Implementation of HPHT RSS for Performance Improvement in Deep Shale Gas Drilling

Abstract

Sichuan shale gas development will move to reservoirs deeper than 3,500m TVD in the future after a production milestone breakthrough of 10 billion m3 per year from Southern Sichuan basin was achieved. 80% of Sichuan shale gas total resources will come from deep reserves compared to reservoirs at a shallower depth. Improvements in drilling efficiency are the key success factor of deep shale gas development to enhance production and cost control with the increasing activity. Due to complex engineering and geological conditions, drilling deep shale gas horizontal wells in the Southern Sichuan basin is more challenging than traditional shallower wells. The High Pressure and High Temperature (HPHT) harsh drilling environment has caused the frequent failure of the standard Rotary Steerable System (RSS), Measurement While Drilling (MWD), and Logging While Drilling (LWD) tools during recent drilling operations. The surface cooling system, combined with thermal mitigation practices, positively impacted the increasing trend of bottom hole circulating temperature (BHCT) and extended equipment life in short horizontal sections. However, thermal mitigation reduced in effectiveness with the increase in the length of the horizontal section as frictional heating increased. BHCT reached above 150degC while drilling and exceeded the operating limits of standard tools. The challenge of managing the circulating temperatures resulted in approximately 50% of the total runs in 2020 being tripped before the run objectives were met, creating non-production time (NPT) and significantly decreasing drilling efficiency. To overcome this challenge and reduce NPT, two options were evaluated. A high-temperature Motor bottom hole assembly (BHA) brought risks of poor well trajectory control, resulting in well placement issues during geosteering, and lower potential reservoir exposure. For the first time in China Shale gas, an HPHT RSS with near-bit gamma-ray imaging was selected to maximize drilling efficiency and reservoir exposure. In addition to the tool selection, an HT optimization process was created that included horizontal well BHCT modeling and prediction and deep shale gas RSS drilling best practices. The near-bit gamma imaging quality was enhanced to improve steering. These changes delivered record runs in deep shale gas long horizontal wells and significantly decreased NPT. Reducing the reliance on surface cooling systems also increased overall operating efficiency. This paper reviews the choice of equipment, implementation of HPHT RSS, and development of HT optimization process that improved the drilling efficiency, reduced well time and enhanced long horizontal well placement in this complex drilling environment.

Application, Prospect, and Challenge of Small-Spacing Stereo-Staggered Well Pattern Deployment Technology in the Shale Oil Reservoir

“…In the field exploitation practice of shale oil, the area with high abundance of movable reserves in the sweet spot should be preferred for well location deployment. • Engineering factors: The application of rotary steering technology (Janwadkar et al, 2009;Yan et al, 2021;Al Amri et al, 2021) and element logging technology (Zhu et al, 2018;Zhang et al, 2021) has greatly improved the drilling rate of horizontal wells. Research shows that the foundation of high shale oil production is to make the horizontal section as much as possible in the reservoir, especially in the area with high reserves.…”

Cement Sheath Integrity in Anisotropic Shale Formations: A Numerical Investigation

“…High horizontal stress anisotropy is one of the main characteristics of deep shales. For example, in the southern Sichuan Basin in China, the maximum horizontal stress difference can reach up to 25 MPa [47][48][49][50]. In this section, the behaviors of the cement sheath under different horizontal stress anisotropies (6 MPa, 15 MPa, 20 MPa, and 25 MPa) are analyzed.…”