Distribution and Mechanism Forming of Overpressure Shale Gumai on Jambi Subbasin, South Sumatera Basin

Overpressure is one of the geological phenomena associated with significant pressure values on normal hydrostatic gradients. The excess pressure is caused by loading or unloading of sediments. To predict pore pressure values, the Eaton method is used. Supporting data such as wireline logs, formation pressure data, drilling mud weight data, 3D seismic data, and geochemical data, are used to support distribution and control overpressure in the study area. Seismic data processing uses two types of data namely PSDM seismic volume and data speed intervals velocity. Process interval data velocity from seismic is useful in making excess pressure distribution. Seismic PSDM volume is useful for subsurface geological imaging, where in the manufacturing process horizons and structures are determined. Top overpressure in each research well is in the Intra Gumai formation, while the overpressure distribution in the study area is also close to the peak of the Gumai formation. The mechanism of the cause of overpressure in the study area is the unloading mechanism in the form of smectite mineral that has undergone diagenetic processes into illite and hydrocarbon maturity. The overpressure distribution in the research area is associated with a sequence stratigraphy which has low permeability, which is controlled by the intra Gumai formation which has a small permeability to the intra gumai formation, in addition to the excess pressure distribution is also inseparable from the dismantling factor including Diatctite mineral diagenesis to the Ilit Excessive pressure is observed in any research well in Gumai.