Exploration and Production Technologies

Stimulation Technology for Deep Well Completions

DE-FC26-02NT41663

Goal: 
The goal is to reduce uncertainty and increase success in frontier and emerging deep formation gas plays, by evaluating the current state-of-the-art in stimulation technology for deep and/or high temperature formations via: 1) a comprehensive literature review and industry interviews, 2) evaluating rock mechanics issues, 3) studying fracture growth behavior in deep formation completions, and 4) performing three to five small case studies evaluating stimulation in key deep formations.

Background:
The U.S. Department of Energy’s (DOE) Deep Trek Program is targeted to improving the economics of drilling and completing deep (>16,000 feet) and/or high temperature (>350EF) and high pressure (>10,000psi) (HTHP) natural gas wells in the U.S. This effort is focused on the second objective of the Deep Trek program – improved Economics in Deep Well Completions. The objective of the work is to review current and past stimulation activity and research results for deep and/or HTHP well completions and stimulations in the United States. The information will develop and extend the knowledge base for the U.S. DOE and industry in the U.S. and Gulf of Mexico (GOM). The results will help reduce uncertainty and increase success in frontier and emerging deep and HTHP formation plays in the U.S. and GOM. The project shall provide the U.S. DOE and U.S. gas industry with an assessment of:1) what is currently working in deep and HTHP formation stimulation and completion technology, 2) what is currently not working in deep and HTHP formation stimulation and completion technology, and 3) what needs improvement in deep and HTHP formation stimulation and completion technology.

The initial phase of the project consisted of assessing deep gas well drilling activity (over the 1995-2007 time period) and performing a region-by-region industry survey of deep gas well stimulation practices. Of the 29,000 oil, gas, and dry holes drilled in 2002, about 300 were drilled in the “deep” well depth and/or temperature range. Of these, 25 percent were dry, 50 percent were HTHP completions and 25 percent were simply deep completions. South Texas had about 30 percent of these wells, Oklahoma 20 percent, Gulf of Mexico Shelf 15 percent and the Gulf Coast about 15 percent. The Rockies represent only two percent of deep drilling. Of the 60 operators who drill deep and HTHP wells, the top 20 drill almost 80 percent of the wells. Six operators drill half the U.S. deep wells. Deep drilling peaked at 425 wells in 1998 and fell to 250 in 1999. Drilling is expected to rise through 2004, after which drilling should cycle down as overall drilling declines.

Performers:
Pinnacle Technologies Inc. – Project management and all research products
Gas Technology Institute Information Center – Literature search assistance
Spears and Associates (SAI) – Industry survey assistance
IHS Energy Group (HIS) – Database purchase

Location:
San Francisco, California 94103
Houston, Texas 77090

Project Impact:
Deep resources represent approximately 158 tcf (at depths greater than 15,000 feet), and are one of the sources of natural gas that will play an important role in meeting the growing need for natural gas in the United States. The Energy Information Agency estimated seven percent of U.S gas production came from deep formations in 1999. This contribution is expected to increase to 14% by 2010. Much of this deep gas production will come from the Rocky Mountain, Gulf Coast, and GOM sedimentary basins. The challenges of drilling and completing deep high temperature and high pressure wells are significant. Rock mechanics are not well understood at deep, high pressures. This project is to help provide some of that understanding.

Results:

  • Performed searches of multiple databases for information on deep wells and deep well stimulation and sifted forty relevant papers from an initial set of over 750 publications;
  • Evaluated deep drilling records from commercial database, identified activity level by region, formation and operator from 1995-2002, and forecast activity to 2007;
  • Conducted a study to determine current basic well completion/stimulation practices, successes, failures, and technology issues via in-depth interviews with 50 engineers and managers;
  • Based on the literature search and survey results, prepared an evaluation of rock mechanics issues and fracture growth behavior in deep formations;
  • Prepared case studies of stimulations in deep gas formations identified from the literature search and survey, focusing on the integration of fracture modeling and production data analyses to better understand fracture performance; and
  • Delivered workshops, technical papers/articles, and a comprehensive final report.
The evaluation of rock mechanics issues related to stimulation of deep wells yielded a number of recommendations, including:
  • Optimization of stimulation designs for HPHT wells requires good data collection (stress, modulus, reservoir pressure, and permeability);
  • While an understanding of the stress regime can be obtained from geological general trends, local stress in a reservoir may deviate from the regional trend and the most reliable stress measurements can be made with microfracs;
  • Sometimes, fracture containment must be measured with independent diagnostics, like micro-seismic or tiltmeter mapping, because lithology may control fracture containment rather than stress; and
  • Proper net pressure evaluation can only be made from bottom-hole measurements, and proper datafrac procedures are required to extract the closure pressure.

The case studies developed for this project included an analysis of three deep gas productive targets in the Table Rock Field near Sweetwater, Wyoming (a higher permeability dolomite layer flanked by thick, low permeability sandstones at Lower Weber and Upper Weber) at a depth of roughly 17,300 to 18,100 feet.

Complex hydraulic fractures will pose great challenges for treatment execution and economic well performance in deep HPHT reservoirs.

Current Status and Remaining Tasks:
The last workshop was held in Norman, Oklahoma on February, 23, 2005. The final report is available on request.

Project Start: September 27, 2002
Project End: June 30, 2005

DOE Contribution: $199,000
Performer Contribution: $49,750

Contact Information:
NETL – Gary Covatch (gary.covatch@netl.doe.gov or 304-285-4589)
Pinnacle Technologies Inc. – Stephen Wolhart (steve.wolhart@pinntech.com or 281-876-4564 x 413)

Additional Information:
Final Report Part 1 - December, 2005 - Report split into two parts to facilitate downloads

Final Report Part 2 - December, 2005

Pertinent Publications:
Wolhart, Steve; Rogers, John and Spears, Richard; "Deep Gas Drilling in the United States," Hart's, Drilling, March 2004

Rogers, John D., Lambert, Stephen L. and Wolhart, Steve; "Deep Drilling and Completion Technologies and Challenges," GasTIPS, Spring 2004

Mayerhofer, Michael, StephenL. Wolhart and John D. Rogers; “Results of U.S. Department of Energy Deep Gas Well Stimulation Study,” paper SPE 95639 presented at 2005 SPE annual Technical conference and Exhibition, Dallas, 9-12 October 2005.

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