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<p>Offshore deep-water drilling demands environmentally compliant drilling muds that can maintain stable rheological and filtration performance under both permafrost seabed and high-pressure high-temperature (HPHT) conditions. Conventional ester-based muds often suffer from poor low-temperature flowability or inadequate thermal stability, limiting their applicability in such challenging environments. This study investigates 2-ethyl-1-hexyl butyrate (EHB), a low-molecular-weight branched ester, as a novel synthetic base oil for offshore drilling applications and characterizes its physicochemical and biodegradation properties to assess environmental compatibility and operational suitability. Drilling muds were formulated using varying mud weights, oil/water ratios, and emulsifier systems, including a natural phospholipid-based emulsifier (soya lecithin), and were evaluated for rheological performance at 3&#xa0;°C and after thermal aging at 150&#xa0;°C for 16&#xa0;h. HPHT filtration tests&#xa0;at 160&#xa0;°C and 400 psi, along with&#xa0;shale reactivity analysis were performed to evaluate wellbore integrity. The low kinematic viscosity (1.68 cSt) and pour point (&lt; − 30&#xa0;°C) of EHB ensured excellent flowability at low temperatures, while its low acid number and high hydrolytic stability enhanced resistance to hydrolysis. Biodegradability assessment revealed that EHB achieved 62% degradation within 28&#xa0;days, indicating compliance with&#xa0; environmental acceptability criteria&#xa0;for offshore discharge. Benchmarking against a commercially available paraffinic synthetic base oil demonstrated comparable rheological and filtration performance, with all muds maintaining fluid loss below API limits. The results confirm that EHB-muds maintain stable rheological and filtration performance under low-temperature and HPHT conditions while offering enhanced biodegradability, indicating strong potential for environmentally compliant offshore deep-water drilling applications.</p>

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Performance Evaluation of a Biodegradable Ester-Based Synthetic Drilling Mud Under Deep-Water HPHT Conditions

  • 期刊论文

  • 发表日期：

    2026年4月2日

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  • Nemala Hema Durga Maheswari,
  • Geetanjali Chauhan,
  • Nulu Praveen Kumar,
  • Achanta Mounica

摘要

Offshore deep-water drilling demands environmentally compliant drilling muds that can maintain stable rheological and filtration performance under both permafrost seabed and high-pressure high-temperature (HPHT) conditions. Conventional ester-based muds often suffer from poor low-temperature flowability or inadequate thermal stability, limiting their applicability in such challenging environments. This study investigates 2-ethyl-1-hexyl butyrate (EHB), a low-molecular-weight branched ester, as a novel synthetic base oil for offshore drilling applications and characterizes its physicochemical and biodegradation properties to assess environmental compatibility and operational suitability. Drilling muds were formulated using varying mud weights, oil/water ratios, and emulsifier systems, including a natural phospholipid-based emulsifier (soya lecithin), and were evaluated for rheological performance at 3 °C and after thermal aging at 150 °C for 16 h. HPHT filtration tests at 160 °C and 400 psi, along with shale reactivity analysis were performed to evaluate wellbore integrity. The low kinematic viscosity (1.68 cSt) and pour point (< − 30 °C) of EHB ensured excellent flowability at low temperatures, while its low acid number and high hydrolytic stability enhanced resistance to hydrolysis. Biodegradability assessment revealed that EHB achieved 62% degradation within 28 days, indicating compliance with  environmental acceptability criteria for offshore discharge. Benchmarking against a commercially available paraffinic synthetic base oil demonstrated comparable rheological and filtration performance, with all muds maintaining fluid loss below API limits. The results confirm that EHB-muds maintain stable rheological and filtration performance under low-temperature and HPHT conditions while offering enhanced biodegradability, indicating strong potential for environmentally compliant offshore deep-water drilling applications.