Pioneer Natural Resources in the Texas unconventional shale plays continues to utilize various microseismic technologies to better understand stress and pressure relationships that occur during hydraulic stimulation. Company-wide we have been primarily utilizing seismic monitoring equipment placed in the well bore, and to a lesser extent surface systems, to capture stimulation fracture geometries. These data are used to obtain a better understanding of the stress heterogeneity within the reservoir and completion as well as to optimize the well spacing. Over the past year we have monitored over 30 wellbores in Texas.
In one study area, utilizing microseismic data as a proxy for pressure we have observed differences in fracture height, overlap of stages, magnitudes of events, number of events, as well as azimuthal changes within the microseismic data for various zones within our lower Permian age reservoirs. Pioneer has recently collected over twelve microseismic jobs (386 stages) using predominately one downhole acquisition system that allows for inter-comparisons of data in Reagan and Upton Co. Texas. We have minimized changes with the acquisition of the data, and the stimulation pumping parameters, so that we can track how changes to completion design are manifested in the rock. In some cases, our landing zones between wells have been modified so that we can assess the specific stress heterogeneity related to the geomechanical properties of different layers within the main pay zones. This broad foundation of data allows the individual to recognize differences within the stimulation as they relate to the geology or completion.
Our datasets demonstrate the geometry of the pressure field as imaged with the microseismic data is variable and appears to be controlled by a number of factors including the local geology, completion practices, previous stimulations and adjacent production. Pioneer has mapped in detail the density of the microseismic event field, and noted variations in the height, length and widths of the hydraulic stimulation as well as the development of the pressure field away from the perforations. We have used the data to better understand well spacing and placement as well as define potential vertical fracture barriers for the Wolfcamp Formation. The knowledge gained from microseismic investigations, combined with reservoir models, have economic importance to the company as it plans future development of a shale oil play. Spacing decisions directly impact well count and capital deployed by the firm to maximize development of reserves.