Shale–oil potential in Shabwah depression, southeast Yemen: A geochemical and basin modeling perspective

Abstract

The Lam and Meem organic-rich shale facies of the Upper Jurassic Madbi Formation in the Shabwah Depression are subjected to multi-scale geochemical, petrographical and mineralogical investigation, alongside bulk kinetics and basin modeling analyses for understanding the unconventional oil shale reservoir potential. The studied shales exhibit significant organic matter, with total organic carbon (TOC) between 1 wt % and 12.3 wt %. The Lam and Meem shale facies are also charactersied by hydrogen rich kerogen types II and II/III. The dominance of such hydrogen-rich kerogen was confirmed from the Py-GC and FTIR structures of the kerogen fraction, exhibiting the possibility of producing commercial amounts of paraffinic–naphthenic–aromatic oils with low wax content. The studied shale facies is currently thermally mature, with the Meem shale facies entered the peak-stage of the oil window, based on measured vitrinite reflectance (VRo) values and high oil saturation index (OSI) values. This claim agrees with the bulk kinetic results, which suggest that the commercial amounts of oil can generate by kerogen conversion of up to 50 % during the peak stage of oil window at geological temperature values between 132 °C and 155 °C, consistent with computed vitrinite reflectance values of 0.77–1.07 %Ro. 1-D basin modeling suggests the Meem shale source rock system is more than the Lam shale source rock, entering the main oil generation during the lower Cretaceous to Late Oligocene time, resulting in commercial quantities of oil, having transformation ratio (TR) i.e. up to 55 %. This high maximum oil generation, alongside high brittleness index leads to create non-fabric fracture pores within the Meem shale facies, which may have increased by elevated pressure during the deep burial depths. Therefore, the Meem shale facies is considered for unconventional shale oil reservoir with recommendation of hydraulic fracturing techniques for unconventional production.