Overcoming technology challenges in the deepwater Gulf of Mexico is critical to future US energy supply.
The deepwater (especially the ultradeepwater) areas of the Gulf of Mexico offer the greatest near-term potential for significantly adding to US oil and natural gas reserves and production.
The US Minerals Management Service estimates the deep waters of the gulf contain resources totaling about 45 billion bbl of oil and 232 tcf of gas. And the individual prospects are more prolific: According to MMS, in the past 10 years, the average deepwater field added over 67 MMboe of reserves vs. about 5 MMboe for shallow-water fields. The successes are even more substantial as the play has expanded into ever-deeper waters in recent years. Since early 2000, new deepwater drilling added more than 6.2 billion boe of reserves, up 50% from the total deepwater reserves discovered during 1974-99.
That trend is further borne out by the recent extended well test of the Jack discovery by Chevron Corp. with partners Devon Energy Corp. and Statoil ASA, according to Chris Oynes, regional director, Gulf of Mexico region, US Minerals Management Service.
The successful flow test “increased confidence in discovering and producing oil and gas from deep Lower Tertiary formations in the deepwater Gulf of Mexico,” he says. “This announcement and other deepwater successes provide support for a significantly large impact on the country’s reserves.”
The Lower Tertiary trend could be as wide as 300 miles and involve as many as 3,000 blocks, according to MMS. After 12 discoveries, industry estimates put the trend’s potential recoverable resources at 9-15 billion boe. The discoveries, all in more than 5,000 ft of water and with some wells approaching or exceeding 30,000 ft total depth, demonstrate how the deepwater Gulf of Mexico is a technology-driven play.
“To date, 99% of the oil and gas produced from the gulf has come from relatively young rock, down in geologic age to the Miocene,” notes Steven Hadden, senior vice-president, exploration and production, Devon. “Until a few years ago, the industry did not have the technology in place to find or develop resources found in deeper formations in the ultradeep waters of the gulf.”
“These structures have not been clearly imaged due to the presence of salt canopies covering much of the gulf’s Lower Tertiary prospects,” Hadden adds. “As with many of our opportunities, we’ve turned to high technology to unlock this potential.
Technology challenges
Despite the milestone achieved with the Lower Tertiary successes, there remain daunting technology challenges in the deepwater gulf.
Bill Coates, president, Schlumberger North America, says, “Key hurdles when working in deep water are the resolution below salt for seismic and the costs associated with ultradeepwater development due to high reservoir pressures and the need for strong flow assurance programs.”
Among deepwater exploration technology challenges, Coates singles out seismic below 10,000 ft of salt, as well as high-pressure/high-temperature drilling and evaluation. In deepwater drilling, he cites drill string harmonics-shock and vibration in deep, extended-reach wells. The main challenges in deepwater production are flow assurance and premature failure of deepwater completions, Coates says.
Improved seismic needed
Improvements in seismic imaging below the salt canopies of the deepwater gulf are critical, says Newfield Exploration Co. Vice-Pres. Elliott Pew.
“In regards to technology, subsalt imaging is the probably is the single largest improvement that can reduce risk,” he says. “Wide-azimuth towed streamer data show good promise in this area.”
Rick Fowler, vice-predident and general manager, Gulf of Mexico operations, Dominion Exploration & Production, a unit of Dominion Resources Inc., Richmond, VA. elaborated on the seismic challenges in the deepwater gulf: “Most of the high-quality opportunities available are in subsalt horizons, where applying seismic methods can be challenging,” he says. “We can use seismic to identify structures below the salt; however, our seismic images are not yet accurate enough to adequately predict continuity within these structures.”
Fowler notes that once a subsalt discovery is made, it is extremely difficult to adequately appraise the reservoirs, thus requiring many wells to ascertain their size. Not only is such appraisal drilling costly, it delays a development decision.
“If the seismic data could be improved to enable quicker, more accurate appraisals, we could drill fewer wells, better optimize the size and type of facility, and improve cycle time,” Fowler contends. “Accurate seismic depth migrations using proper velocity and salt models are key to improving the images of these structures below salt.”
Drilling challenges
Transocean Inc.’s David Mullen, vice-president, North and South America, cites these drilling challenges in the deepwater gulf:
- “Extreme well depth requires rigs with an improved critical-path load capacity beyond what currently exists with the very high-end fifth-generation [drilling] vessels.
- “The narrow window on the allowable frac and pore pressure gradient complicates well construction to the point that a number of prospects are undrillable with current technology.
- “Extrene pressure encountered in some ultradeep prospects will require a BOP with a pressure rating beyond 15,000 [psi].
- “Technology [is needed] to overcome the problems in running and retrieving riser string in a high-current environment.”
Oynes presses the issues surrounding the difficulties in drilling high-pressure/high-temperature wells in the deepwater gulf.
“Before these wells can be drilled, completed, and produced, materials that can withstand these extreme conditions must be developed,” he notes, citing “drilling fluids with rheologies that will withstand temperatures in excess of 350° F., elastomeric seals and downhole tools with electronics that can withstand elevated temperatures, and blowout preventers that can handle the extreme pressures.”
New completion technologies needed include extra-high-strength tubulars that can withstand partial hydrogen sulfide and carbon dioxide levels that require certification by the National Association of Corrosion Engineers, Oynes points out.
On the production side, Oynes calls for christmas trees made of steels that can sustain high temperature differentials between the outside seawater and the internal fluid temperatures, as well as the corrosive nature of the produced oil and gas.
“Alloys for flowlines and risers subjected to the same elevated pressures, corrosive environment, and differential temperatures will need to be developed as well,” he adds.
Oynes also points to the production technology challenges involved in subsea pumping and processing.
“Both of these issues would increase ultimate recovery of producing properties,” he says. “Multiphase metering on a platform and subsea is also a challenge that has not been completely conquered.”