This study was undertaken to experimentally investigate the feasibility of applying CO2 flooding in a carbonate heterogeneous oil reservoir. Actual core samples and fluids were used to carry out the experiments. A complete fluid and rock analyses had been performed. The minimum miscibility pressure (MMP) was determined using empirical correlations and slim tube tests. The swelling and saturation pressure tests were also conducted. The composition of the reservoir rocks were analyzed in detail using SEM, EDS, and ICP-AES. The pay zone under investigation was accurately characterized. Various core flood tests were undertaken to study the effects of CO2 injection pressure, mobile oil saturation, CO2 slug size, and oil viscosity on oil recovery by CO2 flooding.
The results indicated that the application of reservoir Characterization Number (CN) technique provided better and accurate reservoir rock characterization than those obtained by classic methods. The results also showed that immiscible CO2 flooding was capable of mobilizing oil but miscible mode recovered more oil. The CO2 slug size was optimized to be 15 % PVI driven by brine and the increase of mobile oil saturation increased the oil recovery while the increase of oil viscosity reduced the attained oil recovery by the miscible CO2 flooding.
Carbon dioxide flooding has been applied as miscible, near miscible or immiscible mode after matured water flooding as an enhanced oil recovery (EOR) method or as a secondary recovery method. Nowadays, the miscible type of CO2 flooding is the most popular one, in which the CO2 is either continuously injected or intermittently injected with water(1–2). Jarrel et al(3) reported that the CO2 flooding is the second most applied enhanced oil recovery (EOR) method after steam flooding. The applications of CO2 flooding technology also have attained more potential for significant future growth considering the environmental awareness for reducing CO2 emissions from various industrial sources, which would increase availability of CO2 at economic prices.
In 1986, Broome et al(4) in the U. S. used a resource base of 600 reservoirs with a combined 190 billion OOIP, to indicate that the CO2 is the preferred miscible injection solvent and provided additional recovery of 5.5 – 8.5 billion barrels of oil from miscible CO2 floods, from a total of 8 to 15 and up to 32 billion barrels of oil. A major limiting factor for wider utilization of CO2 floods is the availability of CO2 at economic (generally less than $1.50) prices.
An evaluation of the application of the CO2 injection into a Norwegian oil reservoir was presented by Lindeberg and Holt(1). They indicated that this application produced 63 % of initialoil- in-place (IOIP) while water injection recovered 43 % IOIP. The increment in oil recovery by miscible flooding was attributed to improvement in displacement efficiency and reduction in oil viscosity.
The number of CO2 projects has increased in the U. S. and Worldwide(5). Two promising gas injection pilots of a full field non-miscible gas injection schemes implemented in a carbonate reservoir in Abu Dhabi, U. A. E., were reported by Nicolle et al(6).
