Case Study Development of Low-Permeability and Low-Pressure Reservoir Block Bao14 by Fracturing and Water Injection

Abstract

Abstract Block Bao14 has a burial depth of −850~-1420m, porosity of 17.0%, permeability of 27.0×10−3μm2 and orginial formation pressure of 12.3MPa. However, the pressure in the reservoir declines very quickly, so it is a typical low permeability and low pressure sandstone reservoir. The paper will present the developmemt situation of the reservoir with both fracturing and water injection. Due to the existence of the induced fractures, this kind of development mode poses great risks, i.e. premature water-flooding or water channeling may happen to the oil wells if the azimuths and lengths of the fractures are not compatible with the injection- production patterns and parameters. The following methods are adopted to solve the problem. The azimuths and lengths of the fractures are measured by the electric resistivity tomography and microearthquake method to be the bases for adjusting the injection-production patterns and designing the injection-production parameters. The relationships between the injection-production parameters, fracture parameters of the oil or water wells at different locations in the well pattern and the sweep efficiency, production and watercut under the conditions of induced fractures are simulated and calculated and the fracture lengths and flow conductivity of the oil and water wells are optimized. With the application of low temperature gel break activator, the activity of APS is activated at low temperatures and the process of peroxy release by APS is controlled to control the chemical reaction rate so that the gel breaking time of the fracturing fluid can be controlled to ensure quick gel breaking of the fracturing fluids at low temperatures. An integral pipestring for fracturing and flowback is used. With multistage gas lift valves installed at different locations on the fracturing pipestring, continuous flowback of the fracturing fluid can be realized, improving the flowback rate and efficiency. Resin coated sands are tailed in to effectively contol the the flowback of proppants after fracturing without any effects on fracturing stimulation results. Based on fracture azimuth and length, alternate water injection is applied horizontally and cyclic water injection is applied vertically and intermittent water injection is applied in some heavily flooded areas, greatly improving water injection sweep efficiency and effectively controlling the premature occurrence of water-flooding and water channeling. 20 wells have been put (converted) into water injection in Block BAO14 under this mode with water injection of 184m3/d and cumulated water injection of 36.7761×104m3. Altogether 78 oil wells have been put into production with fluid production of 605t/d, oil production of 289t/d, overall watercut of 52.17%, oil recovery rate of 2.61%, oil recovery rate for the residual recoverable reserves of 38.4%, cumulated oil production of 29.1728×104t and degree of reserve recovery of 7.76%, achieving favourable overall development results of the block.