In this study, pore pressure prediction for a HPHT exploration well was conducted using both convention 1D modeling method and 3D basin modeling approach. Due to the considerable challenges encountered in three nearby fields (narrow mud weight windows, over pressure up to 17.0-17.8 ppg, and temperature as high as 185 °C at projected well TD), 3D basin modeling was considered as an alternative approach to help reduce the uncertainty due to lack of constraining data for conventional 1D modeling.
Both Eaton and Bowers methods were used to generate 1D models of the pore pressure profile from seismic interval velocity. Calibration of the models was based on offset wells of the three nearby fields. On the other hand, 3D basin modeling approach was used to model all three fields together. Detailed lithology was defined for each layer of the basin. By carefully calibrating the relationship of porosity-effective stress, porosity-permeability, and varying sealing capacities of the faults, a good match was obtained between the 3D basin pore pressure distribution and pressure data measurements from offset wells of all three nearby fields. After the calibration process, pore pressure profile of the HPHT exploration well was extracted along the proposed drilling well path.
Modeling a basin consists of reconstructing the deposition history of the entire sedimentary sequences from geological, geophysical, and geochemical data. It allows establishment of paleo water depths and heat flows in burial sediments to understand the hydrocarbon generation, migration, and accumulation processes during the geological history of a basin. The accurate definition for porosity-effective stress and porosity-permeability relationship of layers of source rock, reservoir, and seal will generate reliable pressure regimes in the basin. Extraction of 1D pore pressure profiles showed an excellent match with measured pressure in offset wells.
In addition to providing pore pressure prediction to optimize drilling plans, 3D basin modeling could deliver rock properties data for further wellbore stability studies in exploration areas. This is valuable for HPHT offshore drilling to help reduce the possibility and severity of drilling issues such as kicks, losses, and wellbore collapse.