Breakdown pressure and fracture surface morphology of hydraulic fracturing in shale with H2O, CO2 and N2
Breakdown pressure and fracture surface morphology of hydraulic fracturing in shale with H2O, CO2 and N2
复制标题
DOI：
10.1007/s40948-016-0022-6
复制
发表时间：
2016-01
影响因子：
5
通讯作者：
Xiang Li;Zi-jun Feng;G. Han;D. Elsworth;C. Marone;D. Saffer;D. Cheon
中科院分区：
文献类型：
--
作者：
Xiang Li;Zi-jun Feng;G. Han;D. Elsworth;C. Marone;D. Saffer;D. Cheon
滑溜水压裂是页岩中最常规的油井增产措施;然而，N2、LPG和CO2都已被用作各种油气藏中的“外来”增产剂。我们探索使用这些气体作为刺激剂对绿色河页岩，以比较由不同气体成分和状态驱动的页岩中的裂缝的形式和行为，并通过破裂压力和由此产生的裂缝网络的形态进行索引。在简单三轴压（10 ~ 25 MPa）和轴向应力（0 ~ 35 MPa）（σ1>σ2=σ3）条件下，对含单轴向盲孔的圆柱试样进行了压裂试验。结果表明：（1）在相同的应力条件下，CO2压裂的破裂压力最大，N2次之，H2O最小，（2）CO2压裂的裂缝形态最复杂，裂缝表面最粗糙，局部伤害最大，H2O次之，N2最小;（3）在注入速率不变的条件下，CO2压力恢复记录在~5 ~ 7 MPa之间表现为冷凝，并通过混相区从气相过渡到液相，而不是像H_2O和N_2那样直接过渡到液相;（4）横向压裂（σ 3轴向）和纵向压裂（σ 3径向）时，各压裂液的最小主应力与破裂压力均呈正相关，CO2的相关系数/斜率最大，H2O最小。我们解释这些结果的机械理解的崩溃，并通过与特定属性的刺激液的相关性。
Slick-water fracturing is the most routine form of well stimulation in shales; howeverN2, LPG andCO2have all been used as “exotic” stimulants in various hydrocarbon reservoirs. We explore the use of these gases as stimulants on Green River shale to compare the form and behavior of fractures in shale driven by different gas compositions and states and indexed by breakdown pressure and the resulting morphology of the fracture networks. Fracturing is completed on cylindrical samples containing a single blind axial borehole under simple triaxial conditions with confining pressure ranging from 10 to 25 MPa and axial stress ranging from 0 to 35 MPa (σ1>σ2=σ3). Results show that: (1) under the same stress conditions,CO2returns the highest breakdown pressure, followed byN2, and withH2Oexhibiting the lowest breakdown pressure; (2)CO2fracturing, compared to other fracturing fluids, creates nominally the most complex fracturing patterns as well as the roughest fracture surface and with the greatest apparent local damage followed byH2Oand thenN2; (3) under conditions of constant injection rate, theCO2pressure build-up record exhibits condensation between ~5 and 7 MPa and transits from gas to liquid through a mixed-phase region rather than directly to liquid as forH2OandN2which do not; (4) there is a positive correlation between minimum principal stress and breakdown pressure for failure both by transverse fracturing (σ3axial) and by longitudinal fracturing (σ3radial) for each fracturing fluid withCO2having the highest correlation coefficient/slope and lowest forH2O. We explain these results in terms of a mechanistic understanding of breakdown, and through correlations with the specific properties of the stimulating fluids.