Mesoscopic theoretical modeling and experimental study of rheological behavior of water-based drilling fluid containing associative synthetic polymer, bentonite, and limestone

Abstract

Employing an effective rheological model for the flow of drilling fluid that can accurately predict changing conditions is of significant importance in drilling fluid optimization. Traditional generalized Newtonian models cannot predict the time change condition, viscoelastic behavior, role of each component, or microstructural behaviors within the fluid. Consequently, the present research aims to develop constitutive equations in the framework of generalized bracket formalisms and the extra tensor concept that connect the microscopic and macroscopic properties and can overcome the aforementioned problems of traditional rheological models. The developed model is applicable for drilling fluid as a suspension system containing associative synthetic polymer, bentonite, and limestone suspended in water; where simple structures of flexible dumbbells, disks, and hard spheres, respectively, are representative of each component in the system. Five samples of drilling fluid with different additive concentrations were prepared and rheological testing was performed on these samples. To obtain the fixed parameters of the model, scanning electron microscope and particle size analyses were conducted on the dried powder and dispersed particles of bentonite and limestone to characterize the shape and size of the particles. The adjustable parameters of the model were then obtained by fitting it using the gathered experimental rheological data. The outcomes of the study revealed that the novel developed model can accurately predict rheological material functions, including shear viscosity and the first normal stress coefficient under transient and steady-state conditions. Furthermore, the presented model is capable of distinguishing the contribution of each component in the drilling fluid rheology.