Research On The Determination Method For The CO₂ Flooding Well Spacing In Low Permeability Reservoir

The percolation mechanism is much more complicated than that of pure water flooding in the process of CO₂ flooding in low permeability oil field, because of small pore throat of the low permeability reservoirs, large specific surface area, high flow resistance, existence of starting pressure gradient, and along with the factors of dissolution, transformation, mixing effect of carbon dioxide. According to the statistics of a number of domestic and foreign oil fields, for extra low permeability oil field, gas injection（especially CO₂） is the main technical measure to improve the development effect and establish the effective drive system.There are many studies about the reasonable well spacing in low permeability reservoir, but they are not involved in carbon dioxide flooding. At present a lot of oilfield development science and technology researchers generally use the numerical simulation method to study the optimum well spacing of CO₂ flooding in low permeability reservoirs. But because of the complexity and uncertainty of the input parameters, the numerical effect, and the limitations of the function of the numerical simulator for the carbon dioxide flooding reservoir, the reliability of the results is not satisfactory. A large number of domestic and foreign reference research results show that: It is a feasible method to research the reasonable well spacing in low permeability reservoirs by using percolation theory and reservoir engineering method.In this paper, the non Darcy flow law of low permeability carbon dioxide flooding was revealed, and the relationship between the pressure gradient and injection well spacing was analyzed by studying the starting pressure gradient and effective pressure gradient of CO₂ flooding in low permeability oil fields. This paper was divided into three parts, which are immiscible flooding, miscible flooding, immiscible flooding and miscible flooding coexistence. Percolation theory and reservoir engineering method were conducted to establish the mathematical representation of well spacing. Based on the principle of maximizing the capacity and maximizing the economic benefit, the criterion for establishing the optimum well spacing was established. Finally, taking an oil field as an example, this method was used to calculate the well spacing. And the changes of viscosity, pressure and pressure gradient in the process of oil displacement were analyzed. The three cases above were analyzed and compared, and the best result of flooding is miscible flooding. In this paper, a simple method for calculating well spacing is provided. For low permeability reservoirs of CO₂ flooding determination of the reasonable well spacing has important guiding significance...