Effects of Fracturing Parameters on Fracture Unevenness During Large-Stage Multi-Cluster Fracturing in Horizontal Wells

Abstract

Horizontal wellswith multi-cluster fracturing technology is an effective approach to exploit unconventional hydrocarbon reservoirs. The on-site diagnosis results indicate that multi-cluster fractures always tend to propagate unevenly due to stressinterference, therefore it is very essential to study the effect of fracturing parameters on fracture propagation unevenness. In this paper, the unconventional fracturing model (UFM, Unconventional Fracturing Model) is used to study the effect of multi-cluster fracturing parameters on fracture unevenness in a large stage. This model has been validated with the actual fracturing case on-site in the Longmaxi shale. The investigated parameters include completion parameters (cluster spacing, number of perforations per cluster), pumping parameters (fluid injection intensity and proppant injection intensity). Our simulation results show that firstly reducing fracture spacing will increase stress interference, andhydraulic fractures exhibit a “radial” pattern. Secondly, reducing the perforation number of a single cluster can promote the more uniform propagation of multi-cluster fractures. Thirdly, increasing the fluid injection intensity will increase the fracture length, but will also increase the fracture unevenness. Besides, the injection strength of the proppant has a little effect on the average fracture length and the unevenness of the fracture length. Finally, setting a reasonable cluster spacing and injection fluid strength can obtain a more uniform fracture propagation. Meanwhile reducing the number of perforations per cluster can also reach the goal of propagating evenly. This paper provides a certain reference for the optimization of multi-cluster fracturing parameters in large-stage and multi-cluster wells.

Advances in Hydraulic Fracture Propagation Research in Shale Reservoirs

“…It has been found that the engineering factors affecting fracture propagation in shale reservoirs are mainly the type of fracturing fluid, construction pressure, injection rate, and other factors [153][154][155][156][157][158]. In hydraulic fracturing operations, different fracturing fluids have different viscosities and wettability [158,159], and the viscosity of fracturing fluid is related to the energy consumption during hydraulic fracture propagation; the lower viscosity of fracturing fluid loses less energy during fracturing, the more energy is used for fracture propagation, which is beneficial to hydraulic fracture propagation [10,63,160]; the wettability of fracturing fluid can reflect its disintegration The stronger the wetting of the fracturing fluid, the stronger its ability to disintegrate the rock, which is conducive to the hydraulic fracture communicating more natural fractures and forming a complex network volume [161,162]. The effect of construction parameters on hydraulic fracture propagation was investigated using physical experimental simulations, and it was found that a constant injection pressure could prolong the fracture propagation period, and it was favorable to generate complex, curved hydraulic fractures at a relatively high injection pressure, while it was easy to generate homogeneous, simple fractures at a constant injection rate [163].…”