NUMERICAL MODELLING OF OVERPRESSURE GENERATION IN THE BARROW SUB-BASIN, NORTHWEST AUSTRALIA

Abstract

A numerical basin modelling approach was used to investigate the hydrodynamics and development of overpressures in a Jurassic Prospect in the Greater Gorgon area of the Barrow Sub-basin. Abnormally large fluid pressures have been encountered by numerous exploratory wells in the Carnarvon Basin; however, the mechanisms responsible for overpressuring were uncertain. To better evaluate the risk of encountering overpressures while drilling Jurassic targets in the area, quantitative basin modelling was conducted. Groundwater flow, heat transfer, and hydrocarbon generation were simulated along two geologic cross-sections. Model results for the fluid pressure history of the Jurassic Prospect were constrained by hydrodynamic data from specific wells in the region. A series of modelling experiments was used to determine the relative significance of compaction disequilibrium, tectonic uplift, organic maturation and permeability on overpressure generation. Results indicate that compaction disequilibrium and the permeability of shale layers are the dominant controls on overpressures, while organic maturation does not contribute a significant amount to the pressure anomaly. Quantitative basin modelling applied to pressure prediction provides critical insight needed prior to drilling and well construction.