Development of and Study on an Anti-sloughing Plugging Agent Used in Drilling Fluids to Strengthen Coal Beds

To avoiding borehole wall collapse drilling in brittle coal beds full of micro fractures, an emulsion anti-sloughing plugging agent has been developed with hydrophilic monomers and hydrophobic monomers through O/W emulsion polymerization. Laboratory studies showed that the dispersion of the anti-sloughing plugging agent has particle sizes ranging in 0.1-1.5 μm, which match the sizes of micro fractures developed in the coal beds, meaning that the micro fractures can be effectively plugged with the plugging agent. This plugging agent can render the surface of coal beds oil-wettability and thus greatly mitigates the dispersion of coals in water. In bentonite slurry, the plugging agent can reduce API flter loss, thereby enhancing the plugging performance of the bentonite slurry. Coal samples rinsed in the solution of the plugging agent had their compressive strength increased. Drilling fluids treated with the anti-sloughing plugging agent have good rheology and fltration property, and cause low damage to coal beds. Percent recovery of permeability of coal samples tested with water can be as high as 95.4%. A drilling fluid treated with the anti-sloughing plugging agent was used on the well SX-2** to drill the coal bed formations from 795.00 m to 1088.00 m. The drilling operation and coring job was successful. Percent recovery of cores taken from the coal section was 96.51%, and the integrity of the coal formations was maintained pretty well.