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Investigating the Effect of Deformation on Hydrocarbon Retention in Shale Plays


Identifying unconventional hydrocarbon retention risks associated with deformation and uplift remain an industry-wide challenge. Hydrocarbon migration out of a source rock may be enhanced by the formation of natural hydraulic fracture networks during deformation. To investigate the effect of deformation and fracture formation on hydrocarbon retention in shale plays, we combine burial, tectonic, and stress histories with fundamental geological observations from several deformed gas plays with similar intrinsic rock properties but different present-day hydrocarbon abundances. Although rapid, significant uplift is often assumed to be associated with greater hydrocarbon loss, observations from our study set indicate that matured source rock formations that experienced rapid, significant uplift may exhibit a lower fracture density and retain more hydrocarbons than more gradually uplifted formations. Additionally, stress history models indicate that for plays with similar fracture window timing and duration, formations deformed at lower confining pressures (i.e., more shallowly buried formations) exhibit a higher fracture density and retain fewer hydrocarbons than formations deformed while at higher confining pressures. The results of these case studies indicate that 1) over a wide range of geologic conditions, uplift rate and magnitude alone are inadequate risking variables; 2) low confining pressure during deformation promotes the formation and preservation of pervasive natural hydraulic fracture networks (hydrocarbon migration pathways); therefore constraining the timing of deformation with respect to uplift provides a risking method to identify plays with low retention; and 3) not all deformed unconventional plays will have low retention or low present-day formation pressures.