Two New Seismic Source Technologies Developed For Safer And Less Costly Deep-Ocean Exploration

The INEEL-led research team has developed new seismic source technologies--devices used to create shock waves that travel below the drill bit through the ground. Drillers then record the resulting acoustic data to gain insight into the location of high- and low-pressure areas before they drill. The research team presented results to the National Oil and Gas Technology Partnership on Nov. 17, 2000.

Research team members tested two new technologies--the Regenerative Combustion Source and the Capacitive Discharge Source--in August 2000, at a hydrology research park in Arkansas. Then they compared the results against standard commercially available technologies to see how well the new technologies performed.

The patent-pending Regenerative Combustion Source creates shock waves by supplying hydrogen gas and then sparking it with an electric fuse--creating a controlled explosion in the borehole, well below the ocean floor. The second technology, called a Capacitive Discharge Source, uses an electric spark to create an arc. The result is a steam bubble that bursts, creating a shock wave.

The research team set out to build better seismic sources after a workshop in 1997 sponsored by the Drilling Engineering Association. At the workshop, a group of oil and gas producers, oilfield service companies, research organizations and regulatory agencies found that the biggest technical hurdle to drilling safely in deep water is the inability to accurately sense the pressure levels in marine sediments before drilling.

Current borehole seismic technologies are effective at sending shock waves horizontally through the earth, but not vertically, below the drill bit where drillers really need information. In addition, drillers must take all the drilling equipment out of the borehole before using current seismic sources, a substantial effort considering the miles and miles of pipe involved.

Deep water drilling--drilling in water greater than 400 meters deep--is still a new frontier for oil and gas companies. "Shallow marine shelf drilling is pretty well understood," explains the INEEL's Dave Weinberg, Ph.D., a science and engineering fellow, "but deep water drilling presents a new set of technical challenges that need to be overcome--not dissimilar to putting a man on the moon."

Deep water drilling is a surprisingly delicate procedure, heavily dependent on how much the drilling crew knows about subsurface pressures at the drill site. By drilling into the sea floor, drillers create a well borehole that has lower pressure than the surrounding area. They keep the ocean sediments from collapsing the well by using a slurry of mud that maintains the pressure inside the hole just slightly greater than outside the well. However, if pressure in the mud slurry is less than pressure in the sediments, the subsurface fluids will flow into the well, causing a blowout. Blowouts are extremely dangerous situations for both the personnel on the drilling ship and the environment.

To prevent blowouts, drillers case the well--cementing pipe into the well as a liner. As they drill deeper into the ocean floor where the pressure becomes progressively higher, drillers must use increasingly smaller-diameter casing pipes to compensate for the pressure, creating what looks like an inverted telescope. Casing at deep ocean depths can take days because the cement has to dry before drilling can continue. "When you consider that a drilling rig costs between $150,000 and $200,000 a day, fewer lengths of casing means less pipe and less time. That's money in the bank," said Weinberg.

Therefore, deep water drilling becomes a balancing act of preventing blowouts--a complicated process of anticipating when to case the borehole. Being too conservative and putting in a lot of telescoping casing pipes isn't the answer. "Sometimes drillers literally run out of hole," explains Weinberg. "The diameter of the pipe becomes so small they can't continue, and then can't reach the depths they need." More effective seismic sources can help alleviate this problem of locating overpressured sediments.

Weinberg's research is funded by the DOE's Fossil Energy Program through the Natural Gas and Oil Technology Partnership Program. The purpose of the program is to increase the nation's energy security by boosting domestic gas and oil production and decreasing imports to help meet future national energy needs. The research supports the DOE's energy mission.

"With energy prices getting as much attention as they are today, technology to help the U.S. produce more oil and gas must be a priority," said Barry Short, INEEL's director of Energy Efficiency and Natural Resources.

The research team tested both INEEL technologies at a 3,300-acre site in northeast Arkansas, managed by the University of Arkansas. The site is essentially a hydrology characterization research park, peppered with 30 boreholes that can be used for just this type of technology testing. The site is also already very well mapped, so the INEEL team can easily determine the effectiveness of the two new seismic sources.

"It's like turning a trumpet horn. Seismic energy can be very directional, so if we can't look ahead, we can get some unpleasant surprises," said Weinberg.

The prototype sources tested gave surprisingly good results. The sources allowed researchers to acquire seismic reflection signals of more than 160 feet away, which was better than anticipated. The power sources used were very small compared to those that would be used commercially. "The two sources were less than one one-hundredth as powerful as commercial sources, making the distance sensed even more impressive," said Weinberg.

Before the results become commercially viable, more testing and field hardening of the sources need to be done. INEEL's industrial partners, Chevron and Halliburton, will ultimately decide if the sources are ready for "prime time."

"If they continue to perform as expected, we should see one or the other in use within a few years," said Weinberg.

The team includes researchers from the INEEL, Lawrence Berkeley National Laboratory, Chevron Petroleum Technology Company, Halliburton and the University of Arkansas.

The INEEL is a science-based, applied engineering national laboratory dedicated to supporting the U.S. Department of Energy's missions in environment, energy, science and national defense. The INEEL is operated for the DOE by Bechtel BWXT Idaho, LLC, in partnership with the Inland Northwest Research Alliance.