Interpretation of hydraulic fracturing pressure-time records using interactive analysis methods

Abstract The accuracy of hydraulic fracturing stress measurements depends strongly on an accurate interpretation of the fluid pressures recorded during the tests. However, a variety of factors can lead to indistinct instantaneous shut-in or fracture reopening pressures which contributes to uncertainties in the data interpretation. A complex hydrofrac data set from a 1.5 km deep wellbore at Moodus, Connecticut is used here to discuss an interactive system for analysis of pressure, injection rate and accumulated volume as well as the pressurization rate and stiffness of the hydraulic system at various stages of the experiment. The hydraulic fracturing data presented here require a particularly careful inspection of the pressure records because the tests at Moodus were conducted in a seismically active reverse faulting environment. In such a stress regime (when the least principal stress is vertical) induced vertical fractures at the borehole wall will tend to “roll over” and propagate horizontally. Ideally the complete stress tensor can be derived from such a test but it is necessary to clearly separate the shut-in pressure values of the different propagation stages.