Abstract: Applying High-Resolution Surface Geochemistry to Assess Reservoir Compartmentalization and Monitor Hydrocarbon Drainage

Schumacher, Dietmar and Daniel C. Hitzman - Geo-Microbial Technologies, Inc.

New Applications for Field Development: The past decade has seen a renewed interest in geochemical exploration which, when coupled with developments in analytical and interpretive methods, has produced a new body of data and insights in this area. Detailed geochemical and geomicrobiological surveys and research studies have documented that hydrocarbon micro-seepage is a dynamic and predominantly vertical process which responds quickly to changes in reservoir conditions. These important characteristics make possible a new suite of applications for soil gas and microbial surveys including (1) early delineation of field limits, (2) finding by-passed oil and gas, (3) contributions to reservoir characterization, (4) evaluation of infill and step-out well locations, (5) documentation of hydrocarbon drainage over time, and (6) monitoring of waterflood operations.

Because hydrocarbon micro-seepage is nearly vertical, the extent of a soil gas or microbial anomaly at the surface can approximate the productive limits of the reservoir at depth. Furthermore, the detailed pattern of micro-seepage over a field can reflect reservoir heterogeneity and distinguish hydrocarbon-charged compartments from drained or uncharged compartments. Additionally, since hydrocarbon micro-seepage is dynamic, seepage patterns can change rapidly in response to production-induced changes. These applications require close sample spacing and are most effective when results are integrated with subsurface data, especially 3-D seismic data. The need for such integration cannot be overemphasized. Seismic data will remain unsurpassed for imaging trap and reservoir geometry, but, especially onshore, only detailed microbial or soil gas surveys can reliably image hydrocarbon micro-seepage from those same reservoirs.

Time Lapse Monitoring of Reservoir Drainage: There is widespread interest in the industry in the possibility of repeating 3-D seismic surveys at intervals during hydrocarbon production from a field, in order to follow fluid movement through the reservoir and pressure changes within it. This application, known in the industry as 4-D seismic, is most effective with marine seismic data. Results of the detailed microbial (MRC) surveys presented here suggest great potential for such time lapse monitoring of reservoir drainage using repeat high-resolution micro-seepage surveys. Unlike 4-D seismic surveys, micro-seepage surveys are most effective on land and may thus represent a viable alternative to 4-D seismic in some situations. Information gained from such surveys will enable reservoir geologists and engineers to construct more accurate field models, leading to improved development planning and ultimately to increase recovery. We are very excited about the potential of such time lapse studies and have several demonstration projects underway, however, it will be some months before results will be available for public scrutiny and discussion.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil