Laboratory hydraulic fracturing tests on cubic granite specimens with a side length of 100 mm were performed under true triaxial stress conditions combined with acoustic emission monitoring. Six different injection schemes were applied to investigate the influence of the injection scheme on hydraulic performance and induced seismicity during hydraulic fracturing. Three of these schemes are injection rate controlled: constant rate continuous injection (CCI), stepwise rate continuous injection (SCI), and cyclic progressive injection (CPI); the other three are pressurization rate controlled: stepwise pressurization (SP), stepwise pulse pressurization (SPP) and cyclic pulse pressurization (CPP). The test results show that the SPP scheme achieves the highest increase in injectivity among the six schemes. The CPI scheme generates the lowest induced seismicity while the improvement in injectivity is the least pronounced. The CPP scheme allows increasing injectivity and decreasing induced seismicity, and is suggested as a promising alternative injection scheme for field applications. Thin section microscopic observations of fractured specimens show that intragranular fractures splitting microcline, orthoclase and quartz grains dominate the hydraulic fractures independent of the injection scheme. The SPP scheme creates the largest fracture length, which explains the highest injectivity value among all schemes. Tests with relatively low magnitude of maximum AE amplitude correspond to short fracture length and small portions of intragranular fractures in microcline grains. Quartz grains are more fractured than microcline and orthoclase grains, and quartz chips (natural proppants) are frequently observed adjacent to hydraulic fractures. The laboratory test results show the potential for hydraulic fracture growth control in field applications by advanced fluid injection schemes, i.e. cyclic pulse pressurization of granitic rock mass.

中文翻译：

---

六种流体注入方案下花岗岩的实验室真三轴水力压裂和颗粒尺度裂缝观察

在真三轴应力条件下结合声发射监测，对边长100 mm的立方花岗岩试件进行了室内水力压裂试验。应用六种不同的注入方案来研究注入方案对水力压裂过程中水力性能和诱发地震活动的影响。其中三种方案是注射速率控制的：恒速连续注射（CCI）、逐步速率连续注射（SCI）和循环渐进注射（CPI）；其他三种是增压速率控制：逐步增压（SP）、逐步脉冲增压（SPP）和循环脉冲增压（CPP）。测试结果表明，SPP 方案在六种方案中实现了最高的注入率增加。CPI 方案产生的诱发地震活动最低，而注入能力的改善最不明显。CPP 方案允许增加注入能力并减少诱发地震活动，并被建议作为现场应用的有前途的替代注入方案。断裂试样的薄片显微观察表明，分裂微斜长石、正长石和石英颗粒的粒内裂缝在独立于注入方案的水力裂缝中占主导地位。SPP 方案创造了最大的裂缝长度，这解释了所有方案中最高的注入值。最大 AE 振幅相对较低的测试对应于微斜晶中的短裂缝长度和小部分粒内裂缝。石英颗粒比微斜长石和正长石颗粒更易断裂，和石英碎片（天然支撑剂）经常在水力压裂附近观察到。实验室测试结果表明，通过先进的流体注入方案，即花岗岩岩体的循环脉冲加压，在现场应用中具有控制水力裂缝生长的潜力。