Abstract
The complex fracture network formed by volume fracturing of shale gas reservoir is very important to the effect of reservoir reconstruction. The existence of bedding interface will change the propagation path of the hydraulic fracture in the vertical direction and affect the reservoir reconstruction range in the height direction. The three-point bending test is used to test and study the mechanical parameters and fracture propagation path of natural outcrop shale core. On this basis, a two-dimensional numerical model of hydraulic fracture interlayer propagation is established based on the cohesive element. Considering the fluid-solid coupling in the process of hydraulic fracturing, the vertical propagation path of hydraulic fracture under different reservoir properties and construction parameters is simulated. According to the results, the strength of the bedding interface is the weakest, the crack propagation resistance along the bedding interface is the smallest, and the crack propagation path is straight. When the crack does not propagate along the bedding interface, the fracture propagation resistance is large, and the fracture appears as an arc propagation path or deflection. The difference between vertical stress and minimum horizontal stress difference, interlayer stress difference and interface stiffness will have a significant impact on the propagation path of vertical fractures. Large injection rate and high viscosity fluid injection are helpful for vertical fractures to pass through the bedding interface, and low viscosity fracturing fluid is helpful to open the bedding interface. This research work is helpful to better understand the characteristics of bedding shale and the interlayer propagation law of vertical fractures, and to form the stimulation strategy of shale gas reservoir.
Highlights
Horizontal well multi-stage cluster fracturing technology is a necessary means for shale gas reservoir development (Longde et al, 2019)
There is no difference between the vertical stress and the minimum horizontal stress, or when the difference between the vertical stress and the minimum horizontal stress is small, the interface is easy to open, and the vertical fracture will deflect at the interface
The numerical calculation model of vertical crack propagation at the interlayer interface is established by using a cohesive element, and the propagation path of a vertical crack under different conditions is calculated
Summary
Horizontal well multi-stage cluster fracturing technology is a necessary means for shale gas reservoir development (Longde et al, 2019). Based on a cohesive element, a multi-layer hydraulic fracture propagation model considering fluid solid coupling and bedding interface in hydraulic fracturing fluid injection process can be established to simulate and calculate the hydraulic fracture propagation direction under the conditions of different vertical stress, bedding plane angle, and bedding interface tensile strength (Hanyi, 2019; Chao et al, 2020). For the theoretical study of interlayer propagation of vertical fractures, the theoretical derivation is too complex, and the influence of the existence of bedding cementation interface on the height of vertical fractures is not well considered in experiments and numerical simulation. The finite element calculation model of the propagation path of vertical fracture at the bedding interface is established by using a cohesive element, considering the fluid-solid-damage coupling in the process of hydraulic fracturing, The law of vertical crack propagation path under different geological and construction conditions is calculated
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