Study on production performance characteristics of horizontal wells in low permeability and tight oil reservoirs

Abstract

Low permeability and tight oil reservoirs are rich in microscale pores and contain a large amount of dissolved gas. With the progress of production, the volatile gas gradually forms a continuous gas phase and has an important impact on the productivity of oil wells. In this paper, the characteristics of oil and gas separation in the production process of low permeability and tight reservoirs are described, a productivity prediction vector model is established considering the characteristics of starting pressure in the percolation process, and the coupled influence of "oil film thickness - high pressure effect - multi-element gas effect" on dissolved gas flow is analyzed. Results show that: (a) The horizontal section length and production pressure difference of horizontal wells are the key factors affecting the productivity of low permeability or tight oil reservoirs, while the influence of wellbore radius and reservoir thickness is not obvious. (b) The increase in the length of the horizontal section effectively increases the well control range, increases the oil drainage volume, and thus improves the productivity. (c) With the development of low permeability or tight oil reservoirs, the reservoir pressure and oil saturation have decreased. This results in a decrease in oil film thickness and an increase in volatile gas content. With the change of volatile gas pressure and the change of percolation pore size, the Knudsen number changes in a large range, resulting in the change of the microscale transport mechanism of volatile gas.