Publications

It has been long known and well documented that most oil and gas accumulations leak hydrocarbons, that this leakage (or microseepage) is predominantly vertical, and that this leakage can be detected and mapped using any of a number of direct and indirect geochemical and non-seismic geophysical methods. It has also been documented that the areal extent of the surface geochemical anomaly can approximate the productive limits of the reservoir(s) at depth. How reliably this can be done depends on the geologic setting, the choice of hydrocarbon detection method, survey design and sample spacing. Proponents of surface geochemical surveys contend that proper use of surface geochemistry -- and proper integration of geochemical results with conventional geologic and seismic data -- leads to better prospect evaluation and risk assessment. How can one quantify the value added by hydrocarbon microseepage data when it is integrated with conventional exploration methods? One way to do so is to compare survey results with results of subsequent drilling. The results of such a comparison are summarized here for more than 2700 U.S. and International wells, all drilled on conventionally developed prospects after completion of geochemical or non-seismic hydrocarbon detection surveys The prospects are located in both frontier basins and mature basins, onshore and offshore, and occur in a wide variety of geologic settings. Targets ranged in depth from 300 meters to more than 4900 meters and covered the full spectrum of trap styles. Prospects were surveyed using a variety of geochemical exploration methods including free soil gas, microbial, iodine, radiometrics, and micromagnetics. Of wells drilled on prospects associated with positive microseepage anomalies 82% were completed as commercial discoveries. In contrast, only 11% of wells drilled on prospects without an associated microseepage anomaly resulted in discoveries. Had drilling decisions included consideration of the hydrocarbon microseepage data, exploration success rates would have more than doubled!