Study and Application of Low Solids Ultra-high Temperature Water Base Drilling Fluid

A low clay content and low solids ultra-high temperature water base drilling fluid was engineered using optimized polymer viscosifier SDKP, high temperature filter loss reducer, oil-soluble plugging agent, lubricant, high temperature protective agent and water block preventer, based on an analysis of the characteristics of the reservoir in Nanpu, Jidong. Laboratory experiments showed that after 16 hours of aging at 165℃, 1% SDKP water solution still retained 20% of its original viscosity. A combination of two filter loss reducers, SD-101 and SD-201, remarkably reduce the filter loss of a 1.0% bentonite slurry. HQ-10, an oil-soluble plugging agent, can remarkably reduce the HTHP filter loss of drilling fluid. This drilling fluid remained stable at 235℃. At 200℃, the plastic viscosity was 15 mPa.s, satisfying the needs for carrying drilled cuttings. The drilling fluid maintained good rheology even contaminated with 10% NaCl, 2% CaCl₂, or 10% inert clays. In inhibition test, the percent reduction in core swelling was 78%, and the percent recovery of cores increased from 8.24% to 84.45%. The application of this drilling fluid in the exploration well Nanpu3-82 showed that, at 220℃ (bottom hole temperature), the rheology of the fluid was stable the API filter loss remained unchanged, good carrying capacity of the fluid was realized. Well Nanpu3-82 was successfully drilled to 6,037 m, and had a liquid production of 43.20 m³/d.