Development of Systematic Hydraulic Fracturing Technology for a Naturally Fractured Reservoir

Abstract Reservoir N is a typical low-permeability buried-hill fractured reservoir with oil-bearing area of 3.6Km2, OOIP of 973 × 104t and buried depth of -1700 ~ -2500m.Its oil bearing interval is longer, between 125 ~ 410m.Its average porosity is 5.1% and average permeability is 23.6× 10−3µm2. Due to the insufficient natural energy, its pressure coefficient is 0.98. As the economic yield can't be achieved by conventional technologies, the reservoir must be fractured integrally. Following technologies have been applied in the field. Based on early and proper water injection, supplementing formation energy and maintaining formation pressure, fracturing and waterflooding are combined reasonably to improve waterflooding sweep efficiency and avoid watering out and water channeling at the same time; the concept of optimizing fracturing design for high sand content, large discharge capacity, medium and low proppant concentration and medium and long fractures is established so that artificial fractures can be communicated with natural fractures and a complete interconnected system can be formed by pores, artificial and natural fractures in the reservoir; with the method of perforating short intervals, avoiding perforating long intervals and staged fracturing, the whole oil-bearing interval is divided into 2 to 4 fracturing units which are fractured from bottom to up till all the interval are fractured; silt is used as the fracturing fluid loss additive to reduce excessive fracturing fluid loss and used for propping fractures and connecting major fractures and natural microfractures. Reservoir N has been fractured for 96 times by this method with cumulative oil production of 98.3 × 104t. Field applications indicate that the method of integral fracturing development is also suitable for the low-permeability fractured sandstone reservoirs which are similar to Reservoir N and good development effects have been got.