Overpressure Generation Mechanism in One of Hydrocarbon Fields in Southern Iran

Pore pressure is defined as the pressure of the fluid inside the pore space of the formation, also known as the formation pressure. When the pore pressure is higher than hydrostatic pressure, it refers to as overpressure. Overpressure can make many problems such as kicks, blowouts, wellbore instability, hole washouts and loss of drilling mud circulation. Overpressure is generated due to different mechanisms; such as, compaction disequilibrium, oil to gas generation, buoyancy effect and lateral transfer. Each mechanism effects on exceed pressure in a significant way. So far, several methods have been proposed in pore pressure prediction using well logs and seismic data. Each method relies on a consideration that over pressure is resulting from a specific mechanism as the main factor, and it is also provided an empirical formula for estimation of pore pressure. Hence, geological studies to understand the overpressure generation mechanism and also choose the appropriated pore pressure estimation method are very important. The main objective of this study is to determine the mechanism of high pressure using well log information and provides the best method of estimating the pore pressure in one of hydrocarbon fields in southern Iran. To obtain this goal, the overpressure mechanism generation is studied from sonic log, density log, pore pressure and vertical effective stress information. The results suggest more disequilibrium compaction as the main mechanism and less unloading mechanism behind the overpressure. So, the Eaton and Bowers methods are used to estimation pore pressure and the results show agreement with the pore pressure prediction from formation pressure test.