Production calculation model considering variable start-up pressure gradient in ultra-low permeability reservoirs

Ultra-low permeability reservoir fluid presents nonlinear flow, pressure sensitive effect, permeability changes, resulting in starting pressure gradient changes. At present, the problem of variable-start pressure gradient and pressure-sensitive effect is not considered in the existing production calculation method. To solve these problems, based on the percolation theory of ultra-low permeability reservoir, this study established the variable-start pressure gradient production calculation model based on the pressure sensitivity effect by using the pressure-sensitive effect formula and other laboratory experiment results. Taking Block C of Chaoyanggou Oilfield as an example, the main influencing factors of development effect under the condition of variable start-up pressure gradient are analyzed. The results show that the start-up pressure gradient leads to a significant decline in oil well production. When the variable start-up pressure gradient and pressure sensitive effect are considered simultaneously, the effective production radius of the oil well decreases, and the production of the oil well varies nonlinearly with the change of pressure. Compared with the calculation results of the non-Darcy seepage production model, the calculation accuracy of the model in this paper is improved by 4.17%.