An Experimental Investigation of Water-alternating-CO2 Coreflooding in a Carbonate Oil Reservoir in Different Initial Core Conditions

Due to the lack of any significant primary recovery mechanism in one of the Iranian oil reservoirs, enhanced oil recovery methods are considered for early stage application because it has been depleted rapidly about 200 Psig by primary recovery. Therefore, the objective of this study was to experimentally investigate the performance of water alternating gas injection of this field. Core samples were drilled out of reservoirs' rock matrix and were cut approximately 1115 cm long and 3.28 cm in diameter. The live oil used in the experiments has been made by recombination of the stock tank oil with a synthetic gas mixture. All coreflood experiments were conducted using live (recombined) oil at 1,700 psig and a reservoir temperature of 115 degrees F. A total number of four displacement experiments were performed on the cores, including two experiments on secondary wag alternation gas injection and others on tertiary water and gas invaded zones wag alternation gas injections. Prior to each test porosity and permeability of dried core were calculated then 100% water-saturated core was oil flooded to obtain connate water saturation. Therefore, all coreflooding tests started with the samples at irreducible water saturation. These experiments showed that there was significant improvement in the oil recovery for alternating injection of water and CO2. Thus, this method could be suggested as one of the enhanced oil recovery methods for this field with consideration of the economical studies. This laboratory study investigates the potential effectiveness of wag alternation gas injection for recovering hydrocarbons from target reservoir as it would exist in one of these conditions: after naturally depleted as secondary recovery, after waterflooding and gasflooding as tertiary recovery. All of the experiments were conducted at 115 degrees F and 1,700 psig, which represents a low-temperature and low-pressured reservoir with 5,000 ppm brine salinity. The most similar experimental work with the main reservoir condition indicated that approximately 64% oil was recovered after 1 pore volume of wag alternation gas process at 136,000 ppm brine salinity. Tertiary oil recovery efficiency resulting from wag alternation gas injection was significant, leading to final pore volume injected, 50 and 36 for gas and water invaded zones, respectively.