Evaluation of Sawdust and Wood Ash Composite as Filtration Loss Additives in Oil-Based Drilling Fluid

Abstract

Conventional oil-based drilling fluid (OBM) additives are predominantly synthetic, costly, and environmentally hazardous. More concerning is that their disposal leads to severe environmental degradation, contributing to soil and water contamination. The design of OBM is very delicate, since it is primarily desired to handle troublesome scenarios beyond the effectiveness of WBM, specifically in the loss of filtrate volume to the formation. This study, therefore, evaluated a composite of equal proportions of sawdust and wood ash as an eco-friendly filtration loss additive in OBMs. The sawdust was sourced locally and processed for mud formulation by fine sieving and into wood ash by incinerating in a furnace at 650 °C. Five mud samples containing increasing concentrations of the composite additive (0, 5, 10, 15, and 20 g) were prepared according to API specifications and tested for rheological and filtration properties at room temperature. Results demonstrated that the composite addition over the range progressively increased plastic viscosity from 44 to 81 cP, apparent viscosity from 81 to 127.5 cP, yield point from 74 to 93 lb/100 ft², and gel strength from 8 to 15 lb/100 ft² and 13 to 20 lb/100 ft², at 10 seconds and 10 minutes, respectively. Crucially, API fluid loss at 30 minutes significantly decreased from 22.0 to 15.0 mL, and mud cake thickness reduced from 1.40 to 0.37 mm. Mud pH also increased remarkably to 12.0, confirming the consistency with the alkaline oxide content of wood ash. These results confirm that the sawdust-wood ash composite effectively controls filtration loss and improves rheological performance in OBM. A concentration of 10–15 g of the composite is recommended for optimal drilling efficiency and minimal energy consumption. This study offers a low-cost, biodegradable alternative to conventional synthetic additives for drilling operations.