The role of effective thickness of the Asmari Formation zones on oil production

Abstract

This paper investigates the role of the effective thickness of the Asmari reservoir formation zones on oil production in one of the Iranian carbonate oil fields. Effective thickness is a term that includes the total gross thickness of rocks by lithofacies for a selected wellbore. The lithology of the Asmari Formation in the studied area consists of dolomite, sandstone, lime, dolomitic-lime, sandstone-shale, and shale limestone dolomites. Based on the existing well-logs, the average shale volume, the effective arithmetic means of porosity in the gross intervals, and average water saturation or hydrocarbon-bearing increments of the studied field is calculated from well-logs. The depth interval of 2214 to 2296, in wellbore #A shows 9.6% average shale volume, 27.2% average water saturation, and 20.9% average porosity. The depth interval of 2213 to 2280, in wellbore #B, shows 6% average shale volume, 21.25% average water saturation, and 28.5% average porosity. Based on our petrophysical assessments we divide the Asmari reservoir in the studied field into eight zones. Zone 1 is made of carbonate (calcareous and dolomitic), zones 2 to 5 are mainly sandstone, zones 7 and 8 are calcareous and shale and zone 6 is a mixture of all the above-mentioned rocks. Among these eight zones, there are two main hydrocarbon productive zones. The numerical calculation of in situ oil volume showed that zone two contains 65% of oil volume in this reservoir. This zone with more than 80% of sand has the highest net hydrocarbon column.