Investigation of Poly(MM-EM-BM) as Nanosealing Materials in Oil-Based Drilling Fluids: Synthesis and Evaluation

Abstract

Nanosealing technology has become the key to overcoming the wellbore instability problem in deep and ultradeep shale formations. In this Article, the terpolymer poly(MM-EM-BM) was synthesized from methyl methacrylate, ethyl methacrylate, and butyl methacrylate by a Michael addition reaction. The poly(MM-EM-BM) nanoparticles were investigated by Fourier transform infrared spectroscopy, laser scattering analysis, and thermogravimetric analysis. The results imply that the particle size range of poly(MM-EM-BM) is between 33.90 and 135.62 nm and the average diameter is about 85.95 nm at room temperature, which can maintain excellent stability at 382.75 °C. The effects of poly(MM-EM-BM) on the properties of oil-based drilling fluids (OBDFs) were ascertained through experiments on the rheological performance, electrical stability, and high-temperature and high-pressure (HTHP) filtration loss. The results suggested that when the amount of added poly(MM-EM-BM) increases, the apparent viscosity, plastic viscosity, dynamic shear force, and demulsification voltage of the drilling fluids will increase correspondingly; in contrast, the HTHP filtration loss gradually decreased. When poly(MM-EM-BM) is added at 0.75%, the kinetic-to-plastic ratio of the drilling fluids is 0.24 and the filtration loss is 0.6 mL, showing excellent overall performance. The drilling fluids have a good rock-carrying ability and water loss wall-building property. The sealing performance and mechanism of poly(MM-EM-BM) were researched by the method of a sealing performance test under high temperature. The results indicated that the more poly(MM-EM-BM) used, the higher the sealing efficiency of the mud cake and the core as the sealing medium. When poly(MM-EM-BM) was added at 0.75%, the sealing rates of the mud cake and the core as the sealing medium reached the maximum sealing rates of 40.30% and 91.48%, respectively. When poly(MM-EM-BM) enters the core nanopore joint for a certain distance under formation pressure, a tight sealing layer will be formed to effectively prevent the entry of filtrate. Poly(MM-EM-BM) as a potential oil-based nanosealing agent is expected to solve the problem caused by wellbore instability in shale horizontal wells.

Experimental Water Activity Suppression and Numerical Simulation of Shale Pore Blocking

“…Currently, the understanding of the sealing effects of nanoparticle drilling fluids on shale pore space is primarily based on physical experimental data [25][26][27][28][29]. However, the mechanisms governing the transportation, dynamic stacking, and microscopic sealing of nanoparticles in drilling fluids after entering the shale pore space remain unclear.…”