Development of water-based drilling fluid used in unconsolidated sandstone reservoir

Abstract

ABSTRACT According to the fact that there is some little research on drilling fluid used in unconsolidated sandstone reservoir while conventional drilling fluid can not meet the requirements, we developed a new kind of water-based drilling fluid system. In this paper, bentonite, filtrate reducer, inhibitor, and other additives were optimized according to the characteristics of unconsolidated sandstone formation and several properties like rheology, filter loss, inhibition, and so on. A new drilling fluid system was developed and it was finally determined to be 5% Na2CO3 + 4% bentonite +0.2%PAC+ 0.7%FLA1 + 2%IHT1 + 3%GSJ +0.8% WHA1. The density, apparent viscosity, plastic viscosity, and yield point of this system were 1.18 g/cm3, 38.2 mPa·s, 24 mPa·s, and 17.2 Pa, respectively. Its filter loss was 6.2 ml, thickness of filter cake was 0.5 mm, roll recovery of rock samples was 88%, and the expansion amount was 0.18 mm. In immersion experiment, there was no obvious cracks on core samples. The result showed that this drilling fluid system can effectively clean the unconsolidated sandstone borehole and its filter loss performance, rejection capability, and antipollution properties were pretty good.