Peng Zheng

Bio: Peng Zheng is an academic researcher from Xi'an Shiyou University. The author has contributed to research in topics: Hydraulic fracturing & Geotechnical engineering. The author has an hindex of 3, co-authored 3 publications receiving 88 citations.

Parallel panel crack simulation device under leak-off condition of fracturing fluid

Abstract: A parallel panel crack simulation device under the leak-off condition of a fracturing fluid comprises a crack formed by two parallel organic glass panels, a fracturing fluid inlet and a fracturing fluid outlet, wherein compact sponge is adopted at the upper ends and the lower ends of the two parallel organic glass panels to serve as an interlayer, rubber pads are adopted on the left side and the right side to serve as interlayers to form simulation crack sections, the compact sponge is adopted at the upper end and the lower end to serve as the interlayer, only a liquid phase is allowed to pass, and a solid phase isn't allowed to pass; the fracturing fluid inlet and the fracturing fluid outlet are designed at the left end and the right end of the simulation crack section, are located at the centers of the parallel panels and are rectangular; and devices for collecting filtrate are arranged at the upper end and the lower end of a leak-off liquid collecting part of the fracturing fluid, and valves are mounted at upper and lower outlets and can be used for adjusting the leak-off speed and the leak-off amount. The device can simulate various true conditions such as sand carrying condition, sand paving condition, migration rules, leak-off and the like of the fracturing fluid entering the crack, and a basis is provided for preference of fracturing displacement, speed and sand ratio and the formula during fracturing design.

Simulation of Fracture Morphology during Sequential Fracturing

Abstract: During hydraulic fracturing, the aperture of hydraulic fractures will shrink by the in-situ stress, but will not fully close because of the existence of proppant inside the fracture. In previous studies, few people noticed the existence of proppant, which has resulted in the inaccuracy of simulation results. In this study, based on the boundary element method, a numerical simulation model for sequential fracturing was established, which respectively considered the influence of proppant in staged fracturing and zipper fracturing. In addition, the influence mechanism of proppant on fracture morphology is then revealed. Simulation results show that the residual aperture of the previous hydraulic fracture, which was produced by proppant, may increase with the increase of proppant stiffness and fracture spacing and may also be shrunk by the dynamic propagation of subsequent hydraulic fracture. However, the residual aperture will rebound after hydraulic fracturing construction is finished. The shrinkage and rebound values of residual aperture of hydraulic fracture are usually less than 1 mm. In addition, at the same time, the residual aperture of previous hydraulic fracture may also influence the propagation of subsequent hydraulic fracture. These influences are represented by the bend of fractures in multistage fracturing and the intersection in zipper fracturing. With the increase of well spacing, the influence degree of residual aperture on subsequent fracture propagation is reduced. The previous hydraulic fracture cannot have a significant effect on the deflection of subsequent hydraulic fracture when fracture spacing is between 10 and 30 m. The above research has important guiding significance for controlling fracture morphology in hydraulic fracturing.

Factors Controlling the Hydraulic Fracture Trajectory in Unconventional Reservoirs

Abstract: The morphology of hydraulic fracture is affected by many factors. In previous studies, due to the heterogeneity of rock samples and the limitations of sample size, influence degree of various factors on fracture deflection angle has not been well distinguished in laboratory experiments. Based on the boundary element method, we established a mathematical model to study the factors controlling the morphology of hydraulic fracture. Simulation results show that with increasing injection pressure, the radius of the fracture curvature increases. When the difference between the injection pressure and the maximum principal stress is 5 times the ground stress difference, the influence of in situ stress on hydraulic fracture deflection can be ignored. Hydraulic fracture deflection angle was relatively larger when considering the viscosity of the fracturing fluid. When stress difference is too small or the injection pressure is too big, the deflection angle of fracture is easy to fluctuate during initial propagation. Too large Young’s modulus and too small Poisson’s ratio will inhibit the fracture deflection and cause a narrower width of fracture. The effect of Poisson’s ratio on fracture aperture is less than 1 mm. When perforation angle is perpendicular to maximum horizontal principal stress, the fracture width first increases rapidly and then gradually decreases from heel to tip. The influence degree of each factor on fracture deflection is ranked: stress difference of in-situ stress is the biggest, followed by injection pressure and perforation angle. This study is of great significance for the control of hydraulic fracture morphology and the further improvement of fracturing effect.