Determination of instantaneous shut-in pressures in hydraulic fracturing tectonic stress measurements

A new method is presented for the determination of the instantaneous shut-in pressures in the hydraulic fracturing tectonic stress measurements. The method is developed by the analysis of the closure process of the crack induced by hydraulic fracturing and it utilizes the inverse of the decrease rate of the downhole water pressure after the shut-in. The plot of the inverse of the decrease rate vs the downhole pressure consists of two straight lines and the instantaneous shut-in pressure can be cleary determined as the pressure of the point of intersection of the two straight lines. The new method is applied to the pressure vs time records which were obtained in field experiments. It is revealed by the application to the field data that the new method can clearly determine the instantaneous shut-in pressures from all of the pressure vs time records applied. (author)