An Assessment of the Probability of Subsurface Contamination of Aquifers from Oil and Gas Wells in the Wattenberg Field, Modified for Water Well Location

Abstract

The United States National Science Foundation has funded a Sustainability Research Network (SRN) focused on natural gas development in the Rocky Mountain region of the United States. The objective of this specific study is the assessment of the use of existing water wells to monitor the risk of the contamination by the migration of fracturing fluids or hydrocarbons to fresh water aquifers. An additional objective of the study is to modify existing risk estimates using the spacial relationships between the existing water wells and producing oil wells. This will allow estimates of single barrier failure and multiple barrier failure resulting in contamination to be projected for oil and gas wells in areas without surrounding water wells to detect migration, based on well construction type. Since 1970, the Wattenberg Field in Colorado has a large number of oil and gas wells drilled. These wells are interspaced tightly with agricultural and urban development from the nearby Denver Metropolitan area. This provides a setting with numerous water wells that have been drilled within this area of active petroleum development. Data from 17,948 wells drilled was collected and analyzed in the Wattenberg field, allowing wells to be classified by construction type and analyzed for barrier failure and source of aquifer contamination. The assessment confirms that while natural gas migration has occurred in poorly constructed wellbores is infrequent, it can happen and that the migration risk is determined by the well construction standards. The assessment also confirms that there has been no occurrence of hydraulic fracturing fluid contamination of fresh water aquifers through wellbores. The assessment determines both the spacial proximity of oil and gas wells and surface casing depth to water wells to determine the utility of water wells to monitor migration in oil wells.

Methane Leakage From Hydrocarbon Wellbores into Overlying Groundwater: Numerical Investigation of the Multiphase Flow Processes Governing Migration

“…Unconventional wells may leak more often than conventional wells due to structural integrity failure of cement and/or casing barriers intended to separate production fluids and groundwater, which are usually much longer and experience higher pressures (e.g., Ingraffea et al, 2014). However, some evidence suggests that modern regulations decrease the likelihood of leakage from any new well (Stone et al, 2016). Increased annular pressure may not lead to incidents of groundwater contamination, especially in newer hydrocarbon wells (Lackey et al, 2017;Sherwood et al, 2016;Watson & Bachu, 2009).…”

“…Regulations vary by state, but most require similar protection to minimize the risk of groundwater contamination. Oil‐and‐gas operators have the option to cement more of the annular space, which has become increasingly common through time in the Wattenberg Field (Stone et al, ).…”

“…The lowest was just over ambient pressure at the depth of leakage and the highest corresponded to the maximum pressure for which casings commonly used in the Wattenberg Field are rated (Schlumberger, ). The range of pressures simulated here could realistically be encountered in annular spaces in the Wattenberg Field via failures of cemented surface casings, cemented production casings, or annular hydrostatic pressure (e.g., Stone et al, ). To define pressure at the source zone, an “extra” cell was added to the model.…”

Development of Self-Healing Cement Slurry through the Incorporation of Dual-Encapsulated Polyacrylamide for the Prevention of Water Ingress in Oil Well

“…The crack generation in the cement sheath causes the migration of the formation fluids through the micro-fractures, thereby resulting in sustained casing pressure [ 5 , 6 , 7 ]. Upon crack development, the formation fluid starts migrating through the cement sheath into the well-bore, resulting in excessive water production or sometimes causes contamination of aquifers [ 8 , 9 ]. Therefore, the service life of the cementing can be increased either through crack-repairing by squeeze-cementing or application of self-healing cement.…”