Experimental screening of beneficiated Nteje clay–bentonite blends for water-based drilling fluid formulations

Abstract

Reliance on imported bentonite for water-based drilling fluid formulation poses economic and supply-chain challenges in many developing oil-producing regions. This study experimentally screens the performance of beneficiated Nteje clay (NC3) as a partial replacement for foreign bentonite (FB) in water-based drilling fluid formulations and provides a preliminary raw material cost assessment of the resulting blends. Mud samples were formulated at a constant total clay concentration of 22 g per laboratory barrel, with FB progressively substituted by NC3 from 0 to 100%. Rheological, filtration, and chemical properties were measured in accordance with API RP 13B-1 using standard viscometer and low-temperature low-pressure filtration tests, while flow behavior parameters were derived from viscometer data. A preliminary raw material cost analysis was performed using a weighted-average clay cost model scaled from laboratory-barrel to estimated well-level clay consumption. Results indicate that drilling fluids containing up to 50–60% NC3 maintain API-compliant performance, including 600 rpm viscometer readings ≥ 30 cP, plastic viscosity within 8–10 cP, YP/PV ratios within the recommended screening range, and pronounced shear-thinning behavior. Filtration performance remains acceptable within this substitution range, with fluid loss below 15 mL and filter cake thickness less than 2 mm. Higher NC3 substitution levels result in reduced yield point and gel strength, near-Newtonian flow behavior, and excessive fluid loss. The preliminary raw material cost analysis showed that partial replacement at 50–60% NC3 reduces estimated clay cost per well by approximately 33–39%. The study establishes beneficiated Nteje clay as an effective bentonite extender, offering a technically sound and cost-efficient pathway for sustainable drilling fluid formulation.