Unlocking unconventional organic-rich tight carbonate reservoir potential of the Lam Carbonate Member (LCM) in the Shabwah depression, Southeastern Yemen

Organic-rich tight carbonate reservoir potential of the Lam Carbonate Member (LCM) across the Shabwah depression, southeastern Yemen has received limited investigation, particularly regarding its integrated source-rock and reservoir properties. In the current work, a comprehensive assessment combining organic geochemical, mineralogical, and petrophysical analyses of the organic-rich carbonate facies of the LCM encountered in three exploration wells, along with one-dimensional basin modeling analysis, was undertaken to investigate the suitability of the LCM as unconventional oil-tight carbonate reservoir system. Organic-rich carbonates of the LCM exhibit high total organic carbon (TOC) values up to 8.4 wt%, and contain mainly hydrogen-rich Types II and II/III kerogen, implying a strong basis for oil-and gas-source rock charactestics, with mainly oil generating and accumulation potential. The organic geochemical results also reveal that the LCM is interpreted as an oil-saturated source rock with a probability of oil production, as supported by high oil saturation index (OSI) values greater than 30 and up to 145.66 mg HC/g TOC. One-dimensional basin models of three exploration wells also show that the LCM has high oilholding capability, as indicated by transformation ration (TR) values of kerogen from 32% to 50%, and likely resulted due to thermal maturity of peak mature stage of the oil window, with modeled Easy%Ro values of approximately 0.80%–1.00%. The LCM is characterized by high abundance of calcite mineral and favorable silicate and clay mineral, resulting in a high brittleness index of more than 0.80 and up to 0.88, may have contributing to create efficient micro-fracture pores during hydraulic-fracture susceptibility. Moreover, the LCM exhibits limited pore development, with low porosity and very low permeability values, ranging from 0.36% to 7.00%, and from 0.01 to 2.91 mD, respectively, suggesting poor to fair reservoir quality. Consequently, the highlighted results in the current research reveal that the LCM in the Shabwah depression can be considered as an oil-bearing tight carbonate reservoir potential that hydraulic fracturing may be required to facilitate economically viable unconventional hydrocarbon production.