Research On Recovery Improvement Proposal Of CO₂ Flooding In Taixing Oilfield

Fu-3 reservoir of Taixing oilfield is the typical low permeability reservoir with complex fault block which has complex internal fracture system and many types of microfacies. Combined with the bad waterflooding effect, it leads to the low recovery ratio of the reservoir. This research started from the re-understanding of the structures and studied on the influences on the remaining oil distribution such as reservoirs, reserves and reservoir performances. Based on the remaining oil distribution rules and the enrichment characteristics, recovery enhancement proposal researches on CO₂ flooding were carried out with the emphases on QK-111 faults of largescale remaining oil reserves by indoor simulation experiment evaluation, reservoir engineering parameters optimization design and site implementation requirements of CO₂ miscible flooding. The establishment researches on CO₂ flooding proposal in Taixing oilfield provide important practical significance to improve the level of these low permeability reservoirs with small faults and guide similar reservoirs to enhance recovery ratio.Based on geological re-understanding, this paper analyzed the master factors of the formation of the remaining oil in Taixing oilfield and carried out the comprehensive study on the influence factors of the structures, reservoirs, reserves and dynamic by the masterstroke of fine reservoir description. According to the remaining oil distribution rules and the enrichment characteristics, this paper optimized the researches on recovery ratio enhancement of CO₂ miscible flooding of QK-111 fault with the emphases on the researches of phase changes of underground crude oil, miscibility pressure and indoor simulation experiment evaluation of oil displacement efficiency. Meanwhile, combined with the remaining oil distribution rules, this paper determined the development principles and methods, optimized the well pattern layer system combination, drew up the injecting parameters and indicator forecast and established the oil recovery enhancement program.Special methods and techniques were used in flooding programming study. For example, in the structure re-understanding study, the combination of the seismic with drilling and logging, as well as the combination of the machine and the interactive interpreter of human brain realized the accurately specify of farewell fault and the scientific combination of fracture system. During the study of flooding programs, CO₂ flooding gas injection swelling experiment, slim tube test and long core test were carried out to prove the feasibility of significantly improving the recovery by CO₂ miscible flooding.The following achievement was obtained by the research:（1） remaining oil distribution is controlled by structure, reservoir and well pattern. Among them, screened included angle, microstructure and microfacies transition zone of farewell fault and the crossrange and the outskirts of the waterline under the control of well pattern are the main potential areas of the remaining oil distribution.（2） Researches on CO₂ flooding proposal of recovery improvement in Taixing oilfield show that crude oil has a strong ability to dissolve CO₂. The higher the gas injection pressure is, the stronger the dissolving capacity is. Thus, it is more conducive to enhancing oil displacement efficiency. The minimum miscibility pressure of CO₂ dissolved in the crude oil of Fu-3 reservoir in Taixing oilfield is 22.11 MPa, which is slightly higher than the current formation pressure 21.00 MPa. Therefore, under the present conditions, we can only conduct CO₂ near miscible flooding. To realize fully miscible flooding, we should raise the reservoir pressure level. CO₂ miscible flooding can significantly enhance the oil recovery. The oil recovery is 18 %-30 % higher than water flooding flowed by near miscible flooding. Immiscible displacement is the worst. The earlier the gas breaks through, the lower the oil recovery is. The breakthrough of CO₂ miscible flooding appears at the end of flooding in general.