Document Type : Research Paper
1 M.S. Student, Department of Chemistry and Oil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 Professor, Institute of Geophysics, University of Tehran, Iran
This paper investigates the role of the adequate thickness of the Asmari reservoir formation zones on oil production in one of the Iranian carbonate oil fields. Adequate 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 are calculated using well-logs. In wellbore #A, a depth interval of 2214 to 2296 m shows 9.6% average shale volume, 27.2% average water saturation, and 20.9% average porosity. A depth interval of 2213 to 2280 m, 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), and zones 2–5 are mainly sandstone; zones 7 and 8 are calcareous and shale, and zone 6 is a mixture of all the rocks mentioned above. Among these eight zones, there are two primary hydrocarbon productive zones. The numerical calculation of in situ oil volume showed that zone 2 contains 65% of oil volume in this reservoir. With more than 80% sand, this zone has the highest net hydrocarbon column.
- Effective thickness is a term that includes the gross thickness of rocks by lithofacies for a selected wellbore;
- The adequate thickness of the reservoir formation zones plays a vital role in oil production in the carbonate oil field;
- The effective porosity plays an essential role in the production of hydrocarbons and has the most important relationship between the other petrophysical properties of the reservoir;
- Investigation of the adequate thickness of the reservoir formation zones leads to more reliable estimation of oil production;
- The proposed methodology illustrates the advantage of using adequate thickness and effective porosity for increasing oil production.