Controls on Petrophysical Properties of the Mauddud Formation, Bahra and Sabriyah Fields, Kuwait

Abstract

AbstractThe petrophysical properties of reservoirs represent several factors such as reservoir quality and volume of oil saturation (PHI, PERM and SW). The relationship between these factors is complementary; migration and trapping of oil is critical to reservoir quality preservation and it is often compromised by closure of the structure, quality of the seal and tectonic activity. In Kuwait, the Mauddud Formation in Bahra Field (BAMA) does not show a sustainable oil production, unlike the Mauddud Formation in Sabriyah Field (SAMA), although both fields are neighboring and separated only by a saddle. Well data reveals a considerable reservoir complexity that distinguishes BAMA from SAMA, which cannot be easily ascribed to facies variability. Geological data (seismic, wireline logs, core and thin sections) indicates four main differences in BAMA compare to SAMA. First, general stratigraphic thinning of carbonate sequences due to its palaeo-proximal position that made it more susceptible to erosion and increased clastic supply and, secondly, a sandier seal rock. Thirdly, there is a degradation of reservoir quality where the average oil saturation and the porosity are 50% and 15% respectively, compared to 90% and 20% In SAMA. Finally, three fault orientations occur in BAMA including a distinct E-W trend, that does not observed in SAMA. Three main possible hypotheses postulated in this study are based on early results.Cementation by meteoric phreatic cements occluded the porosity in BAMA before the arrival of oil. The fresh water penetrations was facilitated by the sandier seal and proximal paleo- environment in BAMA.Onset and partial growth of the trapping structure in SAMA, allowed an earlier oil expulsion to become trapped, retaining secondary porosity, whilst oil bypassed BAMA traps due to later structural growth.The E-W faults in BAMA were responsible for oil migration vertically by breaching the seal rock. The leakage was followed by an influx burial fluids which re-activated cementation in BAMA that was arrested for a short period by the arrival of oil.