Review of pore-pressure prediction challenges in high-temperature areas

Abstract

Pore-pressure prediction relies heavily on interpretation of seismic and well attributes such as velocity, resistivity, and density which capture porosity changes during shale compaction under vertical loading. Relationships such as Eaton (1975) were developed in the Gulf of Mexico using a relatively simple lithological mix of geologically young sandstones and shale mudrocks at relatively low temperatures. An alternative approach using data from the same region was more deterministic°also with vertical stress (e.g., Hottman and Johnson, 1965; Bowers, 1995). Another approach using mean stress, developed by Harrold et al., (2000) used similar sand and shale sequences at relatively low temperatures from data in southeast Asia basins. All the above approaches can be shown to provide acceptable prediction of pore pressure in shale mudrocks in young, rapidly deposited siliciclastic sequences, such as the Baram Delta, Brunei (Tingay et al., 2009) and along the West African margin (Swarbrick et al., 2011). The results can be calibrated, with careful attention to evidence for lateral drainage or lateral transfer, using data from their associated reservoir. However, in higher-temperature environments (e.g., Malay Basin, Hoesni 2004) these methods fail to deliver predictions, which may be accurate enough for effective well planning and safe drilling. This paper reviews the above methods and how they can be modified for use at elevated temperatures (e.g., above 100°C). However, the review also draws attention to the wide uncertainty inherent in conventional approaches to prediction in some regions, which may require an entirely different approach to pore-pressure prediction prior to drilling.