August 2008
Energy Tribune
(Posted August 23, 2008)
During the recent World Petroleum Congress in Madrid, Roberto F. Aguilera presented compelling research (conducted with his father, Roberto Aguilera, along with Thomas Harding and Federico Krause, all of the University of Calgary) about the potential endowment of tight gas deposits around the world.

In this case, tight gas is defined as methane found in rocks with permeabilities lower than 0.1 millidarcy. Aguilera’s modeling provides estimates that tight gas deposits may equal known conventional gas resources. Thus, there could be an additional 15,100 trillion cubic feet of natural gas waiting to be tapped – given, of course, the development of new technologies that can facilitate access to it.

Aguilera is a program officer for the Global Energy Assessment project at the International Institute for Applied Systems Analysis (I.I.A.S.A.) near Vienna. He was recently a postdoctoral fellow and an associate instructor at Chile’s Pontificia Catholic University. He holds a B.C. from the University of Calgary and M.S. and Ph.D. degrees in energy economics from the Colorado School of Mines. He corresponded with Robert Bryce in mid-July.

ET: Your paper appears to be more good news with regard to natural gas. What are the key technologies that will be needed to deal with the low permeability challenges in tight gas reservoirs?

RFA: The technological solution starts with what we call GFREE. It refers to the advancement and integration of geoscience (G), formation evaluation (F), reservoir drilling, completion, and stimulation (R), reservoir engineering (RE), and economics and externalities (EE). This is the key to economically producing as much of this gas as possible. The Schulich School of Engineering at the University of Calgary recently developed this GFREE program, which is mission-oriented and multi-disciplinary, and it’s being advanced through cooperation with other universities, research institutions, and industry.

ET: How big are the potential tight gas resources in the U.S., and how do they compare to the known natural gas resources in the U.S.?

RFA: Based on our research, we find that the tight gas endowment rivals that of conventional gas. In the U.S., we’ve estimated the tight gas endowment at about 368 Tcf. This estimate only applies to the 14 U.S. petroleum provinces where there’s technically recoverable tight gas at present. We anticipate that this volume will grow substantially, probably to at least 1,000 Tcf. By way of comparison, the known conventional natural gas in all the U.S., based on the U.S.Geological Survey 2000 assessment, is 1,026 Tcf.

ET: Where are the biggest tight gas plays in the U.S. likely to be?

RFA: We believe that the conventional gas endowment is a proxy for the tight gas endowment in provinces around the world, including those 14 U.S. provinces mentioned earlier. So some of the important tight gas plays in the U.S. will be in the Permian, Anadarko, San Juan, East Texas, Arkoma, Southwest Wyoming, Wyoming Thrust Belt, Fort Worth, Piceance, Black Warrior, Denver, Wind River, Appalachian, and Big Horn basins.

ET: Your study points out that unconventional gas (like shale gas and coal bed methane) now accounts for about 40 percent of all U.S. gas production. That’s nearly a three-fold increase over unconventional gas production in 1990. How much could tight gas contribute to the overall percentage of U.S. gas output?

RFA: The U.S. D.O.E. estimates that by 2025, half of total U.S. gas production will come from unconventional gas sources. We believe that the majority of that share, probably 65 to 75 percent, will be coming from tight gas sands.

ET: Your paper states, “Where there is ‘conventional gas,’ there is also ‘tight gas.’” Why is this so?

RFA: There are many petroleum provinces around the world where this has been observed. For example, studies by the A.A.P.G. and I.I.A.S.A. have indicated that tight gas, like conventional gas, is present in nearly all of the world’s petroleum provinces. In the U.S. and Canada, there are 15 provinces recognized at present to contain technically recoverable tight gas. Our own study estimates the tight gas endowment in those 15 provinces at about 455 Tcf. We then estimate the conventional gas endowment using a variable shape distribution model in those same 15 provinces, and get a result of about 479 Tcf. So the conventional gas estimate is very similar to the tight gas estimate, which provides strong support for the statement that, generally, where there’s conventional gas, there’s tight gas in older rocks. This can also be visualized by considering a gas resource pyramid in a given petroleum province. The best quality reservoirs are at the top of the pyramid. Activation indexes are low and consequently these reservoirs are developed first. As we go down the pyramid, the reservoir quality deteriorates and gas recovery factors become smaller, but the volume of the pyramid becomes larger. The net result is volumes of tight gas that rival the endowment of conventional gas within a given petroleum province.

ET: In our conversations in Madrid, you discussed the idea that the 19th century was dominated by solid fuels (coal); the 20th century was dominated by liquid fuels (oil); but that the 21st century should be dominated by gaseous fuels. Why is that good news, and what (if anything) should be done to accelerate the transition toward gaseous fuels?

RFA: There are several reasons why that’s good news. First, natural gas is very abundant, probably more than oil and coal resources. Second, natural gas is clean. For example, when burned, it emits much lower levels of greenhouse gases. Third, gases are typically less costly to produce, partly because their production is less capital-intensive. The transition to gaseous fuels will depend on our actions as individuals, such as the mode of transportation we choose. Also, it depends on appropriate government policies that don’t cater to the fuels of the past. Our preliminary work using a global energy market (GEM) model suggests that we are on our way towards a methane economy that could pave the way to a hydrogen economy.