鄂西渝东东岳庙段页岩储层水力裂缝扩展形态与影响因素研究

页岩储层压裂的核心是形成复杂缝网,因此,水力裂缝的起裂、扩展及各工程条件等对压裂缝网的形成都有着重要的影响。对建南气田页岩天然露头展开真三轴物模实验,并对试验结果进行定量分析与表征。分析认为:东岳庙段页岩储层可压性较好,通过水力压裂能形成复杂裂缝系统;东岳庙段页岩储层存在3种裂缝延伸模型,并以模型Ⅲ为最主要的裂缝延伸扩展模型;高角度缝、压裂液粘度和排量是决定压后裂缝形态的主要因素。     

页岩储层可压性评价关键指标体系

从美国的页岩压裂作业经验看,压裂后产能高的气井并非压裂过程复杂、破裂压力高的地层,而是可压裂性好的地层。借鉴美国典型页岩气田的成功压裂经验,从地质评价指标、页岩体积压裂评价指标和工程技术评价指标三方面探索国内页岩可压性评价体系,对页岩气储层的地质特点进行评价,确定总地质储量、地质"甜点"区、成熟度等;获得储层岩石的脆性参数、天然裂缝、地层倾角、地应力等数据,对储层形成体积裂缝的可行性进行评价;探讨压裂增产的方式、射孔方式、压裂液性能等工程技术指标。从中优选影响储层可压性的主导因素,挑选出最能直接反应页岩地质力学可压性的指标,建立一套适合国内复杂地质和工程条件下的页岩气储层可压裂性评价指标体系,为构建页岩可压性评价模型与风险控制方法提供参考指标。     

射孔对致密砂岩气藏水力压裂裂缝起裂与扩展的影响

为降低致密砂岩气藏偏高的地层破裂压力及增加储层改造体积,设计小型水力压裂实验装置,通过鄂尔多斯致密砂岩气藏钻井取心,研究不同射孔数量﹑射孔间距﹑射孔深度及水平应力差条件下水力压裂裂缝起裂与扩展规律.结果表明,射孔可以有效地降低致密砂岩气藏的破裂压力;增加射孔数量可以增加裂缝条数,并且裂缝沿射孔的方向扩展,有利于均匀布缝,提高储层的改造体积;低水平应力差和较小的射孔间距产生的缝间干扰导致裂缝在扩展的过程中发生偏转,缝间干扰随着射孔间距的增加及水平应力差的增大而减弱;射孔深度对于裂缝起裂也有一定的影响,裂缝更容易从射孔较深的区域起裂,为致密砂岩气藏压裂井射孔参数优化提供依据.     

页岩暂堵转向压裂水力裂缝扩展物模试验研究

暂堵转向压裂是提高页岩储层重复压裂缝网改造效果的重要手段，然而该压裂工艺对页岩水力裂缝扩展规律的影响机理尚不明确。因此，基于室内真三轴压裂物模试验，研究页岩暂堵转向压裂裂缝起裂与扩展规律，分析地应力及注入速率等因素对水力裂缝延伸行为的影响，并通过油藏改造面积(SRA)定量表征暂堵转向压裂缝网改造效果。结果表明，暂堵剂可有效封堵初始裂缝，憋压促使水力裂缝发生缝内转向或激活原生天然裂缝系统，提高页岩缝网复杂程度；根据最终水力裂缝形态展，可划分为4种基本类型，包括台阶状缝、激活天然弱面的横切缝、简单多裂缝以及复杂多裂缝网络；不同地应力差异条件下暂堵机理及裂缝延伸规律不同，当水平应力差小于12 MPa时，暂堵剂通过封堵近井筒初始张开的原生层理或天然裂缝，诱导产生与天然裂缝斜交的二次裂缝，当应力差高于15 MPa时，近井筒天然弱面难以激活，暂堵剂通过封堵垂直井筒的初始横切裂缝，诱发形成平行多横切裂缝；增大注液排量可以提高多裂缝形成几率及裂缝沟通面积。     

基于高能CT扫描的煤岩水力压裂裂缝扩展研究

水力压裂是提高煤层气产量的关键技术,但由于煤岩力学性质的特殊性,使其裂缝扩展规律十分复杂,掌握水力压裂裂缝的形成机制对煤层气开发有着重要的意义。在开采沁水盆地南部区域的大型天然煤岩时,将真三轴水力压裂装置和高能工业CT扫描成像技术相结合,研究了天然裂缝、割理发育情况和地应力对水力压裂裂缝起裂和扩展特征的影响。结果表明:天然裂缝和割理在井筒周围的发育程度决定了水力压裂裂缝的起裂位置和破裂压力,裂缝在基质处起裂的破裂压力显著高于在天然裂缝和割理处起裂的破裂压力;在低水平应力差条件下水力压裂裂缝易沿着天然裂缝和割理随机扩展,随着水平应力差增大,地应力对水力压裂裂缝扩展的控制作用增强,合理的水平应力差范围为2～6 MPa,在此条件下易形成一条水力压裂裂缝为主、连通多条天然裂缝为辅的复杂裂缝系统。研究结果可为国内煤储层的水力压裂裂缝预测和压裂设计提供一定的理论参考和设计指导。     

斜井压裂大型真三轴模拟试验研究

通过大型真三轴模拟试验,研究了井斜角,井眼方位角、射孔方式对斜井压裂裂缝起裂压力、起裂位置及裂缝延伸规律的影响,得到了不同参数条件下裂缝起裂和延伸的直观认识.探索通过定向射孔形成一条平整大裂缝的途径,从而降低水力压裂地层的破裂压力,改善裂缝形态,提高压裂成功率,为优化斜井地层射孔方案及水力压裂设计提供依据.实验结果对于提高斜井水力压裂技术水平,改善压裂增产效果具有重要作用.     

利用横波各向异性评价含煤页岩气储层压裂缝高度——以新场地区须家河组五段为例

对比井筒内压裂前后地层横波各向异性的变化,能够直观、有效地评价及检测压裂缝高度。因此,采用该方法对川西坳陷新场地区须家河组五段含煤页岩气储层压裂缝高度进行了评价,结果显示,岩石脆性矿物含量高、岩石弹性模量高、天然裂缝发育程度高的储层段容易被压裂,压裂缝系统产生的地层横波各向异性更强,同时压裂缝也更容易发生垂向延伸,而脆性弱的煤层、碳质页岩层对压裂缝的垂向延伸具有较强的终止作用。建议在类似地质条件下的储层改造方案中充分考虑煤层及碳质页岩层的发育情况,优选射孔及压裂施工深度段,最大程度地改造储层。     

井温资料在南阳油田压裂中的应用

井温资料在南阳油田生产中主要用于判断水力压裂裂缝高度、分析水力裂缝形态和压裂施工效果等.在储层含气时,用于判断套管外是否窜槽、射孔井段是否已正确射孔.运用实例分析了其应用方法.     

裂缝性储层中水力裂缝扩展规律的数值模拟研究

在对裂缝性储层进行水力压裂过程中,天然裂缝的存在会对水力裂缝的扩展产生十分重要的影响。通过建立水力裂缝遭遇天然裂缝的二维平面应变计算模型,采用数值模拟的计算方法,对裂缝性储层中水力裂缝的扩展规律进行研究。结果表明,在水力裂缝扩展过程中,水力裂缝的入射角、远场主应力比以及天然裂缝的胶结强度是影响水力裂缝扩展的主要因素。在低入射角,低远场主应力比的情况下,水力裂缝更易于转入天然裂缝并在缝内延伸;在高入射角,高远场主应力比的情况下,水力裂缝更易于直接穿过天然裂缝;天然裂缝胶结强度越低时,水力裂缝越容易转入天然裂缝并在天然裂缝内延伸。     

射孔对破裂压力及裂缝形态影响数值模拟研究

针对射孔对水力压裂过程中的破裂压力以及裂缝形态的问题,通过建立不同射孔方位和不同远场主应力条件下裂缝扩展模型,将位移不连续方法(DDM)应用于水力压裂过程中的力学分析研究,同时在裂缝扩展准则上运用修正了的G准则-F准则并进行裂缝扩展规律研究.根据不同射孔方位和不同远场主应力条件下裂缝扩展的模拟计算,在地应力大小和方位确定的情况下,破裂压力随着射孔方位的增大而升高,并且随着方位角的增大,裂缝形态会发生转向,而且裂缝壁面粗糙,会增大压裂液摩阻.对于实际的射孔参数优化设计和压裂施工具有参考意义.     

Impact of hydraulic perforation on fracture initiation and propagation in shale rocks

To enhance the oil and gas recovery rate, hydraulic fracturing techniques have been widely adopted for stimulation of low-permeability reservoirs. Pioneering work indicates that hydraulic perforation and layout could significantly affect fracture initiation and propagation in low-permeability reservoir rocks subjected to complex in-situ stresses. This paper reports on a novel numerical method that incorporates fracture mechanics principles and the numerical tools FRANC3D and ANSYS to investigate the three-dimensional initiation and propagation behavior of hydro-fracturing cracks in shale rock. Considering the transverse isotropic property of shale rocks, the mechanical parameters of reservoir rocks attained from laboratory tests were adopted in the simulation. The influence of perforation layouts on the 3D initiation of hydro-fracturing fractures in reservoir rocks under geo-stresses was quantitatively illuminated. The propagation and growth of fractures in three dimensions in different perforating azimuth values were illustrated. The results indicate that: 1) the optimal perforation direction should be parallel to the maximum horizontal principal stress, 2) the crack plane gradually turns toward the direction of the maximum horizontal principal stress when they are not in parallel, 3) compared with the linear and symmetric pattern, the staggered perforation is the optimal one, 4) the proper perforation density is four to six holes per meter, 5) the optimal perforation diameter in this model is 30 mm, and 6) the influence of the perforation depth on the fracture initiation pressure is low.     

Wing crack model subjected to high hydraulic pressure and far field stresses and its numerical simulation

By considering the effect of hydraulic pressure filled in wing crack and the connected part of main crack on the stress intensity factor at wing crack tip, a new wing crack model exerted by hydraulic pressure and far field stresses was proposed. By introducing the equivalent crack length l _eq of wing crack, two terms make up the stress intensity factor K _I at wing crack tip: one is the component K _I⁽¹⁾ for a single isolated straight wing crack of length 2l subjected to hydraulic pressure in wing crack and far field stresses, and the other is the component K _I⁽²⁾ due to the effective shear stress induced by the presence of the equivalent main crack. The FEM model of wing crack propagation subjected to hydraulic pressure and far field stresses was also established according to different side pressure coefficients and hydraulic pressures in crack. The result shows that a good agreement is found between theoretical model of wing crack proposed and finite element method (FEM). In theory, an unstable crack propagation is shown if there is high hydraulic pressure and lateral tension. The wing crack model proposed can provide references for studying on hydraulic fracturing in rock masses.     

水力耦合作用下裂纹扩展演化机理的试验和颗粒流分析

在地应力不断变化的过程中,裂隙水压力的作用机理会变得十分复杂,为阐述裂隙水压力对裂纹扩展规律的影响,基于离散元理论和室内试验,研究了含单裂隙的水泥砂浆试件在单轴压缩和内水压共同作用下的裂纹演化机理。结合岩石颗粒低渗透性的特点,修正了流体与颗粒之间相互作用的计算法则,并改进了流体域参数的计算方法,提出了一种更加适用于脆性岩石的流固耦合模型。研究结果表明：当裂隙倾角为450,内水压为1MPa时,翼裂纹在初始萌生阶段时会沿着最大应力降方向扩展,其扩展方向基本与裂隙平面垂直,并在扩展的过程中使裂纹尖端附近的拉应力消散。试样轴向应力达到峰值后,次生裂纹大量萌生,微裂纹数目随轴向应变增加呈指数关系增长,同时预制裂隙尖端的压应力场得到释放。与传统水压致裂机理不同,水压力并不会沿着萌生的新裂纹一直扩散,在恒定内水压作用下,由于裂隙尖端一直存在部分压应力场,水压力只会沿着翼裂纹扩散,并没有扩散到已经贯通的次生裂纹中。在轴向应力不断变化的情况下,颗粒之间的孔径处于动态变化之中,反过来对水压力的变化规律产生影响,从而形成了3种不同类型的水压变化规律,类型Ⅰ：水压力随轴向应变增加至峰值后迅速下降,但下降幅度不大,之后水压会随轴向应变增加而上升;类型Ⅱ：水压力随轴向应变增加一直增加;类型Ⅲ：水压力随轴向应变增加至峰值后迅速跌落至0MPa,水压力最终消散。     

裂隙岩体损伤局部化分析

裂隙岩体损伤局部化与裂隙扩展状态密切相关,裂隙扩展到一定长度后裂隙的扩展状态发生分叉,一部分裂隙继续扩展,另一部分裂隙停止扩展。裂隙岩体损伤局部化是由裂隙扩展状态分叉产生的,损伤局部化起始位置也取决于裂隙扩展状态。通过对多裂隙扩展状态的分叉分析,得到了含矩形分布裂隙岩体损伤局部化弯折裂纹临界扩展长度及临界应力。根据系数矩阵的特征值与特征向量,确定了裂隙岩体损伤局部化的位置,而且考虑了裂隙之间的相互作用。最后,通过算例分析得到了裂隙岩体损伤局部化临界应力与裂隙列间距、行间距、围压和原生裂隙倾角的关系。     

Fractured rock mass hydraulic fracturing under hydrodynamic and hydrostatic pressure joint action

According to the stress state of the crack surface, crack rock mass can be divided into complex composite tensile-shear fracture and composite compression-shear fracture from the perspective of fracture mechanics. By studying the hydraulic fracturing effect of groundwater on rock fracture, the tangential friction force equation of hydrodynamic pressure to rock fracture is deduced. The hydraulic fracturing of hydrostatic and hydrodynamic pressure to rock fracture is investigated to derive the equation of critical pressure when the hydraulic fracturing effect occurs in the rock fracture. Then, the crack angle that is most prone to hydraulic fracturing is determined. The relationships between crack direction and both lateral pressure coefficient and friction angle of the fracture surface are analyzed. Results show that considering the joint effect of hydrodynamic and hydrostatic pressure, the critical pressure does not vary with the direction of the crack when the surrounding rock stationary lateral pressure coefficient is equal to 1.0. Under composite tensile-shear fracture, the crack parallel to the direction of the main stress is the most prone to hydraulic fracturing. Under compression-shear fracture, the hydrodynamic pressure resulting in the most dangerous crack angle varies at different lateral pressure coefficients; this pressure decreases when the friction angle of the fracture surface increases. By referring to the subway tunnel collapse case, the impact of fractured rock mass hydraulic fracturing generated by hydrostatic and hydrodynamic pressure joint action is calculated and analyzed.     

十屋沙河子组储层裂缝预测

利用古构造应力场二维数值模拟,预测研究区沙河子组岩体的破裂程度,分析古构造应力分布特征,划分裂缝发育级别。预测结果表明,十屋油田沙河子组储层裂缝主要发育在断层位置及其附近地区,储层经历两期构造应力场作用并形成了2期4组裂缝,裂缝主要发育的方向为北东向和南北向。     

Mechanism of action of cracks water on rock landslide in rainfall

In worldwide, the most common triggering factor of rock landslides is extended and intense rainfall. However, different from the soil slope failure caused by softening action of infiltration rainwater, the mechanism of rock landslide in rainfall is not clear. From the view of fracture mechanics, the propagation of cracks on rock slope and the development of sliding surface were researched. Then based on hydraulics formulas and using Sweden arc method, the influence of crack water on stability of rock slope was quantitatively studied. Finally, an example was given to check the theoretical approach. The result shows that the development of sliding surface of rock slope is mainly caused by crack propagation under hydrostatic pressure when the stress intensity factor K _I at crack tip is bigger than the toughness index of rock fractures K _IC, and the failure of slope is the result of hydraulic action of crack water and the softening of materials on sliding surface when the depth of crack water is bigger than a minimum value h _min.     

岩盐水压致裂溶解的数值模拟

在建立岩盐水压致裂溶解过程的固流传质耦合数学模型的基础上，对该过程进行了数值模拟．由模拟结果分析得出，岩盐水压致裂溶解过程裂缝的扩张以及裂缝宽度的变化受水压和溶解双重因素的影响．水压较大时，裂缝扩展速度快，水压对裂缝张开起主导作用；而裂缝内空间增大，会导致缝内水压降低，此时裂缝扩展速度也随着降低，当缝尖压力接近临界破裂压力时，裂缝停止扩张，缝内压力趋于稳定，此时岩盐溶解对裂缝张开起主导作用．