Task Completed: 2013 – Summer 2016
Much of the public concern about oil and gas drilling and hydraulic fracturing has been focused on the potential for those activities to damage fresh water aquifers. A wellbore with good integrity should assure subsurface fluids (gas, oil, fresh water, or brine) remain isolated from each other throughout all phases of the well life, including after plugging and abandonment.
AWG water quality researchers looked into the causes of water contamination by oil and gas. In Colorado, there have been 45 documented cases where oil and gas migrated into freshwater aquifers. This is .067% of the wells that have been drilled in Colorado. Half of these incidents have been positively linked to a specific wellbore failure. Colorado has no documented cases of wellbore integrity failures that have led to water contamination since new cement requirements were adopted by the state in 2008.
A wellbore consists of several layers of steel casing and cement to ensure that the oil and gas development does not enter ground water. Good wellbore integrity requires the cement to fully adhere to both the steel casing and the borehole. The Oil and Gas Infrastructure Team researched cement adhesion with the goal of offering additional best management practices to the industry to ensure wellbore integrity is maintained in different drilling practices and geologic conditions, and throughout the life of the well.
Above: a figure from Fleckenstein et al. showing that overall improvements have been made in well design. Here, cement casings to isolate hydrocarbons are now built longer (closer to the surface) than ever before.
The Natural Gas Infrastructure team investigated the structural integrity of the steel pipe and cement components of natural gas wells in the subsurface.
- Task 1: Assessment of the isolation of aquifers. Developed a finite element analysis model to assess the downhole effects of in situ conditions, well construction and operations on hydraulic fracturing fluid or borehole gas migration.
- Task 2: Estimation of the probabilities of isolation failure. Classified failure mechanisms, define volumes of possible failures, examine industry and regulator reported failure data, and estimate probabilities of isolation failure.