Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Lowering Drilling Cost, Improving Operational Safety, and Reducing Environmental Impact through Zonal Isolation Improvement for Horizontal Wells Drilled in the Marcellus and Haynesville Shales
CSI Technologies, LLC, Houston, TX
University of Houston Chemical Engineering Department
Effective zonal isolation is crucial to optimized completion and production of wells drilled into shale gas reservoirs. This project will specifically focus on the Marcellus and Haynesville shale. These wells consist of long horizontal sections that are cased and cemented prior to creating a number of fractures along the lateral. These wells present challenging conditions for cementing. Typically the equivalent circulation density (ECD) range between well control and lost circulation is narrow increasing the potential for gas flow through the cemented annulus. With improper cementing, annular pressure at the surface results in safety and operational issues throughout the life of a well.
Current industry practices in drilling and completing these wells have often failed to provide adequate zonal isolation. The economics of shale gas production dictate minimizing cost, rapid well drilling and completion, and a “production line” approach to the drilling programs. This driver has lessened application of technology to individual shale well cementing and pushed a “one-size-fits-all” approach. The independent producers currently dominating shale production would normally rely on service companies to provide engineering and technical support to solve this tough problem. However, excessive workloads and deeply discounted pricing equate to a bare-bones, basic approach without much attention to engineering details. Since the independent producers lack large technical staff or laboratory facilities, the limitation of individual resources has stifled efforts to improve cementing performance.
The outcomes of incomplete zone isolation discussed above demand that the extra time, money, and effort required to develop methods to seal the complete annulus be invested. A recent swell of public concern over safety and protection of potable water reservoirs from damage due to fracturing treatments performed on Marcellus Shale wells has intensified concerns over achieving adequate zonal isolation. Migration of gas or other pollutants through an inadequately sealed annulus to fresh water formations or the surface poses an environmental and safety threat.
CSI, Chesapeake, and the University of Houston Chemical Engineering Department propose to undertake a comprehensive study of the cementing process applied in the Marcellus and Haynesville Shale fields and to develop an integrated process to optimize zonal isolation, reduce job problems, minimize remedial cementing requirements, and reduce rig time spent waiting on cement. The approach to this study includes understanding fundamentals and underlying causes of each cementing issue, engineering and laboratory evaluations of how to mitigate the issues, operational improvements required to implement optimized cementing protocols, simple methods to assess the level of cementing sophistication required to achieve zonal isolation, and performance measurements to confirm improved function or outcomes.
The zonal isolation problems encountered in the Marcellus and Haynesville Shale fields are similar to those observed in other major shale gas operations in the U. S. Results from this study will be easily transferrable to these other operations regardless of whether the completions utilize a cemented or uncemented production string. At some point in the well above the production zone, a complete annular seal must be applied to control and isolate well fluids from potable water reservoirs and the Earth’s surface.
Key deliverables associated with the process will be:
- Fundamental understanding of current cementing practices in the Marcellus and Haynesville Shales, the level of zonal isolation success, and issues resulting from incomplete zonal isolation.
- New cementing protocols designed to eliminate issues and a simple observation technique to quantify degree of difficulty associated with cementing a particular casing.
- Quantitative measurement of zonal isolation improvement resulting from new cementing protocols.
- Assessment of the effects of improved zonal isolation in mitigating environmental impact of shale well drilling and completion.
Potential impacts from the project will be:
- Lower cost of well construction.
- Fewer operational problems such as gas migration.
- Less remedial cementing required over the well’s productive life.
- Lessened risk of affecting potable water reservoirs by migrating fluids from the shale reservoirs.
- Transfer of these results to the industry and all stakeholders.
Reduction in problem during primary cementing operations in the Haynesville shale is focused on two areas. First, there are gas migration issues in the upper hole section that manifests as annular pressure after cementing. This gas migration is estimated to occur on 10% of the wells. The second issue involves incomplete displacement of the cement or premature stopping of the cementing treatment prior to bumping the plug. This occurs about 15% of the time. Each of the above issues translates into about $100,000 of remedial cost for the well. For the life of the Haynesville Shale field (3500 wells) this problem would amount to over $44 million. Similar problems exist in the Marcellus shale however the gas migration issue is far and away the most dominant primary cementing issue. All operators have begun installing a recently-mandated intermediate casing for Marcellus wells to alleviate potential safety due to the gas migration issue as well as environmental problems due to the potential of the gas entering the ground water zones. The cost of this intermediate string is about $750,000/well drilled. If this string could be safely eliminated in future wells a cost savings of over $4.5 billion could be achieved for the expected life of the field. In addition just eliminating the current gas migration issue on 10% of the wells would amount to an additional cost savings of $60 million.
Phase 1 of the project will be classified as the Research and Ddevelopment portion of the project while Phase 2 will be the demonstration portion of the project.
Principal Investigator: Jeff Watters
Doe Share: $3,006,000
Recipient Share: $2,500,000
Project Duration: 2 years