Simulation on the dynamic variation of downhole gas pressure during deflagration fracturing in screen completed well

Abstract

Deflagration fracturing technique also named high energy gas fracturing (HEGF) technique was applied for creating several radial fractures nearby the wellbore to improve the conductivity. Because of the good applicability for different reservoirs, deflagration fracturing technique was also tried in a screen completed well. However, the theoretical literatures about deflagration fracturing were mainly focused on the open-hole completed or perforated well. A simulation on the dynamic variation of gas pressure in screen completed well was required to avoid destroying the tool because of the structural difference between the screen pipe and casing tube. A model describing the deflagration fracturing process in screen completed well was built. Except for the traditional equations for a perforated well, an equation for the propellant burning, that for the displacement of pressurized liquid column with downhole pipe string operating, and that for the fluid flow through the screen pipe was introduced. Then, a numerical simulation was carried out to validate. Compared with the real production-increasing ratio, the simulated accuracy approached 90%. The calculated maximum pressure was 50.3 MPa when a simulation was done with the given parameters, in accordance with the safety command of screen completed well. The maximum gas pressure had decreased with the increase of hole density and size of the screen pipe. A suggestion for operating pipe during deflagration fracturing was given. Operation with a downhole pipe string of large size and large wall thickness was beneficial for the safety during fracturing process.