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Advances in Multisensor Arrays To Monitor Oil and Gas Releases

By Dr. Chris Martens • Richard Butler

The UNC HANDI AADI Seaguard platform is cradled under the recovery spool of a lander.
The Gulf of Mexico oil spill that occurred in April 2010 is considered the largest accidental marine oil spill in the history of the petroleum industry. The spill flowed unabated for three months and caused extensive damage to marine and wildlife habitats and to the gulf's fishing and tourism industries. By July 2011, approximately 491 miles of coastline in Louisiana, Mississippi, Alabama and Florida remained contaminated by the oil.

In light of this spill in the northern Gulf of Mexico and its detrimental effects to the environment, marine scientists are under increasing pressure to develop technology that will enable accurate and reliable detection of light hydrocarbons and oxygen depletion associated with oil spills and gas releases. This research is vital to monitor the long-term effects of water contamination and its threat to coral reef and other coastal ecosystems.

Scientists and engineers in the Department of Marine Sciences at the University of North Carolina at Chapel Hill (UNC) and at Bergen, Norway-based Aanderaa Data Instruments (AADI) have collaborated to develop, test and deploy two new multisensor arrays designed to detect light hydrocarbons and oxygen depletions associated with oil and gas releases. As a beta product evaluator, UNC receives advanced access to AADI products and provides the company with testing and application advice.

The multisensor arrays are built on AADI's Seaguard multiparameter logger platform, which offers configuration flexibility and real-time underwater observation capabilities. These arrays can operate in either a water column survey mode from a submersible, ROV or rosette sampler, or as a deployed observatory in a site-monitoring mode as part of a dedicated benthic array.

Monitoring Hydrocarbons
The first array, called Hydrate-ANDI, or HANDI, by the UNC scientists, was deployed for testing in early July 2010 at Conch Reef off Key Largo in the Florida Keys. HANDI was designed to detect oxygen depletions and any potential oil and gas transport that could threaten marine ecosystems, biodiversity and fish stocks.

The instrument is equipped with two fast-response optodes, a multisensor string of up to 20 smart sensors and additional inputs for four commercially available analog sensors. For example, light hydrocarbon (methane) sensors can be plugged into the system, making the self-contained instrument into a large-scale distributed sensor network or array. Systems can be configured to offer measurements of currents, CTD, dissolved oxygen, salinity and turbidity. The system enabled the UNC team to detect oxygen depletions and potential oil and gas transport along the reef ecosystem's border with the fast-moving water in the Florida Straits.

Following this implementation, the instrument was redeployed as part of a benthic lander oxygen and hydrocarbon monitoring system in the northern Gulf of Mexico. This deployment formed part of a long-term gas hydrate monitoring program, the Gas Hydrates Research Consortium, at Mississippi Canyon Block 118 (MC-118), located within 20 miles of the Macondo well blowout. To continue this article please click here.

Dr. Chris Martens, professor of marine sciences at the University of North Carolina at Chapel Hill, was awarded a Ph.D. in chemical oceanography from Florida State University and a National Science Foundation postdoctoral fellowship at Yale University. He has led numerous surface ship, submersible and Aquarius saturation dive missions, following research interests in sensor technologies for deep-sea and coastal time-series studies.

Richard Butler, group manager at Aanderaa Data Instruments, is a graduate of Massachusetts Maritime Academy where he earned a bachelor's in marine engineering and a U.S. Coast Guard Third Engineer License before retiring as Lt. Cmdr. of the U.S. Navy Reserve. He also served for six years on the board of directors for the Marine Technology Society.

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