An Improved Modeling of Solid Propellant Fracturing to Produce Long Fractures in Wellbore Formations

Simultaneous ignition of an entire exposed surface required for accurate modeling of solid propellant fracturing process is difficult to achieve because wellbore fluids decrease flame spread rate and negatively impact burn propagation, and can extinguish portions of the burning propellant grain thereby resulting in slower pressure loading rates and insufficient energy for producing long fractures. A proposed system is that in which the propellant is protected from wellbore fluids by housing it in a vessel with a means for creating openings to allow combustion gases produced to flow into the wellbore. On this basis, a model was developed using mass and energy conservation laws, and applying a concept of choked flow in the openings to relate conditions in the wellbore to the vessel. The results of the peak pressure and pressure rise time obtained from the model for multiple-fracture regime agree well with the reported experimental results and thus establishing the validity of the model in predicting the wellbore pressure during solid propellant fracturing system. A star-shape burning surface is proposed for the propellant and calculations carried out proves it to be more effective as it provides more energy for producing long fractures essential for more flow of oil and gas from the reservoir into the wellbore than a conventional circular surface of the same burning area. The exterior angle of star-shape burning surface was found to be a function of the number of vertices of the star and it determines the progressive burning nature of the propellant.