Estimation of pore pressure considering hydrocarbon generation pressurization using Bayesian inversion

Abstract

Under-compaction and hydrocarbon generation are the main factors affecting pore pressure. The current seismic pore pressure prediction method is to obtain the overpressure trend by estimating the normal compaction trend (NCT) to predict the physical parameters during normal compaction and comparing the measured parameters. However, selecting a single parameter to indicate overpressure may cause insufficient consideration of factors such as hydrocarbon generation. Since hydrocarbon generation requires specific temperature and other conditions, we roughly divide the pore pressure into two parts: under-compaction in the early stage and hydrocarbon generation after reaching the hydrocarbon generation threshold. We propose a petrophysical model for estimating the normal compaction trend before hydrocarbon generation, modify the bulk modulus of the model, and use the bulk modulus method to calculate the pressure generated by under-compaction; the pressure is added to obtain the final pore pressure. In the shale gas work area in the Sichuan Basin, the prediction results are more in line with the actual situation, and the petrophysical analysis shows that the ratio of free hydrocarbon content and kerogen to water is the influencing factor indicating pore pressure. The practicality of the pore pressure prediction formula considering hydrocarbon generation in oil and gas sweet spots is illustrated through an example in the research area.