Multi-stage fracturing with horizontal wells is a pivotal technique for developing the unconventional reservoirs. Owing to complex geological conditions coupled with inherent limitations in existing drilling technologies, a significant proportion of horizontal wellbores deviate from the target reservoir, instead inadvertently penetrating adjacent upper and lower interlayers. These misplaced sections are termed the non-reservoir horizontal wellbore intervals (NRHWI). In this scenario, the cross-layer fracturing with directional perforation (CLFDP) is introduced as an effective stimulation method. Despite its potential, the mechanisms governing fracture initiation and propagation in CLFDP operations remain poorly understood. This study, therefore, develops a three-dimensional (3D) numerical model of CLFDP for Well H in the Changqing Oilfield, China. The model specifically considers a horizontal wellbore positioned within the mudstone interlayer overlying the target sandstone reservoir and incorporates realistic perforation geometry. We systematically investigate fracture morphological characteristics, injection pressure dynamics, and fracture area evolution. The goal is to examine how these parameters are influenced by variations in wellbore location, perforation depth, and perforation spacing. The results demonstrate that a distinctive gourd-shaped fracture yields in the CLFDP case. The horizontal wellbore trajectory should be optimally steered to maximize reservoir contact, leveraging advanced technologies such as rotary steering systems—a critical factor in enhancing stimulation efficiency. In scenarios where the horizontal wellbore deviates from the target reservoir, we recommend employing deep-penetration perforation (with large perforation depth) combined with high-density perforation (reduced perforation spacing) to effectively develop the NRHWI. These outcomes provide essential theoretical underpinnings and technical support to maximally harness the unconventional resources.

Fracture geometry is important when stimulating low-permeability reservoirs for natural gas or oil production. The geological layer (GL) properties and contrasts in in-situ stress are the two most important parameters for determination of the vertical fracture growth extent and containment in layered rocks. However, the method for assessing the cumulative impact on growth in height remains ambiguous. In this research, a 3D model based on the cohesive zone method is used to simulate the evolution of hydraulic fracture (HF) height in layered reservoirs. The model incorporates fluid flow and elastic deformation, considering the friction between the contacting fracture surfaces and the interaction between fracture components. First, an analytical solution that was readily available was used to validate the model. Afterwards, a quantitative analysis was performed on the combined impacts of the layer interface strength, coefficient of interlayer stress difference, and coefficient of vertical stress difference. The results indicate that the observed fracture height geometries can be categorized into three distinct regions within the parametric space: blunted fracture, crossed fracture, and T-shaped fracture. Furthermore, the results explained the formation mechanism of the low fracture height in the deep shale reservoir of the Sichuan Basin, China, as well as the distinction between fracture network patterns in mid-depth and deep shale reservoirs.

Hydraulic fracturing is crucial for extracting shale oil and gas. This technique involves creating fractures in rock formations to enhance reservoir development efficiently. Due to the complexity of shale rock, it is important to conduct multiscale investigations into the fracturing process. Despite extensive research, the technology for deep-underground shale hydraulic fracturing continues to advance as it moves deeper underground. This paper explores the existing technical challenges of shale fracturing, review the current status of physical experiments and numerical simulations, and highlight the importance of multiscale numerical simulation methods. Meanwhile, an integrated approach to optimizing fracturing designs for field cases is introduced. Finally, this paper summarizes the challenges and opportunities in shale hydraulic fracturing, aiming to provide fresh insights into the advancements of hydraulic fracturing technology.