Abnormal Formation Pressure in the Sulaiman Province, Pakistan: An Insight into Factor Affecting Reservoirs in a Compressional Strike-Slip Region

摘要

Various stratigraphic strata encountered in wells drilled in the Sulaiman Depression (SD) of Pakistan are characterized by the development of abnormal formation pressures. An assessment of abnormal pressures is carried out using conventional well logging method and Daines fracture gradient (FG) model, to obtain modified pressure estimates and to get a new insight into the effect of high pressures in the future hydrocarbon exploratory activities in the region. The conventional well data were used to determine the stress environment based on the caliper log (CALI) information. The overburden gradients (OBGrads), pore pressure gradients (PPGs), and fracture gradients (FGs) were derived from studied wells, using resistivity and sonic (DT) logs, followed by Poisson’s ratio curve for various facies types. Findings from the study confirm that wells from the SD show high FGs, whereas the areas in the west (SFB) and northeast (ZA) indicate normal pressure (hydrostatic) environment. The study concludes that tectonic activities and high rates of sedimentation during the Cretaceous (145-65 million years ago) and the Paleogene (65-23 million years ago) have led to the development of overpressure by disequilibrium compaction. This study identified stress regime at deeper level of the Cretaceous and high-pressure intervals at the Paleogene, concluding three distinct rock units of the Cretaceous, Paleogene, and Neogene.