Present-day in situ Pore Pressure Distribution in the Tertiary and Cretaceous Sediments of Zubair Oil Field, Iraq

摘要

Background and Objective: Supergiant Zubair oilfield is one of the major hydrocarbon producing assets in southern Iraq. This study presents the assessment of pore pressure distribution across the tertiary and cretaceous sedimentary sequences in five producing wells. Materials and Methods: Indirect pore pressure estimation employing compressional sonic slowness responses as well as direct pressure measurements have been combined to establish regional pore pressure profiles. Results: Study reveals hydrostatic pressure regime in tertiary sediments. Late cretaceous Tanuma shales are under-compacted and therefore reveals mild overpressure, while the primary reservoir middle Cretaceous Mishrif limestones are in sub-hydrostatic pore pressure due to production related depletion. Conclusion: This study will be directly beneficial for determining minimum mud weight for drilling, since too high or too low mud weight can result into mud losses and wellbore collapses respectively leading to expensive non-productive time (NPT) in terms of drilling and loss of put on production (POP) time.