Gbeibe Fractured Reservoirs Note CO ₂ Miscible Flooding Gas Channeling Technology Research

CO2miscible flooding is currently a very important EOR recovery technology, with its high oil displacement efficiency, low cost advantages, which has attracted national attention. Syria GB reservoir is a fractured reservoir with strong heterogeneity. CO2miscible flooding prone to gas breakthrough, which is not conducive to the full use of low permeability reserves.Based on the laboratory’s previous research, starting from reducing crude oil and CO2interfacial tension, experiment screened for GB during CO2decline displacement efficiency reagent, and optimize the slug size, so that GB reservoir of CO2miscible flooding can be achieved. Develop a weak gel system suitable for GB fractured reservoir CO2miscible flooding anti-gas channeling, and make experimental research on the properties of the weak gel and the feasibility and effect of the anti-gas channeling. Finally, GB actual reservoir cores are used for the long core displacement experiment, evaluation of the CO2drive and weak gel gas channeling technology to improve the recovery of GB reservoir effect. Understanding mainly includes:(1)The formation crude phase experimental results show that:gas ratio is low in crude oil of GB M well, with high density and high viscosity, it is a typical black oil reservoir; The crude oil expandability decreased quickly, viscosity and density increase rapidly, flow ability weakened, resulting in low level of exploitation in the process of depletion type of exploitation.(2) Miscibility pressure experiments show that:in the current reservoir pressure, crude oil in M well of GB reservoir and CO2are unable to achieve the miscible phase, the interfacial tension was screened by reducing mixture GF-2, it can decrease the MMP to9.24MPa, making miscible flooding be realized, and optimized the slug size of GF-20.10%HCPV.(3) The suitable formula of the development of the anti-gas channeling weak gel is:The polymer concentration is1000～2000mg/L, the concentration of cross-linking agent is100～150mg/L, stabilizer concentration is100-200mg/L. retarder concentration is40～80mg/L, oxygen concentration is0～100mg/L, the degree of mineralization is5000mg/L. In GB reservoir conditions, the gelling performance is good, the gelling time is adjustable, and the long term stability is great.(4) The gas channeling weak gel performance evaluation experiments showed that:the gel system has good compatibility with formation water, and it has good salt tolerance, long-term thermal stability and injection with the characteristics of high permeability layer, selective access in heterogeneous ground. Mechanical shearing has a big influence of the gel system, so the field operations should minimize the shear degree.(5) Weak gel anti-channeling in the single rock core experiment shows that:injection of weak gel slug size in CO2flooding experiments is late0.16HCPV than which only in CO2gas breakthrough, the ultimate recovery increased by11.41%; it indicates that the weak gel can make efficient in anti-gas channeling and improve oil displancement efficiency.(6) Weak gel anti-channeling parallel core experiments show that:when injecting CO2 miscible flooding to homogeneous parallel cores, most of the CO2from the high rock flow, low permeability core’s recovery rate is very low. After injected anti-gas channeling weak gel, low permeability core of the gas flow rate is increased by51.14%, recovery degree increase57.94%, the total oil displacement efficiency is increased by32.08%, it shows that the gel system in heterogeneous reservoir CO2flooding process preventing gas channeling and enhancing the oil recovery ratio.(7) GB reservoir long core displacement test shows:the ultimate oil displacement efficiency of GB reservoir water drive, near miscible CO2flooding, CO2miscible flooding and CO2miscible flooding-weak gel anti-gas channeling test were62.19%,72.45%,78.62%and87.22%; in CO2flooding test, the gas breakthrough time from early to late were near miscible CO2flooding, CO2miscible flooding and CO2miscible flooding-weak gel anti-gas channeling test. It indicates that, in4kinds of displacements of the GB reservoir, CO2miscible flooding enhance the maximum oil recovery and the minimum water drive, CO2miscible flooding and weak gel technology make an anti-gas channeling effect, and enhance the oil recovery.