A comparative study of predicted and actual pore pressures in Tripura, India

Abstract

Past well drilled data in Tripura Region confirmed the existence of super pressure regime below the Middle Bhuban formation. In most of the areas, Middle Bhuban is capped by the Tipam, Bokabil and Upper Bhuban formations. But on the top of the Atharamura anticline, it is exposed to the surface offering less sediment thickness and huge risk for drilling. Exposure of Middle Bhuban escalates the possibility of over pressures at shallow depths and may lead to blowouts if the well is not properly planned. Pore pressure prediction is essential to understand the pressure succession in Atharamura Region. In this work pore pressures were predicted from seismic velocities at the synclinal and flank part of the Atharamura anticline and over pressuredzones are identified. When the predicted pore pressures were compared with offset well pore pressures, an excellent match is observed with the offset wells measured pore pressures. The observations which lead to the new level of understanding in selecting the prediction method and regional pore pressure profile were discussed in this paper. Key words: Middle Bhuban, Atharamura anticline, seismic velocities, pore pressure, offset wells.