PP Follow-up While Drilling: Seeking a Pressure Transition Zone in a Back Arc Basin

Abstract

Pressure transition zones are often expected when reservoir and cap rock pressures are thought to be in pressure disequilibrium. This could be either a pressure drainage effect on the cap rock due to drained underlying reservoirs or a pressure increase in the cap rock due to higher pressured underlying reservoirs. However, these transition zones are rarely seen nor verified with available data. As a result, such transition zones are modelled based on concepts from the 3D geological model and connectivity / lack of connectivity with calibration points. The case study aims to show a pre-drill prediction model where the transition zone within the shale dominated cap rock (due to drainage effect from the underlying reservoirs) was critical in order to ensure the optimal placement of the 13-3/8” casing string.