High Performance Drilling Fluid Technology for Tight Oil Formation Drilling in Liaohe Oilfield

This paper introduces the characteristics of the tight oil reservoirs in the Shenbei block of Liaohe Oilfield and the studies performed on the hydration, swelling, sloughing and cave-in of the hard and brittle shales in the member 4 of the Shahejie formation in the block. Using clay mineral analysis, nano CT scan imaging and SEM, the tight oil shale was studied and the clay mineral content, average pore radius and the development of micro-fissures of the tight oil shale was determined. Laboratory tests were conducted to optimize a special compound nano plugging agent based on the characteristics of the tight oil shales. A high-performance drilling fluid with high plugging capacity, high inhibitive capacity and low erosion to borehole wall was formulated through laboratory study. The primary percent recovery of shale cuttings tested with the drilling fluid formulated was 93%, and the tertiary percent recovery of shale cuttings tested with the drilling fluid formulated was near 80%. The percent reduction of permeability was more than 50%. Field application of the drilling fluid on two wells showed that this "high viscosity high gel strength" drilling fluid successfully resolved downhole troubles such as borehole wall sloughing and cave-in, reaming and back-reaming in shale sections and pipe sticking that were previously encountered. Occurrence of downhole troubles was reduced by 17%. Time for well completion was reduced by150 d, demonstrating the effectiveness of ROP enhancement of using the drilling fluid.