Pore pressure detection and risk assessment of OBL oil field, offshore Niger delta, Nigeria

Abstract

The Niger Delta is a prolific petroleum sedimentary basin in the Gulf of Guinea and is posed with a major challenge of overpressure development in many of its fields. Integrated study, utilizing 3D seismic data and well logs from four wells, namely; OBL_1, OBL_2, OBL_4 and OBL_5 was carried out in the offshore Niger Delta. The study aims at evaluation of structural influences on pressure development, detection of overpressure zones and consequently examining the risk involved in drilling. Log signatures show decrease in density log values and corresponding increase in sonic log readings in wells OBL_1, OBL_2 and OBL_4. Well OBL_5, reveals increase density log values but decrease sonic log readings. Two regional and few minor faults observed to penetrate the overpressure zones were mapped out and integrated with the surfaces of the tops of the over pressured zones to generate three stratigraphic zones. Aside from under compaction mechanism, the regional faults penetrating the surfaces generated across the overpressure intervals could have influenced pressure development in the wells.