Anticipating the Energy Crunch – Extracting Tight and Unconventional Gas
a report by
Roberto Aguilera
Professor, and ConocoPhillips-NSERC-AERI Chair, Schulich School of Engineering, Chemical and Petroleum Engineering Department, University of Calgary
I am glad the title grabbed your attention. What crunch? There is no crunch. The natural gas endowment is gigantic in the US and Canada and will last for several decades. The same holds true for the rest of the world. What appeared as a crunch possibility not too long ago has totally disappeared thanks to very creative technology to drill, hydraulically fracture and complete wells in unconventional gas formations, including tight gas, shales gas and coal-bed methane. In my experience, although this is not universally accepted, these unconventional formations share some common threads including large volumes of gas-in-place, low recovery factors and the presence of natural micro-fractures.
To investigate these matters we have created the geoscience, formation evaluation, reservoir drilling, completion and stimulation, reservoir engineering and economics and externalities (GFREE) multidisciplinary team at the University of Calgary.
Our general observation, as well as that of many researchers, is that where there is ‘conventional gas’ there is also ‘unconventional gas’, including tight gas and shale gas – and where there is coal there is gas. This observation leaves the pessimistic concept of peak gas in the near future totally off the mark. However, eventually there will be a maximum peak of natural gas production and, for that matter, of all hydrocarbons. The question is whether it will occur because of depletion or because of substitution with other sources of energy.
Geoscience (G) refers to the combination of geology, geophysics, geochemistry and hydrology. All of these disciplines are of paramount importance for the economical production of unconventional gas formations. Some of the aspects that must be taken into account in the evaluation of tight gas formations include folding, faulting, natural fracturing, in situ stresses, multilayer systems, mineralogy and petrology, connectivity and continuity, permeability barriers, net inter- bedded coals and shales. Formation evaluation (F) includes petrophysics, well testing and production decline analysis. Reservoir drilling completion and stimulation (R) refers to technology developed for drilling horizontal wells, multistage hydraulic fracturing jobs and properly completing the formations to avoid formation damage. Reservoir engineering (RE) includes key issues such as material balance evaluations and numerical simulation. Finally, economics and externalities (EE) refers to concentrating on research that has the capability of generating economic results, and undertaking it responsibly from social and environmental points of view.
One school of thought at present indicates that tight gas is found in basin-centre or continuous gas accumulations. However, there is an opposing point of view indicating that most tight gas fields occur in low-permeability reservoirs in conventional structural, stratigraphic or combination traps that are usually referred to as ‘sweet spots’. Our observation is that low-permeability reservoirs can occur in both basin-
© TOUCH BRIEFINGS 2010
centred and conventional accumulations; assuming that one or the other is always present is not wise. Generalisations might lead to potential fiascos. For example, the assumption of a continuous accumulation in an instance where tight gas is really in a conventional structural trap might lead to significant overestimation of the volumes of gas-in-place. To avoid such potential fiascos it is better to consider each tight gas formation as a research project by itself.
In the case of gas shales we go back for almost two centuries. The first shale well was drilled in 1821 in Chautauqua County, New York. The well is reported by the US Geological Survey (USGS) to have produced natural gas through natural fractures mainly for local use. That first well introduced the key element of natural fractures for successful production of natural gas. In our opinion, the same key element holds true today and is partially responsible for the revolution in gas production we are witnessing, particularly in the US and Canada. Hydraulic fracturing these naturally microfractured reservoirs leads to the gargantuan reservoirs we are pursuing today with horizontal wells. These reservoirs will be an important part of the North American and, eventually, global energy landscape for decades to come.
The positive part of the previous observations is that that there is plenty of gas throughout the world. The negative part is that this abundance has created a bubble that has led to very low gas prices. However, here is where opportunities, driven by creativity, might come into play. There are means of putting these gigantic volumes of gas to good use. As an example, a large number of vehicles in the US could be manufactured or be retrofitted to run on compressed natural gas (CNG). The benefits would come in the way of a reduction of oil imports with resulting associated savings, some increases in the price of natural gas, less pollution (particularly in large cities) and reductions
of CO2 emissions. Unfortunately, this is not mentioned explicitly in the new Waxman-Markey energy bill. The opportunity might be lost to put the gigantic gas endowment discussed above to good use.
Roberto Aguilera is a Professor and ConocoPhillips-NSERC- AERI Chair in the Schulich School of Engineering, Chemical and Petroleum Engineering Department at the University of Calgary, Canada, He is also Executive Editor of the SPE
Journal of Canadian Petroleum Technology (JCPT), a principal of
Servipetrol Ltd and a Director of Junex in Quebec. He was an AAPG instructor on the subject of naturally fractured reservoirs from 1984 to 1996. He has lectured, presented his course entitled Naturally Fractured Reservoirs and/or
has rendered consulting services in 50 countries throughout the world. Professor Aguilera is a Distinguished Author of the Journal of Canadian Petroleum Technology (1993 and 1999), a recipient of the Outstanding Service award (1994) and the Distinguished Service Medal (2006) from the Petroleum Society of CIM and a Society of Petroleum Engineers (SPE) Distinguished Lecturer on the subject of naturally fractured reservoirs for 2000–2001. He holds an MSc and PhD in petroleum engineering from the Colorado School of Mines.
E:
r.aguilera@ucalgary.ca
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Natural Gas
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