Geophysical Insights | Domestic First! Zhejiang Oilfield Successfully Completes Trial of Water-Based Drilling Fluid for Deep Shale Gas Wells
Apr 16,2026
On April 11, the cementing operation for the production casing of the Da'an 9H horizontal well was successfully concluded. This milestone marks the complete success of China's first pilot test of water-based drilling fluid for deep shale gas wells—an initiative spearheaded by the Zhejiang Oilfield Company. The well reached a final drilled depth of nearly 6,100 meters, featuring a horizontal section spanning 1,900 meters. Water-based drilling fluid was utilized throughout the entire wellbore—covering all four drilling sections—for drilling, completion, and logging operations. The fluid facilitated a drilled footage of 2,860 meters during the fourth section, with a drilling cycle of 32.17 days. Key performance indicators met or exceeded experimental expectations, including a wellbore enlargement rate of 5.76% and the safe running of casing within 55 hours.
As a proprietary technology of Zhejiang Oilfield, water-based drilling fluid has already demonstrated significant environmental and economic benefits through its widespread application in shallow-to-medium-depth shale gas drilling operations. However, deep shale gas reservoirs are typically buried at depths exceeding 4,000 meters. Drilling operations in these environments face numerous technical challenges—including high downhole temperatures, unstable formations prone to collapse, and high overall frictional resistance—which impose stringent demands on the drilling fluid's thermal stability, formation inhibition and sealing capabilities, and lubricity. Consequently, developing effective water-based drilling fluid technology for deep shale gas remains a world-class technical challenge. In active alignment with China National Petroleum Corporation's (CNPC) green development strategy—as well as its initiatives regarding the shale oil and gas revolution and the cultivation of cutting-edge shale gas technologies—the Oilfield Company rose to the challenge. Through meticulous planning, it launched a dedicated R&D and pilot program for deep shale gas water-based drilling fluids, proactively driving a "green" transformation in shale gas engineering technologies while simultaneously enhancing efficiency and reducing costs.
The Zhejiang Oilfield Company collaborated with Chuanqing Drilling and China University of Petroleum (Beijing) to establish a specialized project team dedicated to this technical challenge. Following two years of intensive research and experimentation, the team successfully evaluated and optimized a "Potassium Salt Brine-Based Biomimetic Dual-Repellent Water-Based Drilling Fluid System." The comprehensive performance of this system rivals that of oil-based drilling fluids, while offering distinct advantages such as superior environmental friendliness and lower cost. During the field trial at the Da'an 9H well, the project team deployed key technical personnel to remain on-site throughout the entire operation. This measure strengthened technical support in the field, facilitated real-time analysis, and enabled dynamic adjustments to drilling fluid properties, thereby effectively resolving technical challenges such as the prevalence of fractures in the target formation and increased frictional resistance associated with complex well trajectories. Throughout the entire drilling process, the wellbore maintained high stability; cuttings transport and sand removal were effective; and lubrication and drag reduction effects were significant. No engineering accidents or complex downhole situations occurred, thereby fully validating the applicability and reliability of water-based drilling fluid systems in deep-layer shale gas horizontal wells. This success provides comprehensive field data support and technical references for the subsequent large-scale implementation of "water-replacing-oil" strategies.
The successful field trial of water-based drilling fluids for deep-layer shale gas marks a breakthrough, ending the historical reliance on oil-based drilling fluids for deep shale gas operations. It achieves full-depth coverage for water-based drilling fluid technology—extending its application from shallow and medium-deep formations to deep shale gas reservoirs. Furthermore, this achievement fulfills the Group Corporation's strategic mandates regarding the "Shale Gas Revolution" and the establishment of a vanguard in shale gas technology. It signifies a pivotal step forward in the green transformation of shale gas engineering technologies, driving both cost reduction and efficiency enhancement.
Moving forward, the company will systematically consolidate the experiences and data garnered from this trial. We will implement continuous, full-chain optimization—spanning product R&D, system refinement, and field application—to further enhance the key performance indicators of water-based drilling fluid systems, reduce comprehensive operational costs, and accelerate the large-scale adoption of water-based drilling fluids in shale gas development.
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