Simulation Study of Hydraulic Fracturing on Deviated Well Under Strike-Slip Stress Regime in Tarim Basin, China
Authors: Fu Haifeng , Hou Bing , Zhong Taixian , Zhao Hexiang , Cai Bo , Yang Zhanwei , Wang Liao , Ren Dengfeng , Huang Jinhua 
Published: August 2024

ABSTRACT:
The fracturing of a deviated well has significant advantages in increasing lateral stimulated reservoir area and improving vertical layers coverage. To study the mechanism of fracture initiation, a unique physical simulation method for hydraulic fracturing with deviated well was developed. The large scale of outcrop sample was 762 mm(length)×762 mm(width)×914mm(height). A 3D numerical fracturing model for deviated well based on discrete lattice theory was also optimized. It was demonstrated that: firstly, the fracture initiation was affected by both of the in-situ stress and well orientation. As the increasing of the difference between vertical and minimum horizontal stress, the fracture initiation surface changed from the well axial direction to the inclined direction which transverse to the wellbore. Secondly, in the openhole completion, when the wellbore azimuth was greater than 45° and the wellbore inclination was from 40° to 80°, the fracture initiation pressure was increased rapidly by 35%. Thirdly, in the perforation completion, the orthogonal analysis shows that the high-angle deviated wellbore trajectory (well inclination between 60°-80°, azimuth between 70°-90°) and perforating parameters have the nearly same influence weight on fracture initiation. Lastly, a fracture complexity index chart covering all wellbore inclinations and azimuth angles(0°-90°) has been plotted to reveal the complexity corresponding with the wellbore trajectory. It guided the application of special mixing pumping schedule to decrease the treatment risk under strike-slip stress regime in Tarim Basin.

1. INTRODUCTION
Highly deviated directional wells exhibit significant advantages in enhancing reservoir sweep area and elevating the degree of three-dimensional modification in multilayer systems, widely applied across various Chinese domestic oil and gas fields. For instance, in the Kuqa foreland reservoirs of the Tarim Basin (Weng et al., 2023), characterized by deep burial depths (6000-8000m), substantial thickness (200-300m), elevated reservoir temperatures (150-190°C), and high formation pressures (100-136MPa), the adoption of highly deviated wells coupled with segmented multi-cluster stimulation techniques enables the expansion of lateral exploitation while ensuring vertical effectiveness, achieving similar results to horizontal well stimulation. The ultra-low permeability oil and tight gas reservoirs in the Ordos Basin, with geological features of multiple thin layers and interbedded sand-mudstone (J. Li et al., 2018; Peng et al., 2021; J. Wang et al., 2021), benefit from the highly deviated drilling and segmented modification approach. This method concurrently realizes effective exploitation of both vertically stacked thin layers and lateral reservoirs, integrating the technological advantages of stratified fracturing in vertical wells and segmented stimulation in horizontal wells. On the other hand, due to varying angles between the wellbore and triaxial earth stresses, fracturing operations in highly deviated wells increase the difficulty of fracture initiation compared to vertical and horizontal wells, leading to more complex near-wellbore fracture initiation patterns (Zheng et al., 2019; Zheng, Miska, et al., 2023; Zheng, Ozbayoglu, et al., 2023). Coupled with actual geological characteristics like natural fractures and tectonic stress, issues such as high fracturing pressure and increased risks of sand plugging in field operations become more pronounced. Therefore, accurately recognizing the fracture initiation and propagation patterns and the dominant mechanisms under different conditions in highly deviated wells hold significant research value for effectively guiding the optimization of fracturing process parameters and reducing operational risks.