Modified Nanopolystyrene as a Plugging Agent for Oil-Based Drilling Fluids Applied in Shale Formation

Abstract

Most nanoplugging agents have high surface free energy and tend to aggregate in oil-based drilling fluids (OBMs), failing to plug the nanopores in the formation. This paper introduces the synthesis and application of a surface-modified nanoscale polystyrene (NS) as a plugging agent for OBMs. With oleic acid acting as the surface modifier, the surface free energy of the NS can be effectively reduced, which is a crucial step in enhancing its dispersion stability in mineral oil. Besides, due to the nanoscale size and low surface free energy, NS adsorbing onto the rock surface could improve the contact angle of the mineral oil on the rock surface, reduce the imbibition amount of oil into the rock, and maintain the mechanical stability of the rock. The structure of NS was characterized by infrared spectroscopy and transmission electron microscopy. Thermal gravimetric analysis demonstrated that NS could resist up to 252 °C. The particle size distribution test showed that NS could maintain the nanoscale dispersion in mineral oil. NS could also increase the contact angle of mineral oil on the rock surface from 12 to 61°and reduce the oil spontaneous imbibition amount by 52.7%. After the addition of 2% NS to the base mud, the permeability plugging apparatus filtration loss was reduced by 67% compared with that of the base mud without NS, and in the pressure transmission test, the downstream pressure was still kept constant with no noticeable change after 60 h, showing an excellent plugging effect. Besides, after the rocks were immersed in the base mud and base mud containing 2% NS, the uniaxial compressive strength of the rock declined by 25.41 and 10.76%, respectively, indicating that NS could effectively alleviate the mechanical stability decrease of the rock.

Novel Use of a Superhydrophobic Nanosilica Performing Wettability Alteration and Plugging in Water-Based Drilling Fluids for Wellbore Strengthening

“…Thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) are widely used to evaluate the high-temperature resistance and characterize the components of the substance. 44 Figure 7 illustrates the weight decrease amount and weight decrease rate of SA with temperature increase. A slight decrease in weight occurred when the temperature was below 150 °C, resulting from the absorbed water evaporating.…”

“…Surface energy represents the net attractive force of the particle, influencing the dispersion stability. 44 When the surface energy is high, the attractive forces among particles are so large that particles tend to aggregate.…”

“…The surface energy of the hydrophobic nanomaterial was decreased through surface modifications, which would improve the nanoscale dispersion stability and favor the plugging performance. 44 Unfortunately, no related tests were performed. Second, how these modified nanomaterials inhibit shale hydration was not fully discussed.…”

“…First, the above research did not evaluate the plugging performance of the hydrophobic nanomaterials. The surface energy of the hydrophobic nanomaterial was decreased through surface modifications, which would improve the nanoscale dispersion stability and favor the plugging performance . Unfortunately, no related tests were performed.…”

Improvement of Emulsion Stability and Plugging Performance of Nanopores Using Modified Polystyrene Nanoparticles in Invert Emulsion Drilling Fluids

“…SBR/SiO 2 can effectively reduce the filter loss and pressure transmission, stabilizing the wellbore. Geng et al ( Geng et al, 2021 ) synthesized a surface-modified nanoscale polystyrene material as a plugging agent for OBFs, which can improve the contact angle of the mineral oil on the rock surfaces, reduce the amount of imbibition of the oil into the rock, and maintain the wellbore stability. Xie et al ( Xie et al, 2015 ) synthesized a hyperbranched polyamine (HBPA) material with an average particle size of 36.7 nm.…”