Assessment of Oil Reservoirs Suitable for CO2 Flooding in Mature Oil Reservoirs, Changqing Oilfield, China

Abstract

Most oil reservoirs in Changqing Oilfield area are low permeability. After several ten years of production, the effect of water flooding becomes worse and worse as the reservoir enters middle development stages. CO 2 flooding is an important method for oil fields in the future to enhance recovery factor. In this paper, based on the data of 253 mature oil reservoirs, a set of potential evaluation method for CO 2 flooding were builded to assess the potential of CO 2 EOR in Changqing Oilfield.A numerical model was established to study the effect of the related factors to CO 2 miscible flooding and immiscible flooding. These factors are reservoir properties (thickness, Angle, temperature, pressure, depth), rock physical property (porosity, permeability, saturation, permeability differential, fracture development degree and permeability) and fluid properties (viscosity, density). Technical and economic benefits is assessed, to determine screening criteria and index for CO 2 miscible flooding, their relative importance, and the index weights. Using comprehensive fuzzy evaluation method, this paper sets up a comprehensive evaluation method of CO 2 miscible flooding and immiscible flooding, Which suit for the different blocks of Changqing Oilfield. Comprehensive evaluation value of reservoir was calculated, according to the evaluation method.With evaluation value of 0.53 as a boundary, CO 2 flooding potential assessment of Changqing Oilfield has been done. Among 253 reserviors, 213 reservoirs are suitable for CO 2 flooding EOR, which accouts for 84% of the total number of reservoirs within the block. The geological reserves which is suitable for CO 2 flooding could be 25.05ϫ10 8 t, equaling to 80% of the total reserves of Changqing Oilfield. Therefore, CO 2 flooding has a good application prospect in Changqing Oilfield, and it would bring huge economic benefits to Changqing Oilfield.