The Potential for Coalbed Gas Resource Development, Western Maracaibo Basin, Venezuela

Roger Tyler¹, Noel Tyler¹, Rafael Tocco², and Vania Savian^2
1 The Advanced Reservoir Characterization Group, Leander, TX
² Servicios Geocinteg, C. A, Venezuela

By applying reservoir characterization practices to Venezuelan coal basins and by integrating knowledge gained in coalbed gas resource and reserve evaluation from the United States, an evaluation of the coalbed gas potential of the western Maracaibo Basin was undertaken. The objective of the evaluation was to define the potential coabed gas producibility and to predict the resources present, by applying concepts and methodologies of coalbed gas resource evaluation from US basins. Tectonic/structural setting, depositional systems and coal distribution, coal rank, gas content, permeability, and hydrodynamics are controls critical to coalbed methane producibility. In the western Maracaibo basin, high gas producibility requires that geologic and hydrologic controls interact synergistically. That potential synergism is apparent in this frontier gas basin, where (1) thick (>60 ft), laterally continuous coals of high thermal maturity (VR: 0.6 to 0.9); (2) numerous anticlinal and faulted structural traps; and (3) basinward flow of ground water through coals of higher rank (subbituminous) and gas content (200 to 400 Scf/ton) and possible migration of thermogenic gases all suggest high potential for coalbed gas accumulation and production. Documented gas shows in the coal beds and in the sandstones bounding the coal packages, further suggest high potential for gas accumulation. Understanding the dynamic interaction among these key geologic and hydrologic controls has been critical for delineation of gas exploration fairways in the Maracaibo Basin where coalbed gas resources are estimated to be significant (10 TCF). Exploitation of these resources should lead to new play trends being established along the western Maracaibo basin and may significantly help the western Venezuelan gas shortage.