A novel graphene grated polymer as shale inhibitor in drilling fluids and study of mechanism

During the drilling process, the hydration and expansion of shale are one of the main reasons for wellbore instability, which can lead to stuck drilling and economic losses. A novel shale inhibitor (ADG) was successfully synthesized by thermal polymerization using Acrylamide (AM), Dimethyl diallyl ammonium chloride (DMDAAC) and Graphene as raw materials, Ammonium persulfate, and Sodium bisulfite as initiators. In order to study the structural characteristics of ADG, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Thermogravimetric loss test (TG), and Scanning electron microscopy (SEM) test were conducted. Simultaneously, linear swelling test, mud making test, sedimentation test, contact angle test, and montmorillonite (MMT) impregnation test were conducted to evaluate its inhibitory performance. ADG can reduce the expansion height of bentonite test blocks from 6.4 mm to 2.06 mm. After adding ADG, the settling speed can be effectively accelerated, with a settling time of only 15 min and a settling height as low as 60 mm. SEM analysis revealed that ADG had a regular flake-like structure. Compared to conventional shale inhibitors, ADG can increase the contact angle of bentonite test blocks from 26.8° to 46.8°, improving their hydrophobicity. Mechanistic studies suggested that ADG molecules could adsorb on the shale surface and block surface pores, reducing the contact area between shale and water. Additionally, small ADG molecules could penetrate the pore interiors and form hydrophobic films. The dual mechanism of ADG, inhibiting hydration and providing physical blockage, further demonstrated its excellent inhibitory performance.