The Wellbore Integrity pillar focuses on all aspects of well development, from construction through abandonment. There are three high-level goals of this pillar: 1) The adaptation or development of well construction and completion technologies and techniques that assures wellbore integrity and prevents breaches in zonal isolation; 2) providing cost effective fit-for-purpose drilling and completion tools that enable the goals of the other pillars within SubTER; and 3) enabling these advances in extreme downhole environments. Understanding and maintaining wellbore integrity, as well as developing advanced methods to access the subsurface, are fundamental requirements and enabling and essential capabilities to achieving the broader goals of the Subsurface Crosscut.
Research in the Wellbore Integrity and Drilling Technologies Pillar is associated with six different topics, called elements, including:
- Improved Well Construction Materials and Techniques
- Autonomous Completion for Wellbore Integrity Monitoring
- New Diagnostics for Wellbore Leakage
- Remediation Tools and Technologies
- Fit-for-Purpose Drilling and Completion Tools
- HT/HP Well Construction and Completion Technologies
Improved Well Construction Materials and Techniques: The high-level ten-year goal of this element is to discover, develop and deploy novel cements, cement-like materials, sealants, casing materials, fluids, and deployment schemes that improve long-term wellbore integrity.
Development of novel and enhanced engineered materials is crucial to creating more robust and reliable wellbore systems. Critical materials research problems include enhanced casing, durable and flexible cement, improved centralizers, lost-circulation mitigation materials, and better-performing drilling fluids. In current practice, cemented steel casing is a passive component of the well system. There is potential to make the casing system an active probe of the subsurface environment where the casing system integrates sensors to monitor a suite of parameters (e.g., hydraulic containment, casing stress, corrosion, etc.). Additionally, there is a need to develop casing/cementing systems that are tailored to the target application and subsurface system using materials and processes appropriate for the application. While expandable casing has seen increasing use in the Oil and Gas (O&G) sector, there exists the need to continue advancement of “cementless” casing systems to increase wellbore performance and to reduce costs. New casing systems that provide superior performance at costs appropriate for the application are needed, including next-generation casing/cement systems that self-heal in response to mechanical or chemical damage and are more durable in aggressive chemical environments and at high temperatures. Casing centralization methods that do not impede installation but enhance cementing processes should be developed. Bonding of cement to casing and rock can be enhanced through improved drilling technologies (e.g., drilling “gun barrel” holes) or new methods of annulus cleaning or chemical pre-treatment of the system.
Autonomous Completion for Wellbore Integrity Monitoring: The ten-year goal for this effort is to enable wellbore completions able to autonomously identify isolation and reliability issues over decadal time scales.
There is a paucity of autonomous “health-of-system” downhole monitoring options available today following the construction phase of a well. These sensing systems are needed across a wide spectrum of applications and across timeframes not considered today. For example, the ability to monitor and transmit parameters such as hydraulic containment, casing stress, corrosion, rock/cement/casing bond, and other system performance parameters are not available but are of great interest in all borehole applications.
New Diagnostics for Wellbore Leakage: For systems not integrated into well completions, the ten-year goal for this element is to develop technologies and interpretation methods that produce data that can be directly related to wellbore integrity and zonal isolation issues with high confidence (e.g., logging tools and potential surface-based measurements).
Robust logging systems, fit for the purpose of the well, are needed to diagnose the precise location and character of well integrity problems. These tools could utilize specific physical signals or could involve the development of analytical techniques based on more general tools that allow reliable diagnostics of the integrity of the wellbore. These diagnostics would facilitate accurate targeting of remediation efforts and the selection of the appropriate remediation methodology. Despite commercially available wireline deployable logging and monitoring tools, the ability to confidently diagnose the integrity of a given wellbore with minimal ambiguity is limited. Opportunities exist to develop improved technologies and techniques for diagnosing near-wellbore conditions and interpretation methods. Additionally, the development of surface-based wellbore leakage diagnostics systems would mitigate the costs and effort associated with the deployment of wellbore-based tools.
Remediation Tools and Technologies: The ten-year goal for this element is to develop remediation tools that can selectively repair compromised well regions, including implementation of “self-healing” or externally activated cements and completions, without the use of a drilling or workover rig.
There will always be the need to remediate wells where the integrity of the well has been compromised. Today’s remediation tools rely on placing patches over the unintended breaches in the casing system or purposefully breaching the casing/cement sheath and injecting materials into the offending region. We need remediation tools that selectively perforate and inject materials tailored for the particular geologic region or tools that are nonintrusive and perhaps activate a built-in healing capacity of the well system.
Fit-for-Purpose Drilling and Completion Tools: The ten-year goal for this element is to develop or implement economical fit-for-purpose wellbore construction methods across a wide range of applications (e.g., producing wells, disposal wells, monitoring wells, etc.). This includes the development, implementation, or adaptation of completion methods that control subsurface pressures and fluid flows with high spatial delineation within vertical and horizontal wells.
Drilling and completion technologies are well advanced in O&G and other sectors, but not wholly applicable to the various needs of the U.S. DOE programs. While a thorough examination of available technologies must be compared against program needs, there are significant opportunities to improve performance and costs of program-related drilling and completion technologies. The U.S. DOE programs and industry require a wide range of well types, and adapting, modifying or developing targeted drilling technologies and processes for specific applications is necessary to enable the range of well types envisioned (e.g., wells for seismic monitoring of enhanced geothermal development efforts). Well completions that incorporate “smart” technologies (e.g., zonal isolation, valves, sensors) for applications ranging from geothermal development to environmental restoration are required, including completion technologies that allow manipulation of subsurface permeability and stress. Next generation logging-while-drilling and measurement-while-drilling systems are needed; examples include systems that provide enhanced seismic and electromagnetic imaging and geosteering relevant to the application (e.g., salinity, temperature, etc.). Concepts regarding the development of multilateral systems to provide greater subsurface access with minimal surface infrastructure should be examined. More efficient hole advancement methods, fit-for-purpose drilling fluids, and advancements in downhole telemetry systems will benefit all well construction applications.
HT/HP Well Construction and Completion Technologies: The ten-year goal for this element is to develop high temperature and high pressure HT/HP versions (> 250°C/1500 bar) of the other pillar elements that are available for use as needed.
The lack of HT/HP components, materials and associated downhole tools limits the ability to construct, monitoring and remediate wells in extreme environments. The needs range from component level development, tool assembly materials (elastomers, circuit boards, solders, etc.) to integrated systems that can provide monitoring and remediation tools available at less extreme conditions.