Study and Application of Drilling Fluid Technology for Stabilizing Fractured Formations in Shunbei Oilfield

Geological study, drilling fluid measure and optimization study and field application of the research results were conducted to resolve the problems such as wellbore instability, pipe sticking and drags encountered in drilling the fractured formations in several wells in Shunbei oilfield. It was found in the studies that the lithology of the fractured formations was non-clay minerals, and invasion of the mud filtrates into the fractured formations makes the in-situ pore- and fissure-network communicated with each other and produce induced pressure inside the pores and fissures, reducing the cementation strength between bedding plains. The formations with mud filtrate invasion are thus becoming loosened, hence resulting in large-scale caving, sloughing and even pipe sticking. To drill this non-clay fractured formations with stress concentration, effective plugging of the formations with submicron-micron (0.1-100 μm) sized particles to contain the invasion of mud and/or mud filtrates into the formations is necessary, and the drilling fluid should also have good cuttings carrying capacity. Laboratory optimization of the drilling fluid previously used to drill the fourth interval of the well gave birth to a drilling fluid suitable for drilling the fractured formations. In the whole process of drilling the fourth interval, no sloughing or caving, drag and over-pull have ever happened, and the well was successfully drilled to the designed depth of 8014 m in a record-setting short time of reservoir drilling in this area. Filed application of the optimized drilling fluid on the well Shunbei-Y showed that the borehole wall stabilizing drilling fluid had excellent properties. It can be used to stabilize the fractured formation during drilling, and is worth popularizing.