The Effect of Weighting Agents on Sandstone Formation Damage from Water-Based Drilling Fluids

Abstract

Summary Chemical properties of a fluid used in oil and gas drilling operations are critical as they directly affect drilling performance and, most importantly, formation damage in production zones. The increased requirement for high-density fluids to maintain deeper, more complex well trajectories may translate to an increase in drilling fluid solids content when brine-weighted fluids are not compatible or readily available, as more weighting materials are added to increase density and control formation pressures. However, these weighting agents can also plug pores and cause formation damage, leading to significantly reduced productivity and the need for remediation. The objective of this study is twofold: To evaluate and compare solids invasion and damage characteristics and performance of different weighting materials in water-based reservoir drilling fluids (RDFs) and to study the solubility behavior of micronized ilmenite in different acid systems. Several fluid systems were prepared using weighting agents differing in size, morphology, and chemical nature, primarily American Petroleum Institute (API) barite, micronized barite, and micronized ilmenite. Rheological properties were measured and high-pressure/high-temperature (HP/HT) static filtration experiments were conducted to investigate filtration behavior and filter-cake thickness. A modified coreflood setup was used to simulate dynamic drilling conditions downhole and accurately measure the effect of solids on formation damage. Computed tomography (CT) scan analysis provided the extent of the damage associated with each weighting agent. Within the scope of the study and limits of the experimental setup, results showed that the formation damage created by micronized ilmenite is much lower, compared to API and micronized barite in Bandera, Berea, and Boise sandstones. HP/HT solubility reactions with different blends of acids were monitored. The best acid system was tested with a complete drilling fluid system using the mud loop to ensure the ability to remediate damage from drilling operations.