Searching for the Optimal Well Spacing in the Eagle Ford Shale: A Practical Tool-Kit
Douglas Portis¹, Gervasio Barzola¹, Mark Murray¹, and Hector Bello¹
¹Pioneer Natural Resources
Four years after the "discovery" of the Eagle Ford shale play, most operators have shifted their efforts from appraisal and delineation, to full-field development. This commonly involves drilling multiple (three to four) horizontal wells, simultaneously from one common surface location (or pad). Inter-well spacing ranges from 330 – 1000 feet across the trend as industry searches for the optimum well spacing for a range Eagle Ford shale thickness, rock-quality, pressure and thermal maturity windows. Pioneer Natural Resources (PXD) has followed this same transition and routinely drills three well pads with approximate 500 foot spacing between wells, which are completed with "zipper-frac" treatments. This paper presents a tool-kit designed in-house and currently employed to monitor well interference, communication and pad performance/drainage efficiency. The ultimate goal of this project is to better understand the reservoir response during hydraulic fracture treatments (at 500 ft spacing) and use these learnings to positively impact the full field development and future.
A multidisciplinary team including drillers, geologists, reservoir engineers, and completions engineers has designed an integrated data acquisition "tool-kit" to address the above issues. Integral to the tool-kit are chemical and radioactive tracers, pumped during the stimulation of one or more wells in a given pad. These data help our interpretation of fracture generation, fracture growth and fluid flow/ proppant placement (i.e. proppant distances, fluid distances, and fracture geometry). The chemical tracers provide (a) insight into distances frac fluids travel in the subsurface and (b) deliver an estimate of production variability along the well-bore, providing a pseudo-production log. The radioactive tracers aid in interpretation of geometry and architecture of fractures developed during stimulation. The data from the several microseismic surveys also assists in the recognition, quantification and distribution of stimulated rock volume.
A major portion of this tool-kit includes the monitoring of pressure communication in offset wells during fracture stimulation and flow-back/production. Pressures observed in offset wells during completion and subsequent flowback and production are overlaid with fracture treating pressures which allow for the identification of individual completion stage responses. Pressure interference tests were designed to occur post stabilized flow by shutting in all wells in a pad and then turning on a single well while monitoring the pressure in the remaining wells. Subsequent interference tests over a period of several months allow for a better understanding of the changes in fracture conductivity and effectively propped fractures.
AAPG Search and Discovery Article #90202 © AAPG/STGS Geoscience Technology Workshop, Eagle Ford plus Adjacent Plays and Extensions Workshop, February 24-26, 2014, San Antonio, Texas