Oil & Natural Gas Projects
Exploration and Production Technologies
Risk Reduction and Soil Ecosystem Restoration in an Active Oil Producing
Area in an Ecologically Sensitive Setting
This project is funded through Oil and Gas Environmental program solicitation
DE-PS26-01NT41048. The program addresses the need for reducing compliance costs
and improving environmental performance by providing lower-cost compliance technologies,
providing a sound scientific basis for cost-effective, risk-based regulatory
decisions, and improving access to public lands and sensitive environments by
demonstrating environmentally protective technologies.
The goals of this project are to develop a probability risk management tool
for the petroleum industry that can be used to identify oil field areas that
have high potential for accidental oil and brine spills. A second goal is to
provide guidance on performing ecological risk assessments for oil and brine
contaminated sites by defining appropriate endpoints for remediation and developing
appropriate indicators for these endpoints.
University of Tulsa
The work in this project resulted in the development of a probability risk assessment
tool that can be used to minimize the environmental impact of oil field equipment
failure. A second product of the research was the development of practical and
cost-effective strategies for managing accidental oil and brine spills.
The risk assessment tool developed in this project can be used by environmental
managers to minimize the environmental impact of equipment failure by identifying
the equipment most likely to cause oil and brine releases. The assessment and
modeling tools developed in this project can mitigate financial liability and
environmental impact through resource allocation that will reduce the severity
of ecosystem damage caused by accidental petroleum or brine releases.
The results of this work contribute to the development of practical, appropriate,
cost-effective, and technically-defensible strategies for management of accidental
spills of produced fluids. Nematode numbers and community structure have been
identified as an appropriate ecological indicator which is both sensitive, low-cost,
and widely available.
Over 25 papers and presentations have resulted from this project and have been
widely distributed within the industry and regulatory communities. The methods
developed in this project are technically and ecologically sound and easily
taught to small independent producers. The results of this research are being
used by the Integrated Petroleum Environmental Consortium (IPEC) as the basis
of numerous workshops for small producers, remediation guidelines and training
videos, and field analysis kits which IPEC distributes free of charge.
Much of the infrastructure of the domestic petroleum industry is aging and requires
maintenance. This situation puts the industry at a high risk of equipment failures
resulting in environmental damage. Industry resources for environmental protection
are limited and it is important to both the domestic petroleum industry and
regulators that the protection of the environment be as cost-effective as possible.
Non compliance is often associated with accidental releases and not with intentional
abuse or neglect. In this context, probabilistic risk assessment (PRA) provides
a consistent, logical, and scientifically defensible approach to risk minimization
in E&P operations by quantifying the likelihood of certain outcomes and
identifying the events that lead to these outcomes. With this tool limited resources
can be allocated to areas of high risk thus minimizing the risk of environmental
damage and benefiting the domestic petroleum industry, the regulating agency,
and the public.
Once a spill of produced fluids has taken place it must be remediated or "cleaned"
in order to restore the economic and/or aesthetic value of the impacted land
as well as preventing further contamination of soil, groundwater, and surface
waters. But how clean is clean? One view is that the soil ecosystem is "clean"
when the ecosystem is sufficiently restored to support its previous use or an
acceptable alternate use. However, there is currently a shortage of information
on the ecological risks associated with oil and brine spills. A lack of information
on the ecological risk of oil and brine spills can lead to overly conservative
and unnecessarily costly eco-based regulations.
This project has two related areas of focus: (1) development of a probability
risk assessment tool for oilfield oil and brine spills, and (2) the study of
the effects of oil and brine contamination on grasslands soil ecology and the
development of cost-effective remediation methods for oil and brine release
Risk Assessment. The Probability Risk Assessment (PRA) tool was developed
to estimate the probability that a spill resulting from equipment failures will
occur within a certain time horizon.
Development of the tool was conducted using data and specific examples from
the protected Tallgrass Prairie Preserve (TGPP) in Osage County, Oklahoma. The
TGPP contains various leases that include over 100 wells with average production
of 1.5 to 2 bbl/day of crude oil and 15-20 bbl/day of brine per well.
A data base compiled by the Oklahoma Corporation Commission (OCC) with state-wide
oil and brine spill information and interviews with operators was used to identify
the primary causes and frequency of oil and brine releases from equipment failures.
Causes of oil and brine releases identified include: corrosion and plugging
of pipe; corrosion and outlet plugging of storage tanks; corrosion and outlet
plugging of oil/water separators; plugging, shaft misalignment, and loss of
lubrication in pumps.
Analysis of equipment failures provided the probability that a piece of equipment
will fail over a given time span. Other analysis indicated how the size and
transport distance of the releases impact potable water, economic loss, and
The result of the analyses and modeling is a Risk Index Map showing the areas
of the oil field that have greater than normal risks for oil and brine spills.
A Risk Index Map is generated by combining the probability of a failure with
the financial loss produced. This Probability Risk Assessment tool can be used
by operators to monitor the areas of greatest risk and identify areas most in
need of repairs and equipment replacements.
Remediation. The second focus of this project was the study of the effects
of oil and brine contamination on grasslands soil ecology and the development
of remediation methods. The results of this work provide guidance for performing
ecological risk assessments for oil and brine contaminated sites by helping
to define appropriate endpoints for remediation and developing appropriate indicators
for these endpoints. This part of the project was also conducted on spill sites
in the TGPP. The tallgrass prairie ecosystem is more sensitive to the impacts
of produced fluids than soil ecosystems in most oil-producing areas and allows
subtle responses of ecological indicators to be discerned.
Two brine and oil spill sites were studied. The spills had killed the vegetation
in the vicinity and lowered concentrations of soil microbes. In one area the
brine had migrated downgradient and contaminated a farm pond. Detailed comparisons
were made between the spill sites and closely adjacent portions of the native
tallgrass prairie ecosystem.
Biodiversity was recorded in a number of groups of organisms including plants,
bacteria, and soil fauna. Comparisons were made between the number of different
species to calculate species richness and diversity indices. Indicators of system
upset such as low Nitrogen, Phosphorus, and biomass levels were also examined.
After trials of various remediation methods the best method found was a two-step
process. The first step involved tilling prairie hay and fertilizer into the
affected soil to enhance leaching of the soil and provide soil organic matter
that helped to build soil structure and sustain the soil ecosystem. The second
step involved installing a subsurface drainage system to intercept brine components,
enhance the lateral subsurface transport process, and prevent further contamination
of the farm pond. Success of the methods was indicated by reductions in chloride
concentrations in the soil by 93% and sodium concentrations by an average of
78% within 4 years.
Approximately 95% of the site revegetated and microbial community structures
approached those of the unimpacted control as salt was leached out of the site.
Nematode numbers and community structure were identified as sensitive and inexpensive
indicators of the status of restoration of damaged soil ecosystems.
The hay and fertilizer remediation methodology can be easily and inexpensively
implemented by small independent oil and gas producers without hiring outside
contractors. With access to a tractor and tiller and a local source of hay,
an independent producer can remediate a spill site for about $200 per acre.
The interception trench could also be constructed by the operator but the cost
would depend on the topography of the site.
Current Status (June 2005)
The research has been completed. The final report is being prepared.
T.M. Harris, Tapp, J.B., Sublette, K.L. Remediation of Oil-Field Brine-Impacted
Soil Using a Subsurface Drainage System and Hay, Environmental Geosciences,
V.12, No.2 (June 2005)
K.L. Sublette, Moralwar, A., Ford, L., Duncan, K., Thoma, G., Brokaw, J. Remediation
of a Spill of Crude Oil and Brine without Gypsum, Environmental Geosciences,
V.12, No. 2 (June 2005)
J. Berton Fisher and K.L. Sublette Environmental Releases from Exploration and
Production Operations in Oklahoma: Type, Volume, Causes, and Prevention, Environmental
Geosciences, V.12 No.2 (June 2005)
Sublette K.L., Kolhatkar, R., Pim, K. Long-term Impacts of a Crude Oil Spill
on a Pristine Soil Ecosystem, Proceedings of the 25th Arctic and Marine Oil
Spill Program Technical Seminar, Calgary, Alberta, Volume 2, 979-1011 (2002)
Nebel-Almedia, Cherie Comparison of Remediation Methods at Three Sites Contaminated
with Crude Oil and Brine in the Tallgrass Prairie Preserve, M.S. Thesis, University
of Tulsa (2001)
Duncan, K., Kolhatkar, R., Subramanian, G., Narasimhan, R., Jennings, E., Microbial
Dynamics of Oil-Impacted Prairie Soil, Applied Biochemistry and Biotechnology,
77-79, 421-434 (1999).
Project Start: January 25, 2001
Project End: June 30, 2005
Anticipated DOE Contribution: $776,392
Performer Contribution: $292,028 (27% of total)
NETL - John Ford (email@example.com or 918-699-2061)
University of Tulsa - Kerry Sublette (firstname.lastname@example.org or 918-631-3085)
Site J6N brine scar in the Tallgrass Prairie Preserve, summer 1999.
Site J6N brine scar after remediation in May 2004. Bare spots are buffalo wallows.