Successful Application of Carbon/Oxygen Logging to Coalbed Exploration

Abstract

Summary Two primary objectives of TRW's involvement as integrating contractor for the U.S. DOE's Methane Recovery from Coalbeds Project (MRCP) are (1) to demonstrate that this unconventional methane resource can be characterized and (2) to select target sites with the greatest production potential. It was contemplated that the wireline carbon/oxygen (C/O) logging tool could help the project's activities meet these objectives. A study using the C/O tool was initiated in the Arkoma basin at the Barringer Well 1–11 located in the Kiowa syncline, Pittsburg County, OK. Several nearby wells are producing methane commercially from strata that are associated with these coalbeds. The C/O log has shown that the various coalbeds in the Barringer well can be delineated. C/O ratio measurements have proved a valuable means of determining the presence of coal behind casing. Results from the Barringer well study indicate that this tool can identify and locate coal behind casing for possible recompletion and production of associated coalbed methane. Comparative data based on previous logging programs for the uncased Barringer Well 1–11 and laboratory studies on the coal are presented. Introduction The Arkoma basin contains extensive bituminous coal reserves. Accurate coalbed correlation and coalbed thickness are essential prerequisites to the determination of coal resources and reserves, especially those beds that are particularly gassy. The coals in the basin are generally considered moderately to highly gassy (appx. 200 to greater than 500 cu ft/ton). A range in coalbed methane contents is to be established for each bed and is used in conjunction with the verified coalbed reserves to provide an estimate of the volume of methane in place. Mustang Production Co. of Oklahoma City completed a successful coalbed characterization field test using the C/O tool during Jan. 1980. The cased test well. Barringer 1–11, is located in the Kiowa syncline (west central part of the Arkoma basin), Pittsburg County, OK (Fig. 1). This well penetrates about 18 possible coalbeds of Desmoinesian age (Pennsylvanian) over a 4.635-ft interval (Table 1). Several offset wells are producing methane commercially from strata associated with coalbeds in the Kiowa syncline. The objectives of this field test were to demonstrate that coalbeds can be (1) identified and located behind casing, (2) distinguished from gas-producing zones. and (3) shown to contain gas. Examples of the C/O tool response to coal are presented. Discussion of the field test includes a description of completed MRCP activities in the Arkoma basin, the resulting MRCP well test data, the C/O log field test configuration, and the test description. Comparison of the C/O results were made with openhole log information. Results have shown that the C/O logging tool successfully delineated the various coalbeds in the Barringer well. Application of the C/O log includes:identification of coalbeds behind casing,differentiation of coalbeds from gas zones,location of thin coalbeds on the order of 1 ft thick, anddetermination of coal quality. C/O Tool Response to Coal The C/O log utilizes a high-energy pulsed neutron source that produces 14-MeV neutrons by the deuterium/tritium reaction. Under high-energy neutron irradiation, elements emit gamma rays with specific energy levels. JPT P. 421^