What's new in exploration

	Vol. 225 No. 1
PERRY A. FISCHER, EDITOR

Methane hydrate research results. Gas hydrates, those naturally occurring, ice-like molecular “cages” of natural gas and water, have been widely touted as having the potential to be a resource many times greater than all existing gas and oil resources worldwide. Or perhaps it's not a resource at all. For more than 50 years, various governments have been funding research to study this odd form of methane.

Although commercial/ dry-hole rates are, of course, unknown, its pres-sure/ depth relationship is understood, and it appears that we have learned how to explore for it using seismic (bottom simulating reflectors, amplitude contrasts) and chemical methods.

Although much progress has been made, at the current rate, one has to wonder whether methane hydrates will ever become much more than a never-ending government research project, let alone a bona fide resource. Perhaps it's just the culture of government research projects, or maybe it's because of a subliminal belief that hydrates will never amount to much. But Japan, which has virtually no oil and gas resources, is keen to develop alternate energy resources. It has been leading a consortium of oil companies and governmental agencies on a 16-year project to determine hydrates' status as a resource by 2010.

In 1998, a well was drilled in the northwest Canadian Arctic as part of a gas hydrate research program. In the first quarter of 2002, an expanded consortium undertook The Mallik 2002 Gas Hydrate Production Research Well Program that included the drilling of a vertical 3,800-ft deep main production well and two observation wells, each about 160-ft away. Full-scale field experiments monitored the physical response of the gas hydrate deposits to depressurization and thermal production stimulation. The $14-million project involved a multi-disciplinary science team of some 100 scientists worldwide. This program was the first modern production test of natural gas hydrates.

The two observation wells allowed cross-hole tomography experiments before, during and after several production tests. An extensive suite of open-hole logs and advanced gas hydrate logging tools were run. Continuous wireline core was recovered through the hydrate intervals. The consortium comprised various governmental agencies from Japan, Germany, Canada, India and the US. Japan Petroleum Exploration Co. Canada acted as operator, while the Geological Survey of Canada coordinated the science program.

Hydrates now have an increased potential to become a bona fide resource, according to long-awaited data, released in December at the symposium, From Mallik to the Future, held in Chiba City, Japan. The data come from the Mallik 2002 Program. Of the three most common ways proposed to produce hydrates, depressurization is by far the simplest method to convert hydrates into gas and water. Injecting heat into the formation in the form of hot water or steam is another, and injection of chemicals such as methanol is the third.

Drill site location, named after Imperial Oil's Mallik lease on the Beaufort Sea.

Due to logistics and cost constraints, rather than carry out long-term production testing, the partners decided to conduct carefully controlled production experiments. The response of gas hydrates to heating and depressurization was evaluated, with careful attention to accurately measure both input conditions and reservoir responses. The overall goal was to combine the science and production programs to allow calibration and refinement of reservoir-simulation models capable of predicting long-term reservoir response.

Results from three short-duration depressurization experiments showed that gas can be produced exclusively by this method from gas hydrates with different concentrations and characteristics. “The data supports the interpretation that gas hydrates are much more permeable and conducive to flow from pressure stimulation than previously thought.” In one test, gas production was substantially enhanced by artificially fracturing the reservoir.

The thermal heating experiment comprised five days of circulating hot water within a 56-ft-thick section of highly concentrated hydrate-bearing strata. Gas was continuously produced throughout the test at varying rates, with the maximum flowrate reaching 53,000 cfd. The total gas flowed was small, in part because the test was a controlled production experiment rather than a long-duration well test. A decrease in production at 52 hours into the test was interpreted as a “formation event.”

In addition, the Mallik data showed that gas hydrate deposits contain natural fractures, and that they may be fractured artificially. Several lines of evidence suggested that natural and enhanced fractures may have been conduits for gas transmission from reservoir storage away from the well. Other findings were that, among the possible production techniques, depressurization will produce more gas than heating the formation, while the combination of simultaneous heating and depressuring will produce the greatest amount of gas. The experiments proved the technical feasibility of producing gas hydrates, but economic viability is still unanswered.

Gas hydrates are extremely variable, occurring in deepwater margins worldwide and in permafrost regions on land; they are found in sand, gravel, mud and even on the seafloor in some cases. The deposit at Mallik is particularly rich, so success in that environment does not necessarily translate into other dissimilar areas. Eventually, hydrates' role as a resource – if it exists at all – will be thoroughly characterized; but do not be surprised if research continues at a snail's pace by small groups, funded by governments, over decades. Still, since their potential is so great, even a modicum of success should spur some excitement.