Mechanism Study Of CO₂ Miscible Displacement In Low Permeability Reservoirs

With the development of exploration and technology at the current time, low-permeability oil reserves account for an increasing proportion. Rational development of low permeability oil fields is of great significance, which alleviates tension in China's oil reserve stocks and ensures sustainable and stable development of the oil business. However, Low permeability reservoir properties,such as porosity and permeability are relatively poor, in case that, the production per well is low, development is difficult. With the full use of carbon dioxide can enhance oil recovery at low permeability oil fields.Considering the amendment of crude oil viscosity,CO₂ miscible displacement model is built. The characteristics of low permeability reservoir is described by low porosity. The miscible displacement model at low permeability reservoir, where gas adsoption is taken into account , is solved not only by Barakat-Clark finite difference scheme,which is also used by the miscible displacement model at low permeability reservoir, where gas adsoption isn't taken into account,but also by the display of the central difference scheme. The effects of various properties and process parameters such as Peclet number, injection gas pressure , injection velocity ,porosity and crude oil viscosity on gas adsorption ,CO₂ breakthrough and the effect of reducing oil viscosity are investigated and discussed. The effects of different kinds of difference scheme on the model results are also analysed. Stability of difference schemes is verified according to Gerschgorin Disk theorem.The first derivative and second derivative approximation Difference are obtained by Taylor formula and by using linear operator; Truncation error of central difference scheme and the Barakat-Clark finite difference is solved by using Taylor formula, multi-function differential; The coefficient matrix eigenvalue is solved according to Gerschgorin disk theorem.The results show that, smaller Peclet number can cause large gas diffusion velocity, higher injection velocity can cause large displacement velocity and CO₂ large adsorption and swelling at the front end of the core; higher inlet pressure can cause large displacement velocity and CO₂ large adsorption ,and also overcome the resistance efficient; higher porosity not only can make rock surface smaller,which can cause smaller adsorption quantity,but also means that reservoir permeability is higher and fluid flow is better. The effects of the different kinds of difference schemes on the results of the models are greater.The smaller Peclet number and the higher injection velocity ,injection pressure and porosity can make time of CO₂ swelling at the front end of the core earlier. When crude oil viscosity is greater, the mixture viscosity is changed greater. The order of the central difference scheme and the Barakat-Clark finite difference is the same;When r is equal to 0.8,two kinds of difference scheme are stable.The research has theory direction for the reasonable development of low permeability reservoir.