Investigation and Comparison of Recovery Factors of Water and Gas Injection into One of the Fractured Reservoirs in South of Iran

The main part of oil produced in Middle East is supplied from carbonate reservoirs, the majority of which are fractured ones. These reservoirs produce higher rates at their early ages which is followed by lower rates   afterwards, leading to low overall recovery values. The purpose of most drillings is to increase production over longer periods. A reservoir simulation study was carried out on a fractured Middle Eastern carbonate field to determine the optimal production strategy. The three possible methods - natural depletion, gas injection and water injection- were then compared. Results indicated that water injection exhibits better recovery values than gas injection and natural depletion. This is expected since rock exhibits intermediate oil-wetting values, meaning that higher recoveries are achieved due to water flooding. The presence of fractured rocks led to early breakthrough and lower recoveries in gas injection method. The different physical mechanisms affecting oil recovery values are discussed and a few suggestion were presented for other fields possessing the same fracture properties and wet-abilities.