Hydraulic fracturing characteristics and evaluation of fracturing effectiveness under different anisotropic angles and injection rates: An experimental investigation in absence of confining pressure

Sensitivity analysis on the effect of natural fractures and injected fluid on hydraulic fracture propagation in a fractured reservoir

Fe3O4@ZnO nanocomposites (NCs) were synthesized to improve the stability of the wormlike micelle (WLM) network structure of viscoelastic surfactant (VES) fracturing fluid and were characterized by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Then, an NC-enhanced viscoelastic surfactant solution as a fracturing fluid (NC-VES) was prepared, and its properties, including settlement stability, interactions between NCs and WLMs, proppant-transporting performance and gel-breaking properties, were systematically studied. More importantly, the influences of the NC concentration, shear rate, temperature and pH level on the stability of NC-VES were systematically investigated. The experimental results show that the NC-VES with a suitable content of NCs (0.1 wt.%) shows superior stability at 95 °C or at a high shear rate. Meanwhile, the NC-VES has an acceptable wide pH stability range of 6–9. In addition, the NC-VES possesses good sand-carrying performance and gel-breaking properties, while the NCs can be easily separated and recycled by applying a magnetic field. The temperature-resistant, stable and environmentally friendly fracturing fluid opens an opportunity for the future hydraulic fracturing of unconventional reservoirs.

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Experimental Study on the Stability of a Novel Nanocomposite-Enhanced Viscoelastic Surfactant Solution as a Fracturing Fluid under Unconventional Reservoir Stimulation

3D natural fracture model of shale reservoir based on petrophysical characterization

For low permeability coal seam permeability is weak, low degree of gas migration, prone to gas accidents and other issues. In this paper, a numerical model is established to simulate the process of hydraulic fracturing under monotonic loading and cyclic loading, and a method of increasing permeability of coal seam by cyclic loading hydraulic fracturing technology is proposed. Combined with similar experiments, the influence of cyclic load and cyclic load applied parameters on the fracturing effect of coal and rock mass was analyzed by applying a cyclic load with a pulse pump. The effect of cyclic load pressure technology on coal seam drainage was analyzed by application in 20915 gas control roadways of a coal mine in Guizhou. The results show that after fracturing, the fracture extends along the weak plane of the prefabricated fracture, the pore pressure in the fracture is high pressure, and the pore pressure around the fracture decreases step by step. Due to the compression of the crack, the energy is transferred to the two ends of the crack. The pore pressure has an irregular oval distribution, and there is stress concentration. The pressure value reaches 41.48 MPa. After the cyclic load was applied to the model, the pressure reached the maximum value of 27.64 MPa at 3.37 s. Compared with the monotonic load, the pressure value was reduced by 46.27%. Through pressure and ringing analysis, the fatigue damage of specimens can be realized under cyclic loading. In the experiment, the unconstrained initiation pressure was 2.48 MPa, but after the constraint was applied, the initiation pressure increased to 4.58 MPa, and the pressure increase reached about 55%. After multiple loading and unloading, the peak pressure of the specimen can be reduced and the number of cracks can be increased. In the experiment, the gas extraction rate of ordinary drilling was maintained at about 0.019 m3/min, and the gas extraction rate of ordinary fracturing drilling fluctuated at 0.025 m3/min after 21 days of gas extraction. The pumping capacity of 15 Hz and 20 Hz cyclic loading fracturing boreholes tended to be stable after 15 days, which were about 0.041 m3/min and 0.062 m3/min, respectively. Cyclic loading hydraulic fracturing is better than monotonic loading hydraulic fracturing, and the lower the cyclic loading frequency, the better the fracturing effect.

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Lili Han

Papers

Numerical simulation of hydraulic fracturing process in a naturally fractured reservoir based on a discrete fracture network model