology at the Rock Creek Project site near Birmingham, Alabama. This paper presents and discusses preliminary conclusions based on initial reservoir engineering analysis of data gathered from field experiments performed at Rock Creek..M~jor conclusions from the analysis performed to date are 1) post shut-rn methane production is not significantly reduced by water Influx during normal shut-in periods, 2) long-term methane recovery fro~ ~.well is ~ot a function of initial water pumping rate, provided the 1nrt1al rate IS a~ove the minimum required to initiate desorption, and 3) well-to-well rnterference is the primary mechanism for efficient recovery of coalbed methane.Ongoing reservoir engineering analysis will provide further insights toward characterizing methane production from multi-zone completion wells and establishing a rationale for dewatering coalbed methane wells.