The Gravity and Magnetic Study of Joya Mair Area, Potwar Sub-Basin, Pakistan

Abstract

  The geophysical study based on gravity, magnetic and borehole data has been carried out in Joya Mair (Potwar Sub basin) area. The objective of the study was to delineate the subsurface structure and assess the remaining recoverable reserves of the Joya Mair Oilfield. The total estimated reserves of Joya Mair Oilfield are 23-25 million barrels (mmbbl), whereas, at present the recoverable reserves are only 10.45 mmbbl (Pakistan Energy Yearbook, 2003). To resolve this problem and delineate the subsurface structure of Joya Mair area, an integrated geophysical study has been done. The geological model based on gravity data constrained with magnetic and borehole data has been computed. This model demonstrates that the Joya Mair thrust (F1) dips 75o SE and penetrates up to the basement, whereas, the Mengan thrust (F2) dips 58o NW and penetrates in the sedimentary wedge up to the depth of 2.6 km. The thickness of sedimentary wedge is 5.8 km in the south and 5.4 km in the north. The estimated net slip computed from this model is 340 meters and 260 meters along F1 and F2, respectively. The model also indicates that the 38 km thick crystalline crust of Indian shield dips at an angle of 2.3o SE. The qualitative and quantitative interpretation of gravity and magnetic data suggestes that F1 and F2 deformed the structural trap in the study area, which shows that the Joya Mair anticline is not a single structure, it is rather faulted into blocks. That is why Joya Mair well did not produce the expected reserves.