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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。
China Earthquake Administration Institute of crustal stress for the first time developed a hydraulic fracturing in situ stress measurement of underground pressure data acquisition system. The system can accurately measure the water pressure in the fracturing section and overcome the influence on the test results due to the flexibility of the hydraulic fracturing test system and the uneven pore pressure in the measuring section, Accuracy of hydraulic fracturing stress test. Field tests show that the downhole pressure acquisition system operating stability, environmental applicability have reached the application requirements. The author of the project team used the system to successfully carry out the in-situ stress test of two sections and compare the data obtained from the downhole and ground acquisition systems of each section separately. The results show that the greater the test depth, the greater the influence of system flexibility and other uncertainties on the test results, and the greater the error of the final calculation result. During the fracturing process, the pressure gradient of the ground-acquired fracturing curve in the step-up phase is basically the same as that of the downhole pressure. In the step-down phase, the pressure gradient of the ground acquisition curve is obviously greater than the pressure gradient in the downhole data acquisition curve. Get each pressure characteristic value, especially the stress value, and the in situ stress value is lower than the accurate value obtained from the downhole data acquisition.