Pulsed Fracture Research Articles

3D pulsed fracture initiation and propagation around wellbore: A numerical study

Subjected to the extremely high pressurization rate, the pulsed fracture (PF) can branch to form a complex fracture network around the wellbore, which is the most desired in the reservoir stimulation. To study the PF behaviors further, the 3D numerical simulation is conducted. The rock formation is modeled by the augmented virtual internal bond method, which needs no separate fracture criterion in fracture simulation since the micro fracture mechanism has been embedded into the macro constitutive relation via micro bond potential. The simulation results demonstrate that the 3D PF always presents an ear-like profile. Some branched fractures advance towards the minor in-situ stress direction. The higher the pressurization rate is, the more complex the generated fracture network is. The longer isolation section makes the fracturing process easier. The PF speed is governed by the rock modulus. Besides these qualitative observations, some quantitative conclusions have been drawn. The findings of this work can deepen understanding on the PF and provide valuable references for PF operation in a reservoir.

Numerical simulation of pulsed fracture in reservoir by using discretized virtual internal bond

Driven by the pulse pressure, fractures can branch and form a complex network, which is mostly desired in the reservoir stimulation. Thus, the pulsed fracture(PF) should be an inspiring potential technique to improve the reservoir. To explore the regulations of the pulsed fracturing process in field size, the PF is simulated by using the discretized virtual internal bond method. The normal triangular and the in-situ measured pulse are respectively taken as the pressure input in the numerical simulation. It is found that in the high in-situ stress contrast condition, the simple fracture symmetrically initiates on the wellbore wall and then propagates along the major in-situ stress direction. After the fracture advances a certain distance from the wellbore, it suddenly branches in the radial pattern, which forms a complex network. The distance of the fracture network to the wellbore is determined by the difference of the two principal in-situ stresses. The smaller the stress difference is, the closer the fracture network is to the wellbore. On the post-peak stage of pulse, the fracture network still grows self-similarly, but the growing velocity decreases with increasing the unloading rate. When the loading time is fixed, the peak pressure has significant impact on the fracture network profile. The higher peak pressure can generate a larger and more complex fracture network. It is observed that many branched fractures oblique stretch towards the minor in-situ stress direction, which is very helpful for the PF connect to the reservoir in that direction. In addition, the fracture network is generated at a certain distance to the wellbore in the larger in-situ stress difference cases, which is in favor of the wellbore stability. Besides these qualitative regulations, some quantitative conclusions are drawn in this paper. These provide valuable references for the assessment of the PF stimulation in reservoir.