P-wave seismic time-lapse analysis of horizontal well completions causing pressure compartmentalization

Abstract

When horizontal wells are completed many changes can occur. During completions, pressure changes take place because of the fluid and proppant injected. One way of monitoring such changes is through the use of time-lapse seismic data. In Wattenberg Field, located near Greeley, Colorado, Anadarko Petroleum Corporation (APC) has teamed up with the Colorado School of Mines Reservoir Characterization Project (RCP) to acquire time-lapse seismic data over a section of land in which eleven horizontal wells were completed. The P-wave seismic is of considerable interest since the P-waves are sensitive to pressure changes in the reservoir. However, the first step is to determine if there are considerable pressure changes associated with the completions. The net pressures from the completion reports per stage were studied. The net pressure indicates the creation of hydraulic fractures and the propagation of those fractures. This thesis hypothesizes that where there is a positive net pressure, the pressure is building up near the wellbore and a negative net pressure indicates hydraulic fracture propagation. A pre-stack seismic inversion was done to determine the P-impedance changes in the time-lapse surveys. The percent difference in P-impedance volume was observed with the net pressure trend in corresponding reservoir intervals. This analysis showed that the negative changes in P-impedance correlate with the negative net pressure. This analysis implies that the formation is being hydraulically fractured and the fractures are propagating away from the wellbore, so the net pressure is decreasing resulting in the decrease in P-impedance. The results of this study allows for integration between the completion parameters and the time-lapse seismic analysis. This study then provides insight for the stimulated reservoir volume, since the seismic anomalies in combination with the completion pressures can identify areas that were fractured better than others. These areas correspond to negative net pressures during hydraulic fracturing stimulation.