Blog: Updates from the Gulf of Mexico Drilling and Coring Expedition

From 9 May 2017, scientists will sample methane hydrates in the Gulf of Mexico, assessing the origin and evolution of geologic systems that generate and sustain high concentrations of gas hydrate within coarse-grained sediments. DCO scientist and blogger Tiannong "Skyler" Dong will share updates here throughout the expedition. Please check back regularly for news.

23 May 2017: Coming to An End

By Tiannong “Skyler” Dong, University of Texas at Austin, USA

Gulf of Mexico – It is almost time to say goodbye to the Helix Q4000 vessel. We acquired a total of 12 pressure cores at the second drilling site. These pressurized methane hydrate samples are being transported under high pressure and low temperature to Port Fourshon, Louisana by container ship.

The pressure cores will stay at Port Fourshon for about a week to be processed, including being CT-scanned. Most pressure cores will be cut and transferred into approximately 20 four-foot-long pressurized chambers. These chambers will be transported to the University of Texas at Austin for long-term storage. Since the maximum storage capacity is 20 four-foot-long pressurized samples, the rest of the pressurized cores will be depressurized into conventional cores and transported to the Ohio State University in Columbus, Ohio.

All good things must come to an end. Tomorrow morning, the entire science party will fly off the Helix Q4000 vessel by helicopter.

However, this departure does not mark the end of the science. Instead, it is the start of many exciting and elaborate research discoveries.

 

A crane on the Q4000 vessel lifts the refrigerated container that stores pressurized methane hydrate samples and places it onto a container ship. The samples will be transported to Port Fourshon, Louisana for further analyses and processing. 

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19 May 2017: Big Turnaround

By Tiannong “Skyler” Dong, University of Texas at Austin, USA

At the first drilling site, we took a total of eight cores, but only one of them remained pressurized during retrieval. We then drilled a second borehole, 40 feet from the first drilling site.

Things are going much better at the second borehole, a big turnaround for PCTB success! We have collected eight cores, and all of them maintained pressure. On average, each core recovers nine feet of methane-hydrate-bearing sediments out of a ten-foot-long coring chamber, yielding a recovery rate over 90%.

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13 May 2017: First Pressure Core

By Tiannong “Skyler” Dong, University of Texas at Austin, USA

It has been a rough day for the team.

We made five coring attempts, however, only one core made it to the surface under high pressure. All the other cores lost pressure because the ball valve did not seal up the coring chamber effectively.

The only pressurized core recovered 4.6 feet of methane-hydrate-bearing sediments. The unpressurized cores are still valuable, and we can use them for isotope analysis and microbiological studies.

At the moment, the team is actively troubleshooting the PCTB before deploying another coring action. Fingers crossed.

After an unpressurized core was brought up to the surface, scientists and Geotek engineers examine the core and cut it into smaller sections for sampling. 

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12 May 2017: Challenges with Pressure Coring

By Tiannong “Skyler” Dong, University of Texas at Austin, USA

9 a.m. marks a milestone for the Genesis of Methane Hydrate in Coarse-Grained Systems: Northern Gulf of Mexico Slope (GOM2) project. The drilling bits penetrated 6,667 feet of water and 1,343 feet of sediment below the seafloor at Green Canyon Block 955 in the Gulf of Mexico.

Below this depth, a special coring tool, called a Pressure Coring Tool with Ball Valve (PCTB), is deployed to sample methane-hydrate-bearing samples and brought back to the surface under pressure. Essentially, the PCTB is a pressure container that maintains methane hydrate in its solid form.

Methane hydrate is a solid, composed of methane molecules “trapped” inside water ice. The solid is only stable under a range of high pressure and low temperature conditions. When the solid is exposed to conditions outside this thermodynamic stability zone it quickly dissociates into methane and water fluids.

Therefore, the essence of pressure coring is to contain the methane-hydrate-bearing sediments under high pressure while pulling the core back to the surface. If conventional coring tools were used, the methane hydrate would quickly dissociate, melting into water and methane gas before reaching the surface.

There are a lot of engineering challenges associated with pressure coring. It is increasingly challenging as the size of the pressure container gets larger. It is also more challenging to maintain higher pressures. The PCTB tool has a diameter of 2 inches and a length of 10 feet. In order to preserve the methane hydrate, the PCTB has to maintain about 250 atmospheres of pressure.

Operating the PCTB is also challenging. When it is lowered to core the sediments, the engineers and scientists are more than 8,000 feet away from it. After coring the sediments, the PCTB has a self-contained mechanism to seal the coring chamber. As soon as the PCTB is pulled up from the bottom of the bore hole, a built-in spring shuts a ball valve to the seal up the chamber.

Pressure coring in action. The Pressure Coring Tool with Ball Valve (PCTB) being pulled up to the surface.  

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9 May 2017: Sampling Fire Ice in the northern Gulf of Mexico

By Tiannong “Skyler” Dong, University of Texas at Austin, USA

In the early afternoon, the roar of helicopter rotor blades brought the last portion of the science party to the Helix Q4000 vessel floating on 6667 feet of water in the northern Gulf of Mexico. This scientists are part of a team working on the Gulf of Mexico Drilling and Coring Expedition, led by Professor Peter Flemings at the University of Texas at Austin, USA. It is part of the six-year, U.S. Department of Energy-funded project Genesis of Methane Hydrate in Coarse-Grained Systems: Northern Gulf of Mexico Slope (GOM2) initiative.

A major goal of the expedition is to sample natural methane hydrate, commonly known as “fire ice,” which at our location sits 1,358 feet below seafloor beneath 6,667 feet (2,032m) of water. Pressurized samples will be transported to the Pressure Core Center at the University of Texas at Austin.

The name “fire ice” comes from methane hydrate’s water-ice-looking crystals, with methane trapped in an ice-like lattice. Maintaining pressure and temperature during sampling and transportation is crucial. Under Earth’s surface conditions, methane hydrates melt into water and methane gas.

Estimates of global methane hydrate abundance suggest there are 3 trillion metric tons of carbon trapped in methane hydrates, representing a major carbon reservoir in the shallow crust. Methane hydrates are commonly found at continental margins and under permafrost regions.

Over the next two weeks, the science party, along with the geoscience-engineering firm Geotek Coring and the Helix operational crew, will drill two boreholes and sample methane hydrates.  

The aft view portside of Helix Q4000 vessel under maintenance in Brownsville, Texas, prior to the GOM2 expedition.
 
The helicopter taking off from the helideck on the Helix Q4000 vessel after dropping off passengers in the Gulf of Mexico (Photo courtesy of Tom Pettigrew).

Further Reading

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