Development Of Shale Stabilizer By Grafting Hyperbranched Polymer Onto Nano Silica

Shale wall instability has been a main technical problem to be solved during the drilling process.Because shale is rich in micro-nano pores and micro-fissures,the conventional plugging agents cannot block them effectively.Nanomaterial particles are easily attracted to each other to form agglomerates because of their large surface energy,which makes it difficult to be applied directly in drilling fluids.Therefore,this paper proposes a new idea of grafting the hyperbranched polymer onto nanosilica and combining their properties to realize the physical plugging and chemical inhibition.In this paper,the hyperbranched polyamines were firstly optimized with suitable molecular structure and superior inhibitory properties.Then the hyperbranched polymer was grafted onto the nanosilica to obtain a new type of shale stabilizer?S-O-SiO₂?through the two-step modification method.The first step is modifying the nano silica by using silane coupling agent.The second step is grafting the optimized hyperbranched polymer onto nano silica.The S-O-SiO₂ was characterized by test methods such as FTIR,thermogravimetry,size distribution and so on.The inhibitory and plugging performance were evaluated using shale expansion experiment,core self-priming experiment and other experiments.The mechanism of shale stabilizer was explored through particle size distribution testing,XRD,FTIR,SEM,etc.The results showed that the particle size of the S-O-SiO₂ was about 240 nm and the Zeta potential in the water was about 17 mV.The inhibition performance and plugging performance of the S-O-SiO₂ were greatly improved compared with the nanosilica,achieving the dual functions of chemical suppression and physical plugging.The amine group of the S-O-SiO₂ generates positively charged ammonium ions after partial protonation reaction with water,which adsorb on the negative surface of shale by electrostatic action.The polymer end of the S-O-SiO₂ molecule can enter the clay layer,constraining the adjacent clay sheet effectively and making it difficult for the water molecules to enter,and inhibit the hydration expansion and dispersion of the shale.At the meantime,S-O-SiO₂ can reduce the permeability of shale and block the micro-nano pores and micro-fractures of shale.The two sets of water-based drilling fluid systems with strong plugging and inhibition function optimized with S-O-SiO₂ as the main treatment agent had stable rheological fluid loss properties before and after 120°C/16h hot rolling,good lubricating properties,and better inhibition and sealing performance.