Ultra-low permeability reservoirs in the Changqing Oilfield exhibit low reservoir quality (porosity of 9–12%), low reservoir permeability (0.05 to 0.3 mD) and low reservoir pressure (about 75 to 85% of normal hydrostatic pressure). Due to these reservoir conditions and restrictions in well spacing and waterflooding patterns, it is not effective to achieve economic production by simply increasing fracture lengths using conventional stimulation techniques. An operator in the Changqing Oilfield has conducted theoretical studies and pilot field trials, integrated reservoir characteristics into fracture design considerations, and developed three unique stimulation techniques to tackle these reservoirs. The core idea of these techniques is to achieve commercial oil production by creating multiple/complex fractures and hence increasing reservoir contact area and drainage volume. The first technique is to employ oriented perforating to induce multiple hydraulic fractures for reservoirs with low deviatoric stresses. The second technique is to perform multiple treatments using particulate diversion to create multiple/complex fractures in reservoirs with natural fractures. The third technique is to perform multi-stage treatments in deviated wells to connected more reservoir volumes. Diagnostic and analysis techniques, such as net pressure matching, radioactive tracer, DSI logging and microseismic monitoring, on selected pilot wells, have confirmed that multiple fractures have been created and reservoir drainage volume has been increased using these multi-fracture stimulation techniques. From 2009 through 2012, 216 wells in ultra-low permeability reservoirs were completed using these stimulation techniques. Average oil production of these wells was increased by more than 30% in comparison with neighboring wells. These field trials have demonstrated that creating multiple fractures and enhancing stimulated reservoir volume is the key to the commercial development of ultra-low permeability reservoirs in the Changqing Oilfield.
URTeC 1578201
