Chapter 5 Light hydrocarbons for petroleum and gas prospecting

Publisher Summary This chapter presents the conceptual and practical application of microseepage detection and interpretation in the evaluation of areas for their subsurface hydrocarbon potential. Surface geochemical prospecting for hydrocarbons includes a myriad of techniques ranging from the direct detection of hydrocarbons escaping from subsurface accumulations and source beds to identifying secondary responses in the soils, rocks, and biota in proximity to such accumulations or source beds. Except in rare instances, surface prospecting cannot reveal the outline of subsurface accumulations, nor indicate the potential commercial worth of a prospect. It allows the explorationist, a means to high-grade prospects, but should never be used as the sole criteria for delineating drilling locations. Surface soil-gas anomalies exist for many understandable reasons, although some do appear rather random. The interpretation of such data is derived from the general ability to extrapolate from macroseepage to microseepage, and the fact that the surface signal detected is directly correlated to gross subsurface hydrocarbon composition. Thus surface soil gas prospecting techniques utilizing hydrocarbons can be a reliable test for indicating the presence of subsurface hydrocarbon source and/or accumulation. Present day exploration for oil and gas requires a coordinated effort based on all useful techniques of geophysics, geology, and geochemistry. The discussion on geochemical-prospecting techniques is useful for exploration geologists and geophysicists who wish to enhance their exploration activities through the use of surface geochemistry.