Evaluating the effect of unmodified and modified starch (EDTA-DSD) as fluid-loss control additives in locally-sourced bentonite water-based drilling mud

Abstract Drilling oil and gas wells for hydrocarbon exploration involve high fluid loss costs. Minimizing the fluid loss is crucial to the drilling process to preserve the mud's qualities and to avoid formation impairment. Research has shown positive use of carboxymethylcellulose (CMC) and imported bentonite in the formulation of water-based mud to minimize fluid loss, however, increases the operating cost while the local bentonite has shown increased filtration losses. The aim of this study is to evaluate the rheological and filtration properties of water-based muds formulated using unmodified and modified starch with ethylenediaminetetraacetic acid (EDTA-DSD), a locally sourced material as a fluid loss additive and hyperdrill as a viscosifier at low-pressure low temperature (LPLT) and high-pressure high temperature (HPHT) conditions, and their performances were compared with CMC as reference fluid loss additives. Thermogravimetric Analysis (TGA), Scanning Electron Microscope (SEM) were harnessed to study the properties of these starches while the starch modification was achieved through acetylation and carboxymethylation. Full-set measurements of laboratory tests were conducted to evaluate the influence of adding 0.5-2g of CMC, unmodified and modified starch to the mud samples respectively, and measurements were taken using mud balance, viscometer, low-pressure and low-temperature filter press, chemical titration, and other standard drilling fluid laboratory equipment as recommended by API. Result showed that Plastic viscosity, PV for unmodified starches ranged from 14-17cP, Yield point, YP ranged from 25-31lb. /100ft2,filtrate volume ranges from 18-31ml at LPLT and 30-43ml at HPHT while PV for modified starches ranged from 14-15cp, YP ranged from 27-31lb. /100ft2, filtrate volume ranges from 17-31ml at 100psi and 19-43ml at 500psi of pressure. Experimental results indicate that the filtrate volume and cake thickness compare favorably with CMC, has the capacity to withstand HPHT conditions and are within the American Petroleum Institute specification for water-based mud. Thus, demonstrate its suitability for current and future exploration and exploitation of oil and gas resources.