Shale-Gas Experience as an Analog for Potential Wellbore Integrity Issues in CO2 Sequestration
- Los Alamos National Laboratory
Shale-gas development in Pennsylvania since 2003 has resulted in about 19 documented cases of methane migration from the deep subsurface (7,0000) to drinking water aquifers, soils, domestic water wells, and buildings, including one explosion. In all documented cases, the methane leakage was due to inadequate wellbore integrity, possibly aggravated by hydrofracking. The leakage of methane is instructive on the potential for CO{sub 2} leakage from sequestration operations. Although there are important differences between the two systems, both involve migrating, buoyant gas with wells being a primary leakage pathway. The shale-gas experience demonstrates that gas migration from faulty wells can be rapid and can have significant impacts on water quality and human health and safety. Approximately 1.4% of the 2,200 wells drilled into Pennsylvania's Marcellus Formation for shale gas have been implicated in methane leakage. These have resulted in damage to over 30 domestic water supplies and have required significant remediation via well repair and homeowner compensation. The majority of the wellbore integrity problems are a result of over-pressurization of the wells, meaning that high-pressure gas has migrated into an improperly protected wellbore annulus. The pressurized gas leaks from the wellbore into the shallow subsurface, contaminating drinking water or entering structures. The effects are localized to a few thousands of feet to perhaps two-three miles. The degree of mixing between the drinking water and methane is sufficient that significant chemical impacts are created in terms of elevated Fe and Mn and the formation of black precipitates (metal sulfides) as well as effervescing in tap water. Thus it appears likely that leaking CO{sub 2} could also result in deteriorated water quality by a similar mixing process. The problems in Pennsylvania highlight the critical importance of obtaining background data on water quality as well as on problems associated with previous (legacy) oil and gas operations. The great majority of the leakage issues in Pennsylvania are due to improperly abandoned wells, however in the media there is no clear distinction between past and present problems. In any case, significant analytical work is required to attribute differing sources of methane (or CO{sub 2} in the case of sequestration). In Pennsylvania, a relatively lax regulatory environment appears to have contributed to the problem with inadequate oversight of well design and testing to ensure well integrity. New rules were adopted at the end of 2010, and it will be interesting to observe whether methane leakage problems are significantly reduced.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- DOE/LANL
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1011474
- Report Number(s):
- LA-UR-11-10378; TRN: US201109%%450
- Resource Relation:
- Conference: 10th Annual Carbon Capture & Sequestration Conference ; 2011-05-02 - 2011-05-05 ; Pittsburgh, PA, Pennsylvania, United States
- Country of Publication:
- United States
- Language:
- English
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ABANDONED WELLS
AQUIFERS
CARBON
DESIGN
DRINKING WATER
METHANE
REPAIR
SAFETY
SHALE GAS
SOILS
SULFIDES
TESTING
WATER QUALITY
WATER WELLS