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<p>Conventional drilling fluids for acidic formation rely on alkaline additives for pH control, making their performance difficult to manage effectively. Using response surface methodology, the proportioning among xanthan gum (XC), potassium humate (KHM), barite (BaSO<sub>4</sub>), sodium chloride (NaCl), silicone film-forming agent (SFA), polyvinyl alcohol (PVA) was optimized. Thus, a novel clay-free, acid-resistant drilling fluid system was developed. It was then evaluated in laboratory tests and field applications. Furthermore, we investigated its mechanism through Zeta potential, particle size, and scanning electron microscopy analyses. The optimized formulation is: 1.402 lb/bbl XC + 3.505 lb/bbl KHM + 24.536 lb/bbl BaSO₄+ 16.824 lb/bbl NaCl + 2.103 lb/bbl SFA + 3.155 lb/bbl PVA. Performance evaluation demonstrated it exhibits excellent wellbore stabilization and inhibition. The API fluid loss was only 5.9&#xa0;ml. Furthermore, its rheological properties remained stable, with a variation of less than 10% upon continuous contamination with 10% dilute sulfuric acid, confirming its stability in highly acidic environments (pH ≥ 2). Application in the WZ uranium mining district further validated its feasibility. The wellbore diameters for the three test wells remained within acceptable ranges of 210–235&#xa0;mm, 198.9–245&#xa0;mm, 218–250&#xa0;mm, respectively. Mechanistic analysis revealed that electrostatic stabilization and a grid effect to entrap and immobilize BaSO<sub>4</sub> and NaCl particles, thereby significantly mitigating the adverse effects of acidic fluid invasion. Simultaneously, PVA forms an encapsulating film that optimizes particle size distribution and enhances particle diversity. This synergy promotes the rapid formation of a dense, low-permeability filter cake, which effectively stabilizes the wellbore. This research provides a viable new solution for drilling operations in acidic formations.</p>

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A clay-free, acid-resistant drilling fluid for wellbore stabilization: development, application, and mechanism

  • 期刊论文

  • 发表日期：

    2026年4月14日

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  • Zhaoyu Tai,
  • Sheng Wang,
  • Yi Qin,
  • Lin Wang,
  • Chengchao Xie

摘要

Conventional drilling fluids for acidic formation rely on alkaline additives for pH control, making their performance difficult to manage effectively. Using response surface methodology, the proportioning among xanthan gum (XC), potassium humate (KHM), barite (BaSO4), sodium chloride (NaCl), silicone film-forming agent (SFA), polyvinyl alcohol (PVA) was optimized. Thus, a novel clay-free, acid-resistant drilling fluid system was developed. It was then evaluated in laboratory tests and field applications. Furthermore, we investigated its mechanism through Zeta potential, particle size, and scanning electron microscopy analyses. The optimized formulation is: 1.402 lb/bbl XC + 3.505 lb/bbl KHM + 24.536 lb/bbl BaSO₄+ 16.824 lb/bbl NaCl + 2.103 lb/bbl SFA + 3.155 lb/bbl PVA. Performance evaluation demonstrated it exhibits excellent wellbore stabilization and inhibition. The API fluid loss was only 5.9 ml. Furthermore, its rheological properties remained stable, with a variation of less than 10% upon continuous contamination with 10% dilute sulfuric acid, confirming its stability in highly acidic environments (pH ≥ 2). Application in the WZ uranium mining district further validated its feasibility. The wellbore diameters for the three test wells remained within acceptable ranges of 210–235 mm, 198.9–245 mm, 218–250 mm, respectively. Mechanistic analysis revealed that electrostatic stabilization and a grid effect to entrap and immobilize BaSO4 and NaCl particles, thereby significantly mitigating the adverse effects of acidic fluid invasion. Simultaneously, PVA forms an encapsulating film that optimizes particle size distribution and enhances particle diversity. This synergy promotes the rapid formation of a dense, low-permeability filter cake, which effectively stabilizes the wellbore. This research provides a viable new solution for drilling operations in acidic formations.