Chrome-free WBM a viable option for ultra-HP/HT applications

摘要

Engineering drilling fluids for ultra HP/HT applications, particularly in sensitive ecosystems, can be a daunting proposition. Typically, oil-base drilling fluids are preferred over their water-base counterparts in applications where bottom hole temperatures (BHT) can approach 260℃ (500℉) with shut-in pressures to 25,000 psi, thereby requiring densities as high as 19 lb/gal (2.2 sg). However, more areas are prohibiting the discharge of oil-base fluids and cuttings, which increases waste management costs and potential liabilities. In some areas the use of oil- and diesel-base drilling fluids is disallowed altogether. Alternatively, a newly designed, chrome-free high density water-base drilling fluid, comprising a combination of high-grade clay, novel dispersant, and specially formulated high-molecular weight synthetic polymers, shows promise as a viable environmental, technical, and economic option for extreme HP/HT applications. A field trial in an HP/HT exploration well in tightly regulated Hungary validated the performance and environmental advantages of the new aqueous-base fluid. In this well, which targeted a tight gas reservoir, static BHT was expected to exceed 170℃ (356℉) with shut-in pressure greater than 10,000 psi.