Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation

Davies, Richard J.; Almond, Sam; Ward, Robert S.; Jackson, Robert B.; Adams, Charlotte; Worrall, Fred; Herringshaw, Liam G.; Gluyas, Jon; Whitehead, Mark

doi:10.1016/j.marpetgeo.2014.03.001

Cited by 347 publications

(205 citation statements)

References 25 publications

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“…In a study of more than 300,000 wells in Alberta, Bachu & Watson [20], have found that approximately 6.5% of the oil and gas wells in the province have lost their integrity, leading to surface casing vent flow or gas migration. Similar or even higher percentages of well failures have been recorded in other producing sedimentary basins around the world [21]. Considering the high number of oil and gas wells drilled in mature sedimentary basins, their density, their failure rate, and the propagation of pressure build-up over large distances in the case of commercial-scale CO2 storage operations, the flow of formation fluids into shallow protected groundwater is certainly possible, suggesting the need for caution, even if the probability is low.…”

Section: Introductionsupporting

confidence: 76%

Arsenic and Selenium in Formation Waters: Environmental Implications for Carbon Dioxide Storage in Geological Media

Hitchon¹,

Bachu²

2017

WIT Transactions on Ecology and the Environment

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In an attempt to mitigate climate warming, CO2 is being stored in geological media, including deep strata in sedimentary basins where formation waters commonly have high salinity. While there are numerous studies of reactions between injected CO2 and formation waters, little attention has been given to problems which might arise in areas affected by the pressure build-up generated by CO2 injection, which may extend for tens to hundreds of kilometres from the injection site. This paper draws on information from the Alberta Basin (Canada), and considers possible contamination consequences should formation water leak into shallow protected groundwater, with particular reference to As and Se. Arsenic and selenium were determined in 300 formation waters from strata 800 m or deeper: i.e., at depths and locations potentially suitable for CO2 storage. Although in about 72% of samples both elements were below detection (0.1 mg L ) and Se (44 mg L -1 ) are far above those reported in other sedimentary basins. Most samples were from drill stem tests, so contamination by As-bearing chemicals was unlikely. The most likely source for both elements is pyrite present in the aquifer, with chloride being the main removal control. More than 20,000 oil and gas wells in Alberta have lost their integrity, resulting in gas migration and surface casing vent-flow, which, if within the area of pressure build-up, could be conduits for contaminating local groundwater. Dilution up to several thousand times would be required to render these waters safe in the groundwater regime -possible, though with a low probability. These results suggest the need for more attention to the effect of pressure build-up and formation water composition in CO2 storage projects.

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Section: Introductionsupporting

confidence: 76%

Arsenic and Selenium in Formation Waters: Environmental Implications for Carbon Dioxide Storage in Geological Media

Hitchon¹,

Bachu²

2017

WIT Transactions on Ecology and the Environment

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“…The 34,392 available depths of these 192,925 wells range from 0 to 8,696 m, with many wells penetrating through different formations. Wellbore integrity issues occur in a wide variety of wells and conditions and have been linked to fluid leakage (45)(46)(47)(48)(49)(50). Some of the existing wells can potentially act as leakage pathways and connect deeper, more saline formations to shallower, fresher groundwater (51,52).…”

Section: Resultsmentioning

confidence: 99%

Salinity of deep groundwater in California: Water quantity, quality, and protection

Kang

Jackson

2016

Proc. Natl. Acad. Sci. U.S.A.

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Deep groundwater aquifers are poorly characterized but could yield important sources of water in California and elsewhere. Deep aquifers have been developed for oil and gas extraction, and this activity has created both valuable data and risks to groundwater quality. Assessing groundwater quantity and quality requires baseline data and a monitoring framework for evaluating impacts. We analyze 938 chemical, geological, and depth data points from 360 oil/gas fields across eight counties in California and depth data from 34,392 oil and gas wells. By expanding previous groundwater volume estimates from depths of 305 m to 3,000 m in California’s Central Valley, an important agricultural region with growing groundwater demands, fresh [<3,000 ppm total dissolved solids (TDS)] groundwater volume is almost tripled to 2,700 km3, most of it found shallower than 1,000 m. The 3,000-m depth zone also provides 3,900 km3 of fresh and saline water, not previously estimated, that can be categorized as underground sources of drinking water (USDWs; <10,000 ppm TDS). Up to 19% and 35% of oil/gas activities have occurred directly in freshwater zones and USDWs, respectively, in the eight counties. Deeper activities, such as wastewater injection, may also pose a potential threat to groundwater, especially USDWs. Our findings indicate that California’s Central Valley alone has close to three times the volume of fresh groundwater and four times the volume of USDWs than previous estimates suggest. Therefore, efforts to monitor and protect deeper, saline groundwater resources are needed in California and beyond.

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“…One of the most common pathways is along the wellbore [e.g., Dusseault et al, 2000;Jackson et al, 2013;Vidic et al, 2013;CCA, 2014;Davies et al, 2014]. Well integrity to prevent leaks of gas and other fluids to groundwater or to ground surface is a cornerstone of environmental protection in all oil and gas drilling operations.…”

Section: Water Resources Researchmentioning

confidence: 99%

“…Elsewhere, the Norwegian Petroleum Safety Authority (PSA) has reported that 15% of 323 production wells, and 33% of 83 injection wells drilled between 1970 and 2006 on the Norwegian Continental Shelf (NCS) had some kind of well integrity problem (related to tubing, annulus safety valves, casing or cement), while 7% of these wells had to be shut-in (closed) due to well integrity issues [Vignes and Aadnøy, 2010]. In a more recent investigation, Davies et al [2014] reported that 6.3% of 8030 wells drilled between 1958 and 2013 in the Marcellus shale of Pennsylvania in the northeast United States showed well integrity and barrier failure and 1.3% of these wells were leaking to surface. These results, among others reported in the literature for other countries (see Davies et al [2014] for a complete review) highlight the impact of well construction on the migration of fluids to groundwater and to ground surface.…”

Section: Water Resources Researchmentioning

confidence: 99%

“…In a more recent investigation, Davies et al [2014] reported that 6.3% of 8030 wells drilled between 1958 and 2013 in the Marcellus shale of Pennsylvania in the northeast United States showed well integrity and barrier failure and 1.3% of these wells were leaking to surface. These results, among others reported in the literature for other countries (see Davies et al [2014] for a complete review) highlight the impact of well construction on the migration of fluids to groundwater and to ground surface.…”

Section: Water Resources Researchmentioning

confidence: 99%

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Numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well

Nowamooz

Lemieux

Molson

et al. 2015

Water Resources Research

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Methane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with a multiphase flow and multicomponent numerical model. The conceptual model used for the simulations assumes that the target shale formation is 200 m thick, overlain by a 750 m thick caprock, which is in turn overlain by a 50 m thick surficial sand aquifer, the 1000 m geological sequence being intersected by a fully penetrating borehole. This succession of geological units is representative of the region targeted for shale gas exploration in the St. Lawrence Lowlands (Qu ebec, Canada). The simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer. The leakage of fluids can subsequently lead to the contamination of groundwater resources and/or, in the case of methane migration to ground surface, to an increase in greenhouse gas emissions. The minimum reported surface casing vent flow (measured at ground level) for shale gas wells in Quebec (0.01 m 3 /d) is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration. The simulations suggest that an adequately cemented borehole (with a casing annulus permeability k c 1 mD) can prevent methane and brine leakage over a time scale of up to 100 years. However, a poorly cemented borehole (k c ! 10 mD) could yield methane leakage rates at the base of an aquifer ranging from 0.04 m 3 /d to more than 100 m 3 /d, depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation. These values are compatible with surface casing vent flows reported for shale gas wells in the St. Lawrence Lowlands (Quebec, Canada). The simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years, depending on cementation quality and hydrodynamic properties of the casing annulus. Simulated longterm brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10 25 m 3 /d (10 mL/d) to 10 23 m 3 /d (1 L/d). Based on scoping calculations with a well-mixed aquifer model, these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration in a pristine aquifer to 1 mg/L, which is significantly below the commonly recommended aesthetic objective of 250 mg/L for chloride.

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Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation

Cited by 347 publications

References 25 publications

Arsenic and Selenium in Formation Waters: Environmental Implications for Carbon Dioxide Storage in Geological Media

Arsenic and Selenium in Formation Waters: Environmental Implications for Carbon Dioxide Storage in Geological Media

Salinity of deep groundwater in California: Water quantity, quality, and protection

Numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well

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