Filtration of Biodegradable Fiber-Containing Drilling Fluids for Offshore Shallow Weak Formations

Fiber-containing drilling fluids are expected to improve hole cleaning efficiency and have filtration properties that help to form a strong mud cake on the borehole wall. The objective of this study is to evaluate the filtration properties of drilling fluids containing a novel biodegradable polymer fiber. The novel 100% bio-based polymer, named PHBH (TM), biodegrades easily in a seawater environment. The filtration properties of drilling fluids containing PHBH fibers were investigated through static filtration tests using an API (LPLT) filter press and a high-temperature and high-pressure (HPHT) filter press. The HPHT tests were conducted at 93°C (200°F). The tested base fluids contained 1.5wt% of bentonite or sepiolite clay, and 0.1 to 0.4wt% of polyanionic cellulose (PAC-HG) as a viscosifier. Sepiolite was considered since it is more thermally stable than bentonite. From the results of API and HPHT filtration tests, adding 0.4wt% PHBH fibers reduced the amount of filtrate by approximately 5 to 7%, and the thicknesses of mud cake by approximately 24 to 34%. Among the 3, 5, 10, and 14 mm-long fibers tested, 14 mm long fibers resulted in the maximum reductions in filtrate and mud-cake thickness. Analysis of the solid concentration in the suggested that thin and strong mud cakes might form by adding the PHBH fibers for both bentonite- and sepiolite-based fluids. Compared to the existing commercial fiber additives, the novelty of application of the new biodegradable fiber-containing drilling fluids to prevention of lost circulation or borehole wall strengthening in offshore shallow weak formations is highly environmentally-friendly for sustainable oil and gas developments. The biodegradable fiber-containing fluids can be applied in various uses like completion fluid, cementing spacer, etc.