水压致裂原地应力测试井下水压力数据采集系统及其应用研究

The downhole pressure data acquisition system and its application in hydraulic fracturing in-situ stress testing

中国地震局地壳应力研究所首次研发了水压致裂原地应力测量井下压力数据采集系统。该系统的使用可以对井下压裂段的水压力进行较为精确的测量,克服了水压致裂测试系统柔性以及测段孔壁孔隙压力的不均匀性等因素对测试结果的影响,大大提高了水压致裂应力测试的精度。现场测试表明,井下压力采集系统运行的稳定性、环境适用性都达到了应用的要求。笔者课题组运用该系统成功的进行2个测段的原地应力测试,并分别对比分析各测段的井下和地面采集系统得到的数据。结果显示,测试深度越大,测试结果受系统柔性和其他不确定性因素的影响也越大,最终的计算结果误差也越大。压裂过程中,地面采集压裂曲线在升压阶段的压力梯度和井下压力采集曲线基本一致;降压阶段,地面采集曲线的压力梯度要明显大于井下数据采集曲线的压力梯度;地面压力采集计算得到各个压力特征值尤其重张压力值,以及原地应力值比井下数据采集得到的准确值要偏小。

The downhole pressure data acquisition system has first been developed by the Institute of Crustal Dynamics. According to accurately recording the water pressure in a hydraulic fracturing test section,the system can not only eliminates the effects of hydraulic fracturing test system compliance and pore water pressure unevenness in the hole wall,but also greatly improves accuracy of the hydraulic fracturing system. The system has been successfully applied in practice,and its＇ running stability and environmental suitability are satisfied to the requirements of further applications. Recently,two in-situ stress tests were successfully carried out by our work team,then the paper conducted a comparison of the two test results based on the data obtained by downhole and ground data acquisition system respectively. The results show that the test errors become larger with the test depth increasing. Moreover,both of two pressure gradients recorded by ground and downhole data acquisition systems are consistent during the pressure increasing stage,nevertheless,the pressure gradient obtained by ground data acquisition system is significantly greater than the one recorded by downhole system during pressure decreasing stage. The stress characteristics and in-situ stress values,especially reopen pressure,are smaller by ground system than those values obtained by downhole system.