AUTHOR=Amjad Muhammad Raiees , Zafar Muhammad , Ahmad Tausif , Hussain Muyyassar , Shakir Urooj 

TITLE=Overpressures Induced by Compaction Disequilibrium Within Structural Compartments of Murree Formation, Eastern Potwar, Pakistan

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2022.903405

DOI=10.3389/feart.2022.903405

ISSN=2296-6463

ABSTRACT=Overpressure conditions in Potwar Basin of Pakistan, pose significant drilling and completion problems. Specifically, in Eastern Potwar, abnormally high pressures are observed within structural compartments of Murree Formation of Neogene age. Compaction disequilibrium and tectonics stresses are considered as two major factors, controlling pore pressures in this foreland basin. Undercompaction of sediments due to high sediment influx, affects the porosity-depth relationship as the rock deviates from normal compaction trend. Demarcation of structural geometries is critical in understanding abnormal pressure conditions within thick molasse deposits of Murree Formation. Eastern Potwar is divided into three zones on the basis of structural geometries, including duplex thrust sheets, salt cored anticlines and triangular zones. Geohistory analysis and pore pressure prediction has been performed for determining the overpressuring mechanism. Log based pressure prediction in different oil fields of Eastern Potwar, depicts anomalous pressure conditions in some of the wells. High sedimentation rate during Miocene times resulted in a low porosity reduction rate due to inability of fluid to escape out of the pores. Eaton’s method was used to predict the pore pressure and these pressure curves are calibrated against measured pressure to validate the results. Pressures predicted in Qazian 1X well, showed very good correlation with measured pressure data. Most of the wells with overpressure intervals exhibited high porosity values showing deviation from normal compaction trend. This pressure prediction revealed that compaction disequilibrium is the primary cause of overpressure conditions within Murree Formation, resulted in response to rapid rate of sedimentation. Deformation mechanism and presence of different structural geometries also contributed in development of abnormal pressures.