Numerical simulation and parametric analysis for designing High Energy Gas Fracturing

This paper presents a new comprehensive approach to model High Energy Gas Fracturing (HEGF) process. This coupled model consists of 6 sub-quantitative modules, including (1) loading build-up due to propellant deflagration, (2) gas-liquid interface displacement caused by killing liquid column movement, (3) stress distribution around the casing wellbore and the perforation holes, (4) fluid penetration through the perforation holes, (5) rate dependent critical pressure of fracture initiation and (6) hydro-mechanical coupled fracture propagation. The solution to the coupled model is obtained combining the analytical method and finite difference method, which solves the mass conservation equation and energy conservation equation with the subsystem pressure and temperature as the main variables. Subsequently, The single pulse and the mull-pulse HEGF processes are simulated. The dynamic changes of the loading built-up of propellant deflagration, the movement of killing liquid column as well as the dynamic propagation of fracture are further studied. Meanwhile, in-depth analysis has been applied on the affect sensitivity of the five key parameters to the single pulse HEGF results as well as the mechanism of multi-pulse HEGF. The results indicate that the final lengths of fractures generated by single pulse HEGF can be extended with the increase of the perforation density, the diameter of perforation holes, the thickness of propellant column and the total propellant quality. However, the effect of the height of killing liquid column is insignificant. It also demonstrates that the mull-pulse HEGF could bring multiplier fractures length by concatenating series propellants with different burning rates. This coupled model could add new dimensions to the understanding of the coupled mechanism of single pulse and multi-pulse HEGF. In addition, the model could be applied as a parameters quantitative design tool to assist the field implementation of these technologies.