注入压力对CO_2驱气窜影响规律及裂缝封堵研究

Effects of Injection Pressure on Gas Channeling during CO_2 Flooding and a Study on Sealing of Cracks

为了确定注气压力对CO_2驱油过程中气窜的影响规律,结合矿场实际情况,设计不同注气压力方案,测试不同注气压力下的窜逸时间,得出注气压力与CO_2窜逸速度、采出程度的变化规律。实验结果表明,注入速度、基质渗透率、裂缝大小及宽度是影响注入压力主要因素,合理的注入速度是控制注入压力的关键。注入速度越大,注入压力越大;裂缝越大,注入压力越低;基质渗透率越大,注入压力越小,在此基础上优选淀粉体系合理注入速度为0.2 mL/min。通过岩芯造缝模拟实验可知,气体的波及体积受储层裂缝影响严重,当级差大于1 000时,采出程度小于1%,优选了高强度凝胶体系为:淀粉4%+单体4%+交联剂0.05%+成胶控制剂0.18%,该凝胶体系强度高,成胶时间在8~20 h、性能稳定能够能够有效封堵住裂缝,封堵裂缝后采出程度可达19%,有效扩大了CO_2驱的波及体积。

To determine the impact of injection pressure on gas channeling during CO_2 flooding processes, different injection pressure schemes were set up according to actual oil recovery conditions, through which the breakthrough times with different injection pressures were measured. From this experiment, we obtained the variation of CO_2 breakthrough velocities and recovery rates with injection pressure. The results indicated that injection rate, base substrate permeability, and the size and width of cracks are the most important factors for injection pressure, and the selection of an appropriate injection rate was the key for controlling injection pressure. It was found that the injection pressure increased in proportion with the injection rate, decreased with increases in the size of the cracks, and decreased with increases in base substrate permeability. These results showed that the optimal injection rate for starch systems was 0.2 mL/min. In crack simulation experiments using rock cores, the sweep volume of a gaseous body was significantly affected by cracks in the reservoir, as the recovery rate falls below 1 % for differentials larger than 1 000. The composition of the optimal high-strength gel system was: 4% starch + 4% monomer + 0.05% crosslinking agent + 0.18% antigumming agent. This gel system has high strength, a gelling time between 8 and 20 h, and stable performance; hence, it is capable of sealing cracks effectively. The recovery rate reached 19 % after crack sealing was performed using this gel, thus demonstrating that this gel system effectively increased the sweep volume of CO_2 flooding.