Optimization of a Solid-Acid Precursor for Self-Destructing Filter Cake

Abstract

This paper presents technology for water-based drilling fluid that is weighted with calcium carbonate particles. This technology has functions of both drilling and completion, and can reach the total depth of maximum-reservoir-contact (MRC) wells. It creates a filter cake that prevents fluid leakoff during the drilling process, but readily cleans up the filter cake over time. This technology is based on the use of an ester, in a solid form, which hydrolyzes and produces an organic acid. The latter will dissolve calcium carbonate particles that are used as a weighting material in waterbased drilling fluids. Polylactic acid (PLA) particles were used in this study to generate lactic acid.Experiments were conducted to find an optimum particle size of the solid ester and calcium carbonate particles that should be selected as a compromise between those that are optimal for fluidloss control or filter-cake formation and those that are optimal for self-destruction at the desired time and rate. Other sets of experiments were conducted to determine the optimal temperature and soaking time required for the solid ester to hydrolyze and for the resulting acid to dissolve calcium carbonate particles.All experiments showed that in controllable conditions of temperature, acid concentration, and particle size, the cleanup efficiency exceeded 70%. The optimum particle size was found to be 50 lm for calcium carbonate and 150 lm for PLA. The optimum temperature was 230 F. These conditions will ensure high filtercake-removal efficiency, low filtrate volume, and no returneddrilling-fluid or high-viscosity problems. Ample soaking time is needed for PLA to hydrolyze and for the generated acid to remove the filter cake (i.e., 20 hours).