Development and Evaluation of Low Density Solids-free High Temperature Drilling Fluid

Organic salts are presently used to improve the high temperature stability of solids-free drilling fluids, which have higher density because of the presence of organic salts. Higher density plays a negative role in the protection of deep high temperature lowpressure reservoirs. A solids-free high temperature drilling fluid, WGX, was recently formulated with a newly developed viscosifier SDKP, and a series of selected additives such as antioxidant, filter loss reducer, lubricant and inhibitive agent. WGX had a density of 1.02 g/cm³ and remained stable at 190℃. Performance evaluation showed that WGX had good high temperature rheology and good carrying capacity at high temperature. Permeability test gave a percent permeability recovery of greater than 90%. The rheology of WGX remained satisfactory even when contaminated with 5% NaCl or 10% clays. Percent rate of swelling of cores tested with WGX was only 7.22%, and hot rolling test showed a percent recovery of shale samples of 89.33%. WGX tested on an extreme lubricity tester showed that the extreme frictional coefficient was only 0.085.