Pore pressure study in the berkine basin, south-east Algeria; characterisation of overpressure intervals and implications for hydrocarbon accumulation and exploration

Abstract

In this study, several independent but complementary methods were used to investigate overpressure intervals in the Berkine basin, SE Algeria. The methods used, namely the Eaton sonic method, the drilling D-exponent, and the mud weight, were then correlated and validated with fracture and pore pressure surveys. Pore pressure studies were conducted in 89 wells across the main and the satellite structures of the Berkine basin oilfields. Pore pressure profiles revealed an interval characterised by remarkably high overpressures, situated above the target reservoirs. A north-south stratigraphic and seismic correlation showed that this overpressured interval is hosted in the Upper Triassic to Lower Jurassic succession, which consists mainly of salt, anhydrite, shale, and dolomite thin beds. The overpressure amplitude reached its maximum at the centre of the Berkine basin, exceeding 2.0 equivalent density, and diminishes southwards as the thickness of the host sequence progressively decreases, reaching values of below 1.7 equivalent density.

The overpressured interval, which has been observed throughout the Berkine basin, appears to have contributed to the efficient sealing of underlying reservoir units, including the TAGI and the Paleozoic reservoirs. In light of the observed pore pressure distribution, it would be a worthwhile pursuit to investigate the potential for hydrocarbon exploration in the northern region of the Berkine basin, where higher overpressure is being observed. This result will provide added value to all sedimentary basins having overpressure intervals. Conversely, the presence of the overpressured interval poses a challenge to drilling operations, and the results of this study will facilitate the accurate setting of casing point depths and contribute to improving wellbore stability.