Exploration and Production Technologies
Advanced Fracturing Technology for Tight Gas: An East Texas Field Demonstration

DE-FC26-01NT41326

Goal:
To improve the performance and reduce the cost of fracture treatments.

Background:
Many operators today are using simple water frac treatments to stimulate production from tight sand formations. Water is preferred because it is generally cheaper than gel-based treatments. Most fracture simulation models however, were not designed for simple water frac treatment. This project used multiple geomechanical and petrophysical methods to analyze data from fracture treatments from the tight gas sands in the Bossier Sand play in East Texas. This information was used to update current gel-based models to better predict proppant transport, fluid leakoff, and fracture cleanup and performance of water frac processes. The improved model was then used to develop guidelines for selection of fracturing fluids and optimization of the future fracture field tests. These fracture field tests were applied to the Cotton Valley Sands, a section very similar to the Bossier Sands, in Carthage Field.

Performers:
University of Texas at Austin 
Anadarko Petroleum Corp.

Location:
Austin, Texas 78713
Field work conducted on Anadarko Petroleum Corp. leases in:
Dowdy Ranch Field, Freestone County, Texas
Carthage Field, Panola County, Texas

Project Impact:
The computer modeling software developed by this project improves fracture stimulation design by better analysis of proppant transport, fluid leakoff, turbulence within the frac fluid and viscosity of the frac fluid. It is applicable for frac fluids ranging in viscosity from water to gels. This software can be used in any formation where fracture stimulation is deemed useful. Application of this software will provide a better estimate of the results of a particular frac design, thus reducing materials and equipment use and therefore reducing costs.

Accomplishments:

  • Six wells in the Dowdy Ranch field were chosen as data wells. The data collected on these wells included a complete set of logs including dipole sonic logs, downhole temperature and pressure data during frac jobs on six frac jobs. In addition pressure buildups were run on two wells. Tracer logs with multiple isotopes were run on two wells. The fracture treatments included breakdown and mini-frac stages. Production logs were also run on five of the wells.
  • Data set collected on the APC Anderson # 2 well represents the most comprehensive data set ever collected for a commercial gas well and provides an invaluable data set for analysis. A full suite of logs was run across the zones of interest. The entire interval was cored and a complete set of core analysis is available across the sands. This core data is posted on Omni Laboratories, Inc. web site: www.omnilabs.com (under Log In: User ID = DOE, Password = UT). A petrophysical study of this data was conducted as a Master Thesis. Stress profiles derived from dipole sonic logs across the pay zone and in the shales below were calibrated with stress tests conducted. Downhole pressure and temperature data were collected during the two frac jobs conducted on the Bonner and York sands.
  • Proppant transport clearly is a central issue in all of these wells. Experiments were conducted to study the effects of fracture walls, fluid rheology and high flow rates on proppant settling and retardation. The experimental data allowed us to develop correlations for proppant settling that can be used in conjunction with theoretical models to better describe the complex physics of proppant settling and convection in fractures. These correlations have been incorporated in an updated version of the frac software developed by the University of Texas at Austin and now known as UTFRAC-3D.
  • Subsequently, this acquired knowledge was applied to two wells in Carthage Field, Panola County, Texas. The Cotton Valley Sand section here is essentially identical in overall characteristics to that of the Bossier Sands in Dowdy Ranch Field on the other side of the East Texas Basin. After frac flow rates for the CGU 26-18 and CGU 26-19 were 950 MCFD and 2,000 MCFD respectively. Reservoir pressure was 44% of original pressure in 1970 when Cotton Valley Sand production was established and unit size has been reduced from 320 acres to 20 acre spacing. It was found during this work that CO2 foam fracs provided the best results.

Production data from Carthage Field, Panola County, Texas

Current Status and Remaining Tasks: : 
This project is completed.

Project Start Date: October 1, 2001 
Project End Date: December 31, 2004

DOE Contribution: $ 883,931
Performer Contribution: $ 419,326

Contact Information: 
NETL – Tim Grant (412-386-5457 or tim.grant@netl.doe.gov)
University of Texas at Austin – Mukul Sharma (512-471-3257 or msharma@mail.utexas.edu)

Additional Information:

Final Project Report [PDF-3.57MB]

Technology Assessment  - Prepared by Mukul M. Sharma, University of Texas at Austin & Richard Sullivan, Anadarko Petroleum Corporation

Sharma, M.M., Gadde, P.B., Copeland, D., Sigal, R., Fielder, R. and Sullivan, R., 2003, The Impact of Proppant Placement on the Productivity of Tight Gas Wells, Gas TIPS, p. 19-24, Fall 2003.

Pertinent Publications:
Mahadevan, J. and Sharma, M.M., 2003, Clean-up of Water Blocks in Low Permeability Formations, SPE 84216.

Parekh, B. and Sharma, M.M., 2004, Clean-up of Water Blocks in Depleted Low-Permeability Reservoirs, SPE 89837.

Gadde, P.G., Liu, Y., Norman, J., Bonnecaze, R. and Sharma, M.M., 2004, Modeling Proppant Settling in Water-Fracs, SPE 89875.

Sharma, M.M. and Gadde, P.B., 2004, Slick Water and Hybrid Fracs in the Bossier: Some Lessons Learned, SPE 89876


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