Development and evaluation of graphene nanosheets as a novel micro-nano plugging agent for oil-based muds

Abstract

Although there are abundant shale gas resources in China, shale gas is generally buried much deeper than foreign countries. For large-scale development, there are still many core technologies that have not yet been solved. In this paper, we have analyzed microstructure of formation rock and its mineral composition, and the mechanism of wellbore instability is revealed by studying the petrophysical properties and characteristics of the wellbore instability strata in the Changning-Weiyuan area. The laboratory innovatively constructs the “solid phase intercalation-liquid phase expansion stripping method” and obtains high-quality graphene nanosheets. The results of the performance test and the HTHP filtration test on the graphene nanosheets show that it achieves the lowest HTHP filtration loss (8.0 mL) among tested additives, outperforming super-fine CaCO₃(8.6 mL) and conventional agents (9.2 mL), while minimally affecting rheology. Other performance tests indicate that high-quality graphene nanosheets made by our laboratory can be well dispersed in solvent with almost no obvious aggregation and it has the median particle size ranges from 212 nm to 228 nm, which means it has perfect ability to plug micro-crack in the Changning-Weiyuan area. The oilfield application shows that adding 0.75% graphene nanosheets to the field mud significantly enhanced wellbore stability, achieving zero mud loss and a 94.6% drilling rate in the target zone, while reducing HTHP filtration to below 2.4 mL.