低渗气藏CO2驱与埋存的数值模拟

为揭示低渗气藏中注CO_2提高气藏采收率和CO_2埋存(carbon sequestration with enhanced gas recovery,CSEGR)技术的效果,以苏里格气田召10区块为例,开展了注CO_2驱气的长岩心实验,并使用数值模拟的研究手段,分析了该区块采用CSEGR技术的可行性,并重点研究了扩散、吸附、天然裂缝、井型对于CO_2突破时间、气藏采收率及CO_2埋存的影响。模拟结果表明:采用面积为3. 2 km2的平行四边形"二注七采"井网,在气藏衰竭开采至12 MPa后注CO_2,在CO_2突破时能够提高采收率14. 26%,共能实现3. 8×106t的CO_2埋存;在废弃压力3 MPa时注入CO_2采收率仅能增加2. 2%,但CO_2埋存量可提高至1. 44倍;在低渗气藏中扩散和吸附对于CO_2驱的影响不大;随着扩散系数增大,CO_2突破越快,提高采收率效果越差;吸附滞后现象会略微降低提高采收率的效果;天然裂缝的存在会使气窜现象严重,突破时间大大提前,且裂缝渗透率越高,提高采收率效果越差,但依然可以实现CO_2安全稳定埋存;与直井相比,采用水平井注气将使提高采收率效果降低6%～8%,但对埋存有利。

The Numerical Simulation of CO2 Displacement and Storage in Low-Permeability Gas Reservoir

In order to reveal the effect of CSEGR (Carbon Sequestration with Enhanced Gas Recovery) in low-permeability gas reservoirs, a long core displacement experiment with CO2 was carried out based on the actual data of Z10 block in Suzig gas field, and the feasibility of CSEGR in this block was studied by using the numerical simulation. Besides, The effects of diffusion, adsorption, natural fractures and well types on CO2 breakthrough time, gas recovery and CO2 storage were studied by single factor control variate method. The simulation results show: using an area of 3.2km2 parallelogram well pattern with two injectors and seven producers, the CO2 recovery can be improved by 14.26% until CO2 breakthrough through CO2 injection when the gas reservoir is depleted to 12MPa, and the amount of CO2 storage is 3.8 × 106t. However, The CO2 recovery can just be improved by 2.2% through CO2 injection when the gas reservoir is depleted to 3MPa, while the CO2 storage amount can be increased to 1.44 times. The diffusion and adsorption in the low-permeability gas reservoir have little effect on the CO2 flooding. With the increase of the diffusion coefficient, the faster the CO2 breakthrough, and the lower the recovery can reach. Adsorption hysteresis slightly reduce the CSEGR effect. The natural fractures make the gas channeling serious and CO2 breakthrough faster. The higher the permeability of the fractures, the worse the CSEGR effect. But the safety and stability of CO2 storage can still be achieved. Compared with the vertical wells, gas injection by horizontal wells reduce the recovery by 6% -8%, but which is benefit to the CO2 storage.