Oil & Natural Gas Projects
Exploration and Production Technologies
An Ecological Framework to Evaluate Impacts of E&P Releases
This project was funded through DOE's Natural Gas and Oil Technology Partnership
Program. The Partnership Program establishes alliances that combine the resources
and experience of the nation's petroleum industry with the capabilities of the
national laboratories to expedite research, development, and demonstration of
advanced technologies for improved natural gas and oil recovery.
The primary goal of this project was to quantify the effects of habitat removal
and fragmentation on population densities of vertebrates in areas of oil and
brine spills. To facilitate this, the objective was to develop a general framework
within which ecological risk assessments can be conducted at an ecosystem or
eco-region scale. The plan included development of exclusion criteria from the
ecological risk assessment (ERA) process based on the minimum size and spatial
configuration of spills.
Oak Ridge National Laboratory (ORNL)
Oak Ridge, TN
Lawrence Livermore National Laboratory (LLNL)
Tallgrass Prairie Preserve
Osage County, OK
University of Tulsa
Oklahoma State University
The project developed spatially explicit individual-based models (IBMs) for
terrestrial vertebrates. The strength of IBMs is in their ability to simulate
linkages between the physical environment-as modified by human activities (such
as oil production)-and animal populations. ORNL focused on the development of
a population model that used habitat suitability index as the basis for representing
spatial variation in habitat of the American badger, Taxidea taxus. LLNL focused
on the relationship between prairie voles and short-horned owls. The badger
and the owl represent the top predators in the food chain, or trophic level.
Trophic interactions were used to model and define the degree of habitat disturbance
caused by brine spills. The badger model showed a steady increase in population
(away from the immediate spill areas), until the population reached carrying
capacity with annual pulses corresponding to spring births.
Simulation of the impacts of fragmentation caused by different patterns of new
roads and wells on vertebrate populations provided valuable data on the impact
of spills and petroleum development on terrestrial vertebrates. The project
recommendations can be used to provide a useful tool for developing good management
practices for new road and well development during petroleum exploration and
production. The data also provide knowledge on the development of spatial decisions
for locating new wells or restoring spills or old well pads. By providing a
database and a model of impact on terrestrial vertebrates, the project offers
valuable information on well siting, disturbances, and vegetative restoration
to minimize effects on population densities.
A large literature exists on the impacts of habitat disturbance and fragmentation
on vertebrate populations. However, the literature reveals little evidence of
terrestrial wildlife exposure to hydrocarbons at oil and gas E&P sites.
Preliminary evidence suggests there is little uptake of hydrocarbons by plant
species, and that hydrocarbons are avoided by earthworms (a prime food for lower
vertebrates). Most terrestrial vertebrates tend to avoid contaminated sites
and visible E&P activity sites such as well pads. ORNL and LLNL focused
their research on developing a method to study and model species relationships
to habitat disturbances.
The Tallgrass Prairie Preserve is a 15,200 hectare area owned by the Nature
Conservancy in Osage County, OK. There are 600 non-producing and 120 active
oil and gas wells on the preserve. One percent of the area is disturbed by spills,
well pads, and oil-related production facilities. The area covered by brine
spills is less than 0.1% of the preserve. The native vegetation and terrestrial
vertebrate species exist in a mature and healthy grassland community, making
it a prime locality to study the effects of oil and brine spills on population
ERA is a tool used by many regulatory agencies to evaluate the impact to ecological
receptors from changes in environmental conditions. Typical ERAs are toxicologically
based, require complex modeling of transport and exposure, and are very labor-intensive.
The current effort is to streamline the ERA process and to identify ecological
screening criteria for excluding sites from formal risk assessment. By considering
spatial context, it should be possible to develop mitigation and monitoring
efforts to more appropriately address E&P sites within the context of an
The project compared simulated badger population sizes when brine spills are
added to the trophic model. The prairie vole and other small rodents and birds
are the prime prey for both the badger and the short-horned owl. Scenarios studied
the effect of one large brine spill and many small spills of the same size.
The disturbance patterns at E&P sites that may impact terrestrial vertebrates
- Brine spills.
-Bare ground, denuded of vegetation.
-Slow recovery and area of difficult restoration.
- Hydrocarbon spills.
-Biodegradation, enhanced remediation.
-Rapid recovery, given enough nutrients.
-Slower recovery if plants are sprayed.
- Wellheads, well pads.
-Large number of small, isolated disturbed areas.
- Other management disturbances.
-Grazing (bison are the major grazing species on the preserve).
The study found several links from habitat disturbance to population-level
- Individuals unable to find territories may emigrate.
- Movement costs may increase for animals that avoid or do not settle in disturbed
- Forage vegetation or prey may be less available.
- Animals may be unable to find mates or breeding territories.
- Remaining habitat may provide fewer refuges from predators.
The habitat-based model for the badger included assessment of:
- Breeding, mating, post-mating, birthing, rearing offspring, and dispersal
- Daily movement to a 30-meter resolution.
- The need for a flexible approach to variation in life history.
- Territory acquisition and movement.
- Habitat suitability based on vegetation cover, presence of small mammals
(prey), and disturbance history.
- Brine scar disturbances.
-Assumed to be complete, with no benefit to badgers.
-Result in high movement-survival costs.
- Daily chance of survival influenced by age, habitat quality, and movement.
The trophic model for the prairie vole and short-horned owl included:
- Prairie vole IBM.
- Resource evaluation of growth and grazing condition of vegetation.
- Climatic dependence of breeding and vegetation growth.
- Territorial behavior (residents and wanderers, home range)
- Survival based on sufficient food and age constraints.
- Reproduction based on mating, nesting, maturity, and generation time.
- Spatial dispersal due to search for empty nesting location with sufficient
Simulation results determined that:
- Badger populations decrease with increasing spill area, and the probability
of a population crash increases with size of the disturbance area.
- Fragmentation, as measured by the number of spills, increases effects on
- The time to extinction of prairie vole population declines with increasing
spill area, if the ratio of spill area to total area is large enough.
- Vole density is sensitive to the interaction of predation and fragmentation,
with fragmentation causing population extinction in the presence of predation
and stabilizing the population in the absence of predation.
- Species with higher sensitivity to brine and oil spills were found to be
habitat specialists, less-mobile species, and species with a high site fidelity
or edge-sensitive species.
The researchers concluded that:
- The study covered an insufficient number of species, ecosystems, and model
structures to recommend general criteria for excluding E&P sites from
- The declines of population density and time to extinction observed in the
Tallgrass Prairie Preserve were related to the area of disturbance but were
not precipitous enough to be called thresholds.
- The disturbed area of concern may depend on the number of spills.
- Predation can alter the result of fragmentation on a prey species.
The project is complete. This was a joint partnership with LLNL project FEW
Carlsen, T.M., and Efoymson, R.A., 2001, Current directions in screening-level
ecological risk assessments, SPE 68319, SPE/EPA/DOE Exploration and Production
Environmental Conference, San Antonio, TX, pp. 26-28, February 2001.
Project Start: June 12, 2000
Project End: September 30, 2004
Anticipated DOE Contribution: $500,000
Performer Contribution: $500,000 (50% of total)
Other Government Organizations Involved
Lawrence Livermore National Laboratory
NETL - Jesse Garcia (Jesse.Garcia@netl.doe.gov or 918-699-2036)
ORNL - Rebecca Efroymson (EfroymsonRA@ornl.gov or 865-574-7397)
The short-horned owl is the top of the LLNL trophic model, which moves from
vegetation to prairie vole to owl.
The American badger is sensitive to habitat disturbance both in its home range
and in the effect disturbances have on its prey species.
The prairie vole is the most common and best indicator of the rodent population
on the Tallgrass Prairie Preserve.