Application of a Fully Coupled Fracture-Reservoir-Wellbore Model in Shale Gas Development: Perspectives on Inter-Well Fracture Interference

Abstract

In the unconventional oil and gas domain, shale gas development adheres to the technical concept of "tight well spacing and infill well." Infill wells, along with large-scale hydraulic fracturing, have become effective strategies for increasing shale gas production. Nevertheless, during hydraulic fracturing operations in the horizontal wells, there is often a risk of frac hits due to geological and engineering factors, which has a significant adverse impact on on-site operations, resulting in lower individual well production and posing challenges to the efficient development of shale gas. Managing frac hits is critical for the industry's growth rate in future. Therefore, based on the current state of hydraulic fracturing in the southern Sichuan shale gas, this study aims to clarify the mechanisms of frac hits and the influencing factors, and to propose effective methods for preventing frac hits, thereby improving the performance of gas wells. In this article, we employed a fully coupled reservoir-fracture-wellbore geomechanical simulation method originated from Zheng (2019a), combined with the establishment of shale gas diffusion properties, to establish a frac hits model. A detailed analysis of the mechanisms and influencing factors of frac hits between shale gas wells under different interference patterns were conducted, and the effectiveness of mitigation methods for each pattern was validated. The results indicate that in reservoirs with developed natural fractures, the fractures in stimulated wells tend to propagate easily along these natural fractures, affecting offset wells. To some extent, this impact can be mitigated by avoiding fracturing in the risky stages. Similarly, the depletion of offset wells leads to a rapid decrease in rock pressure around the fracture tip. Due to the influence of pore elastic effects, rocks undergo elastic deformation, resulting in low-stress zones. The fractures in stimulated wells are affected by this phenomenon and tend to propagate towards offset wells, causing frac hits. The application of pre-pressurization in offset wells can lower the occurrence rate of frac hits. The simulation of inter-well interference between offset wells and stimulated wells provides a theoretical foundation for understanding the frac-hit phenomenon in the southern Sichuan shale gas. This method can be used to predict or mitigate the risk and damage associated with frac hits.