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Summary of Publication - Searching for the Optimal Well Spacing in the Eagle Ford Shale: A Practical Toolkit

Mon, 12 Jan 2015

Summary of publication: URTeC 1581750, "Searching for the Optimal Well Spacing in the Eagle Ford Shale:  A Practical Tool-kit" 

Authors:  Douglas H. Portis, Hector Bello, Mark Murray, Gervasio Barzola, Paul Clarke, Katy Canan

South Texas Asset Team, Pioneer Natural Resources, Irving, TX, United States

A multidisciplinary technical team has designed an integrated data acquisition “tool kit” to address the ultimate goal of the project which 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 achieve an optimum well spacing.

Essential 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 the interpretation of fracture generation, fracture growth and fluid flow/proppant placement (i.e proppant distances, fluid distances, and fracture geometry). Several MICRO SEISMIC surveys also assist 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 flowback/production. Subsequent interference tests over a period of several months allow for a better understanding of the changes in fracture conductivity and effectively propped fractures.

Collectively, these data are helping REFINE our GEOLOGIC MODEL and CONFIRMING the significance of attributes extracted from our 3D seismic data set.

Two of the main questions for understanding what spacing this field should be developed on are

  1. What does the induced fracture geometry look like? And
  2. What are the fracture height and half lengths?

For example, given an equal spacing between two sets of three wells on a pad short and laterally extensive induced fractures produce will potentially lead to overlapping and greater connectivity between well bores, conversely, tall and narrowly extensive induced fractures can potentially lead to undrained areas of the reservoir. Further complicating the issue of the former is the understanding of how much communication or connectivity positively impacts well performance and how long do these induced fracture networks remain conductive as we draw down the pressure over time from production. The answers to these questions provide the keys to better understanding how this field should be developed.

Pressure Monitoring

The final tool in the well spacing tool-kit is pressure monitoring. There are a minimum of three applications of pressure monitoring; offset fracture monitoring, interference testing, and initial reservoir pressures.

Offset fracture monitoring is simply placing a pressure monitor on a well offsetting a well or set of wells to record any pressure response of the stimulation. Using the first derivative of the pressure on the offset well and matching the times with the stimulated wells allows observing any pressure response in the offset. Pressure monitoring for interference testing is done on a three well pad where pressure monitors are placed on all three wells, the wells are then shut in to build up pressure, then one of the wells is opened while recording the pressures on all three wells. The concept here is that if the three wells are in communication with each other, then opening one well would allow for the pressure to drop on the remaining shut in wells.

Conclusions

This tool-kit is adding value not only to our understanding of pad well communication, but is aiding in bettering our understanding of well-spacing for the Eagle Ford shale. What we have learned to date is that in general the radioactive tracers are showing proppant transportation at least 500’ and a maximum of 1100’. These data are also used to highlight preferred fracture orientation, which generally conforms to the stress regime observed and interpreted from seismic, bore hole image and sonic logs. Chemical tracers confirm we are moving fluid through this reservoir over 1500’ and the majority of the pad wells stimulated with zipper fracs are generally in communication early on during production and communication can continue for several months. Pressure monitoring has yielded that there is pressure communication during stimulation and production of wells. That pressure communication has decreased over time and we interpret that to represent a reduction in effective induced fracture conductivity over time.

Portis, Douglas H., Hector Bello, Mark Murray, Gervasio Barzola, Paula Clarke, and Katy Canan. "Searching for the Optimal Well Spacing in the Eagle Ford Shale: A Practical Toolkit." AAPG Datapages. URTec, 1 Jan. 2013. Web. 1 Jan. 2015.



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