Abstract:

In order to accurately describe the change law and influencing factors of reservoir seepage flow near injection wells in low permeability reservoirs, a well test analysis method for composite reservoir with dynamic non-Darcy effect outside injection wells was constructed. Firstly, Darcy flow is considered as the inner seepage mode, and non-Darcy flow as the outer seepage mode composed of starting pressure gradient effect and dynamic permeability effect. Secondly, numerical method is used for discrete solution to calculate the bottom-hole pressure of the injection well, and then the typical curve of bottom-hole pressure response is drawn. Typical curves are divided into 5 flow sections: wellbore storage section, transition section, inner radial flow section, outer low seepage flow section and boundary reflection section. Finally, sensitivity analysis of starting pressure gradient and dynamic permeability parameters is carried out, and pressure response of different seepage laws is compared. Taking an injection well in Changqing Oilfield as an example, the well test results show that the permeability around the injection well is larger, and the outer zone is affected by the combination of starting pressure gradient and dynamic permeability, and there is a starting pressure gradient in the outer area, and the permeability is smaller, which is consistent with the field practice. This method is a relatively general numerical pressure calculation method, among which the conventional injection well composite well test analysis method and low permeability reservoir single zone test analysis method are special cases of this method.

Key words: low permeability reservoir, injection wells, starting pressure gradient, dynamic permeability, composite reservoir, well test analysis method