An Integrated Reservoir Characterization Study of The Cretaceous Lower Goru Tight Sands, Middle Indus Basin, Pakistan

Abstract

Due to the depletion of conventional reserves, understanding the unconventional resource potential of tight sands is significantly important. The successful exploitation of this resource in the Middle Indus Basin, Pakistan, has the potential to alleviate the energy crises. Characterizing the tight reservoir potential of the Lower Goru Formation in the Middle Indus Basin is challenging due to its heterogeneous nature. This study employs an integrated approach, utilizing well and seismic data, to characterize the tight sands in the Lower Goru Formation. Lab techniques, including thin-section petrography, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and porosity and permeability measurements, were employed to understand the depositional and diagenetic processes. Permeability prediction, log-based sequence stratigraphy, heterogeneity assessment, diagenetic facies identification, and porosity and saturation evaluation in these siliciclastic reservoirs were conducted through integrated core-log petrophysical analysis. Elastic properties were computed from well logs using a rock physics approach. Porosity and permeability distribution across the reservoir were assessed using Sequential Gaussian Simulation and Gaussian Random Function Simulation algorithms. Seismic volumes were inverted into an acoustic impedance volume using Simultaneous Seismic Inversion. Authigenic chlorite and quartz cementation primarily control reservoir quality. Well-developed chlorite coatings preserved porosity and inhibited quartz cementation. In the Sawan gas field, sand-dominated delta plain/ marginal marine embayment and the middle shoreface facies exhibit tight reservoir characteristics. Tide-influenced channels, mouth bar sands, delta fringe deposits, offshore to shoreface and tide-influenced delta front facies demonstrate tight reservoir characteristics in the Kadanwari gas field. In the Miano gas field, bioturbated storm sand facies show characteristics of tight reservoirs. Core-log integration suggests that the reservoirs are deposited in the highstand system tract, and cross-plotting response of different logs leads to the identification of diagenetic facies. The Flow Zone Indicator method provides more accurate prediction of permeability in these heterogenous reservoirs. The challenges associated with the tight reservoir petrophysics can be minimized through integration of log-core, lab-based and cross-validation using rock physics approach. Rock physics indicates that the acoutic impedance of the gas sands is below 11000 kPa.s/m. The sweet spots are identified in regions where the acoustic impedance is less than 11,000 kPa.s/m. Integrated petrophysics and rock physics diagnostics indicated the tight gas sand hydrocarbon potential in the Sawan and Miano gas fields. The G sand and B sand intervals of the Kadanwari gas field, along with the B hot sands of the Miano gas field, exhibit excellent potential as tight gas reservoirs. The integration of acoustic impedance with petrophysics and rock physics identifies the C sand of the Sawan gas field as a potential sweet spot for tight gas. Similarly, in the Kadanwari gas field, the G sand and B sand intervals exhibit tight gas sweet spots. The integrated results are highly encouraging for the Miano C and B hot sands as candidates for unconventional tight gas sands. Based on the integrated reservoir characterization approach, it is concluded that the Lower Goru Formation within the Middle Indus Basin holds significant potential for tight sands exploration and development.