Study of Lost Circulation Protection and Control Drilling Fluid for Induced Cracks

Abstract

Serious mud losses happened at Huaqing Oil Field due to the induced fractures. The current bridging plug agent is poor adaptable to the fracture and pore size. The bridging material, polymeric adsorbent materials and filler materials and particle size distribution were optimized. As a result, the bridging materials were compounded of the rubber particles with different particle size, in which the percentage of rubber particles of diameter 0.6–1.0, 1.1–1.5, and 1.6–2.0 mm was 30, 30, and 40%, respectively. The polymer adsorption material was CDL-1. The filling material consisted of 30% vermiculite with particle of diameter 0.4–0.5 mm, 5–10% of mica, 5–10% of sawdust, 20–50% of the bridge plug agent QD-1, 20–30% of QD-2, and 1–20% of the one-way pressure sealer DF-A. By orthogonal experiments, the plugging drilling fluid adaptable to leakproof was determined by adding 2% rubber particles, 0.2% CDL-1, and 3% fill material in the base slurry (water + 0.3% PAM + 4% bentonite). The viscosity of the drilling fluid was of 10 MPa s, the yield point was of 3 Pa, the pressure capacity was of 4 MPa, and the minimum closure time was of 10 min. The field test proved the drilling fluid could seal the lost layer in a relatively short time effectively.