Enhanced Well Productivity Potential from a New High-Density Reservoir Drilling Fluid

Abstract

A new reservoir drilling fluid system utilizes a nonbiopolymer, acid- or enzyme-solubl e polymer that serves both as viscosifier and fluid-loss additive when combined with activated magnesium oxide and a divalent-catio nbased brine. The fluid shows a unique shear-thinning rheological profile featuring relatively low, high-shear-rate viscosity along with relatively high, low-shear-rate viscosity. As a result, effective hole cleaning is provided without generating excessive high-shear-rate viscosities that lead to disproportionate equivalent circulating densities. The new fluid system is based on the higher density, divalent-cationcontaining brines (utilizing CaCl2, CaBr2, CaCl 2 / CaBr2, ZnBr2 / CaBr2 and ZnBr2 / CaBr2 / CaCl2) in the 11.5 to 17.5 lb/gal density range. The total amount of the sized CaCO3 bridging particles is kept relatively low, 13 to 35 lb/bbl, so that thin, chemically removable filter cakes are produced. This bridging particle matrix size distribution is designed according to the ideal packing sequence for optimizing sealing and producing a minimally invading (well productivity enhancing) fluid.