Evaluation of Polymer-Based Drilling Fluid Additives Performance Under Harsh Subsurface Conditions

Abstract

Drilling fluids are designed carefully to yield filter cakes with good performance. Fine-scale assessments have revealed that the filter cake has two distinct layers: an internal layer that is close to the surface and an external layer that is close to the drilling fluid. Polymer additives have been used as lost circulation materials. They provide the means to bridge spaces in the rock in order to minimize the fluid invasion and formation damage. The performance of the polymer-based filter cake changes under harsh, high-temperature subsurface conditions. It is difficult to extract the polymer layer while maintaining its integrity so that it can be used in experimental assessments. Molecular simulation offers an alternative means of performing a thorough evaluation of the polymer layer at high temperatures. In this study, three common polymer additives, starch, carboxymethyl cellulose (CMC), and sodium polyacrylate (SPA), were re-created on a computational platform. The structures were subjected to a thorough analysis to extract various characteristics such as their mechanical strengths and interactions with the drilling fluid base (i.e., water). The results revealed that the three polymers maintain reasonable integrity at temperatures up to 400 K (starch and SPA) and 350 K (CMC). The yield strength of the starch decreased from 0.37 GPa to 0.21 GPa as the temperature increased from 300 K to 450 K, while it decreased from 0.66 to 0.38 for the SPA at the same range of temperature. The toughness of the starch and polyacrylate decreased by half within this temperature range. The temperature had a more pronounced impact on the stability of the CMC structure. Considering three polymers with different chemical characteristics allowed to show that the integrity of a polymer is linked to its molecular structure. The findings reported in this paper cast additional light on high-temperature polymer additive performance. The framework established in this study can be applied to other additives to support optimized drilling operations.