Integrated Study for Hydrocarbon Assessment of Joya Mair Area, Upper Indus Basin, Pakistan Using Seismic Data and Well Logs

Abstract

The Joya Mair oil field is situated in the S-SE fragment of the Potwar Foreland Basin of Pakistan. The basin contains many promising oil producing fields from the Pre-Cambrian to Eocene reservoirs. Overall, the estimated oil reserves in the Potwar Basin are 40 million barrels and a yearly production of about 2.2 million barrels is carried out. Therefore, it acts as one of the most productive oil producing basins in Pakistan. The oil reservoir is structurally present in the anticlinal or dome type structures associated with the E-W Soan syncline, bounded by the Salt range in the south and the Kala Chitta range in the north. The structural arrangement resulted from the compressional tectonic regime between the Indian and Eurasian plates. The region bears a feasible petroleum system, having proper seal and source rocks. The structure of the research area (Joya Mair) is delineated with the help of seven dip lines and two strike lines. The main reservoirs of the area, i.e., the Chorgali and Sakesar limestones of the Eocene age, are interpreted on the seismic lines. The time and depth contour maps are prepared for both reservoir levels that delineate a triangular zone, which acts as suitable traps for petroleum play. The Minwal-X-1 well is drilled on the exact structure, i.e., the anticlinal portion having thrust faults. The well information is utilized to quantify petrophysical information, including shale, porosity, and saturation. A petrophysical study shows a good percentage of effective porosity of 13% in both reservoirs with hydrocarbon saturation up to 75%. The petro-elastic relationship is utilized through model-based seismic inversion, which differentiates the hydrocarbon bearing zones by evaluating the acoustic impedances. The seismic and inverted impedances are incorporated into the porosity estimations using the multi-attributes and probabilistic neural networking (PNN) techniques. The PNN technique is most suitable for dealing with complexities related to lithological heterogeneities. The resultant porosities are verified over the measured porosities and good correlation is observed. The porosity volumetrics delineated a reasonable porosity within the Chorgali reservoir. Hence, the integrated approach, i.e., structural, geological, petrophysical and geophysical, resulted in a reliable potential evaluation of the reservoirs.