Graphene Slurry Plugging Agent for Water-Based Drilling Fluid

Summary During the process of solving the wellbore instability problem in shale sections and the reservoir damage problem in deep interbedded claystone and sandstone sections, one must examine the research direction of strengthening the rapid plugging of microfractures and micropores. Graphene-based products are capable of plugging microfractures in low concentration due to their excellent micronanometer size and lamellar membrane structure. In this study, we develop a liquid-phase shear stripping methodology with relatively acceptable cost to produce graphene with few-layered structure. Based on the shear strengthening function, natural graphite is exfoliated into graphene. To make sure the material was applied in water-based drilling fluid, the hydrophilic polymers, such as carboxymethyl cellulose (CMC), were mixed during the subsequent rotational stripping process, and the stable graphene slurry was prepared. CMC can increase the viscosity of the slurry, thus slowing down the sedimentation rate of graphene, which is conducive to the stable dispersion of graphene in the solution. The hydroxyl and carboxyl bonds in CMC can interact with the surface functional groups of graphene to form hydrogen bonds or π-π stacking, thereby enhancing the adhesion between graphene. The long-chain structure of CMC molecules can effectively prevent aggregation and stacking between graphene sheets and improve the dispersion and stability of graphene. CMC can also form a crosslinked network structure with graphene, thereby improving the colloidal stability of the system. The performance evaluation shows that the median particle size (D50) of the slurry is about 6 μm, which has a good effect on reducing fluid filtration and inhibiting shale expansion. The evaluation using permeability plugging apparatus shows that the slurry can effectively plug the micropores in the ceramic filter. The field applications illustrate that the graphene agent has good compatibility with water-based drilling fluid, which is able to improve the plugging effect of drilling fluid, helping to solve the problem of wellbore instability and reducing the reservoir damage caused by mud filtrate invasion.