A THEORETICAL STUDY ON ROCK BREAKDOWN PRESSURE CALCULATION EQUATIONS OF FRACTURING PROCESS

Based on the dual effective stress concept of porous media formation, the calculation method for rock breakdown pressure is studied in the paper, and a new composite calculating formula is provided. It is possible to predict breakdown pressure for different types of rocks if different parameters are used in the formula. The application scope of currently used equations is analyzed by using of new formula. The H-W equation can only be used to calculate the breakdown pressure of non-permeable rock; therefore it gives the upper limited value of breakdown pressure. The H-F equation can be used to calculate the breakdown pressure of high permeability rock, therefore, it gives the lower limited value of breakdown pressure. It is available to predict the breakdown pressure of any kinds of rocks by the new calculation formula. It consists of previous two calculation equations, and totally combines the calculation of non-permeable rock and that of permeable rock in one.