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Obaiyed field lies in northern west Shushan Basin, which considers one of the largest Mesozoic coastal basins in northeast Africa, with high thickness sediment from the Jurassic to Palaeogene. The petrophysical parameters show difficulty in the development of the high gas reserve in the field, which led us to assess the geological systems that could constrain the formation and evolution of the basin concerning the study field. We simulated the tectonic evolution of the basin using a 1D-Airy isostasy backstripping technique with python coding and PetoMode® software. Also, we evaluated the current reservoir petrophysical parameters using TechLog® software. Based on integrating our results, we propose that the Shushan Basin represents a natural case of a Continuous Basin-Centred Gas accumulations model (CBCG) because of four main reasons: a) the vast extension of the Khatatba Formation, b) the coexistence of the source and the reservoir rocks in the Khatatba Formation, c) the low-permeability and gas saturation accumulations of the Lower Safa Member and d) the abnormal pressure of the Lower Safa reservoir because of its compartmentalization, where each compartment has its pressure peak. At a regional scale, this study highlights the effect of tectonics in the evolution of the basins.

We investigated the source rock potential, sequence stratigraphy, and characterized hydrocarbon reservoirs at Otumara field, Niger delta, using integrated 3D seismic, wireline log analysis, and basin modeling. The burial history and thermal maturity were modeled, the reservoirs were delineated, and the petrophysical parameters were also estimated from the wireline logs. The Passey “ΔLog R” method for estimating the preliminary evaluations of the total organic carbon (TOC) from integrating sonic, neutron, and density with resistivity has been used. The results indicate that the primary source rock of hydrocarbons is the Upper Akata Formation, despite a higher TOC percentage in the Agbada Formation. Based on sequence stratigraphy analysis, TA4, TB1, TB2, and TB3 second-order supercycles were obtained in the studied well TD46. The results also revealed that the field has two large net pays with high-quality reservoir facies: a deltaic slope fan at the upper shoreface and a river mouth sandbar at the lower shoreface. Furthermore, the reservoirs were faulted by a series of growing faults that faulted the basin slope. The reservoir facies are characterized by an average of 18% porosity, 1200 mD permeability, 16% volume of shale, and high hydrocarbon saturation of about 85%. Finally, the petroleum system elements have been defined for improved hydrocarbon exploration. In the absence of complete or partial core samples, this case study emphasizes the importance of using wireline logs to estimate organic richness and investigate sequence stratigraphy in clastic sediments.

We used wireline logs, seismic, core data, fluid analysis, and geochemical data to investigate the total petroleum system in the Cretaceous period. Also, we used thin sections and fluid analysis throughout the investigation. Python’s 1-D backstripping technique was used to determine the abrupt changes in subsidence rates and their effect on the reservoir’s quality. The results defined that the potential reservoirs include, from top to bottom, Mauddud, Upper Burgan, Lower Zubair, and Ratawi Limestone. The reservoir facies reflect different environments between the carbonate ramp (Mauddud, Ratawi Limestone, and Minagish reservoirs), delta plain (Zubair reservoir), and margin shelf (Burgan reservoir), and its quality is graded from Mauddud to Ratawi Limestone from top to bottom. The field lies up-dip under Kuwait Bay and represents the continuation of super-giant Greater Burgan Field. It filled with the spilled oil from the down-dip Raudhatain and Sabriyah fields through a structural saddle. Two major tectonic events subsided the deposited sediments by 0.25 mm/year, besides three minor events; however, these events did not affect all Cretaceous reservoirs but only according to their deposition times. Furthermore, according to burial history, thermal maturity, and reservoirs’ fluid geochemical analysis, the Sulaiy (Makhoul) and Minagish formations are likely the primary sources for all Cretaceous reservoirs.

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