Experimental investigation into hydraulic fracture geometry and proppant migration characteristics for southeastern Sichuan deep shale reservoirs

Waterless fracturing technologies for unconventional reservoirs-opportunities for liquid nitrogen

Research progress on evaluation methods and factors influencing shale brittleness: A review

https://link.springer.com/content/pdf/10.1007%2Fs12182-018-0297-z.pdf

Understanding hydraulic fracture propagation behavior in tight sandstone–coal interbedded formations: an experimental investigation

Hydraulic fracture vertical propagation behavior in transversely isotropic layered shale formation with transition zone using XFEM-based CZM method

\n Hydraulic-fracture initiation and propagation in the presence of multiple layers with different mechanical and flow properties are investigated experimentally using a novel fracturing cell. Mixtures of plaster, clay, and hydrostone are used to cast sheet-like and porous test specimens in layers with different configurations and properties. The layered specimens are hydraulically fractured under varying far-field differential stress. Fracture growth is recorded using a high-resolution digital camera. Key frames are subsequently analyzed using digital image correlation (DIC) to reveal microcracks, measure strains, and show other features such as shear-failure events that are difficult to detect with the naked eye.\n The problem of a hydraulic fracture induced in a soft layer bounded by harder layers is considered. We demonstrate numerous laboratory experiments that reveal a clear tendency for induced fractures to avoid harder bounding layers. This is seen as fracture deflection or kinking away from the harder layers, fracture curving between the harder bounding layers, and fracture tilt from the maximum far-field stress direction. These observations appear to be more pronounced as the contrast in Young's modulus and fracture toughness between the layers increases and/or the far-field differential stress decreases. Moreover, when a fracture is induced in a relatively thin layer, the fracture avoids the harder bounding layers by starting and propagating parallel to the bounding interfaces. Fracture propagation parallel to the bounding layers is also observed in relatively wide layers when the far-field stress is isotropic or very low.\n A fracture approaching a dipping, harder layer tends to curve away from the hard layer by kinking toward the high side of the interface. Nonplanar fracture trajectories are observed even in homogeneous materials when the far-field differential stress is relatively low. Furthermore, various other fracture behaviors in layered specimens are demonstrated and discussed, such as fracture offsetting at material interfaces, fracture branching and complex fracture trajectories, and shear failure of weakly bonded interfaces.

Effect of Geological Layer Properties on Hydraulic-Fracture Initiation and Propagation: An Experimental Study

Laboratory experiments are conducted in this study to investigate hydraulic fracture initiation and propagation in porous test specimens in the presence of multiple fluid injection sources and anisotropic far-field stresses. Numerous laboratory observations of fracture growth are documented via clear, high resolution images and digital image correlation analyses. It is clearly shown that injection-induced stresses can appreciably affect hydraulic fracture trajectories and fracturing pressures. We show that induced hydraulic fractures, under our laboratory conditions, are attracted to regions of high pore pressure. Induced fractures tend to propagate towards neighboring high pore pressure injection ports. The recorded breakdown pressure in the fracturing experiments decreases significantly as the number of neighboring injectors increases. When a hydraulic fracture is induced near an injection port that is maintained at a relatively high injection pressure, a secondary fracture can grow at a markedly lower fluid pressure than that of the main fracture. The influence of an adjacent fluid injection source on the hydraulic fracture trajectory can be minimized or suppressed when the applied far-field differential stress is relatively high. Multiple fractures induced from closely spaced injection ports tend to grow towards neighboring ports and perpendicularly to the applied maximum far-field stress. The experimental observations in this paper can serve as benchmark evidence for numerical hydraulic fracturing simulators that are used for modeling field applications.

The Effect of Pore Pressure on Hydraulic Fracture Growth: An Experimental Study

Laboratory visualization of fracture initiation and propagation using compressible and incompressible fracturing fluids

In hydraulic fracturing, breakdown pressure is the peak fluid pressure at which a borehole fractures (breaks down). Several experimental studies showed that the breakdown pressure increases as the borehole pressurization rate is increased (Haimson and Fairhurst 1969; Haimson and Zhao 1991; Ito and Hayashi 1991; Guo et al. 1993a). Theoretical analyses of breakdown dependence on borehole pressurization rate were reported by several authors (Rice and Cleary 1976; Detournay and Cheng 1992; Ito 2008). Different models used in estimating breakdown pressure were comprehensively evaluated and reported by Guo et al. (1993b). Laboratory experiments on dry cement blocks under triaxial stress showed that the breakdown pressure can be reduced by pressurizing the wellbore in a cyclic manner (Falser et al. 2016). Similarly, when a wellbore is maintained at a constant fluid pressure that is lower than breakdown pressure, a hydraulic fracture may be formed after a certain time. This is called static fatigue (Scholz 1972; Cruden 1974; Lu et al. 2015). In this study, we examined three methods of fluid injection in one set of experiments rather than treating them as separate investigations. These three methods include fluid injection at constant rate, cyclic fluid injection, and fluid injection at constant pressure. We performed a series of hydraulic fracturing tests using two-dimensional (2-D) cast specimens to investigate the effect of the borehole pressurization scheme on breakdown pressure. The 2-D nature of our laboratory tests enables one to visualize the fluid leakoff extent of different injection methods around the borehole at specimen breakdown. In addition to investigating the injection methods, the effect of initial fluid saturation was studied through fluid injection in dry and saturated specimens.

Murtadha J. AlTammar

Papers

Effect of Geological Layer Properties on Hydraulic-Fracture Initiation and Propagation: An Experimental Study

The Effect of Pore Pressure on Hydraulic Fracture Growth: An Experimental Study

Laboratory visualization of fracture initiation and propagation using compressible and incompressible fracturing fluids

Effect of Borehole Pressurization Scheme on Breakdown Pressure

Effect of Geological Layer Properties on Hydraulic Fracture Initiation and Propagation: An Experimental Study