The Utilization of Self-Crosslinkable Nanoparticles as High-Temperature Plugging Agent in Water-Based Drilling Fluid

Abstract

Summary The increasing exploration of oil/gas resources in unconventional reservoirs, such as deep layers and shale formation, hinges on the development of high-performance drilling fluids under harsh environments. In this work, self-crosslinkable nanoparticles [poly(methyl methacrylate/styrene/2-acrylamido-2-methyl-1-propanesulfonic acid (PMS)/N-(hydroxymethyl)acrylamides (PMSNs)] were prepared and utilized as a plugging agent to realize micropore plugging at high temperatures. The obtained PMSN possesses long-term colloidal stability in conventional storage and high-temperature aging cases. Incorporating thermal crosslinking property brought PMSN post-crosslinking behavior during thermal treatment and improved the thermal stability, as verified by Fourier transform infrared spectrometer (FT-IR) and thermogravimetric analysis (TGA) tests. Additionally, PMSN is emulsifier-free and compatible with bentonite-based drilling fluid without foaming problems. Compared with conventional rigid nanosilica (NS) and flexible nanopolyester (NP-1), PMSN can improve the hole-cleaning efficiency of sodium bentonite (Na-Bent) dispersion by increasing viscosity and yield point (YP), especially after thermal aging. Its filtration-reduction and clay core plugging performance at room temperature are between NS and NP-1, ascribing to the rigid core and partial flexible shell structures of PMSN. However, at high-temperature, high-pressure (HTHP) conditions, PMSN with self-crosslinked structures have superior micropore plugging performance over NS and NP-1. A statistical-significant model was established based on response surface methodology (RSM) to illustrate the main and interactive effects of PMSN dosage, aging temperature, and time on the HTHP micropore fluid loss. The optimal plugging can be obtained after high-temperature aging when self-crosslinking happened. The specific self-crosslinking plugging mechanism of PMSN is the combination of interior self-crosslinking in water and interparticle crosslinking in the deposited plugging layer.