The Energy Ratio Limit

Growing up during the Lower Diluvian epoch, when my father got us out of bed to watch Sputnik blink across the sky as the world’s first satellite and we began to learn new math instead of arithmetic, gasoline for the family dinosaur cost about $0.33/gallon. Since then, inflation has raised the price of U.S. postage stamps from $0.04 to $0.44, the model airplanes I bought as a youth for $1.06 now cost about $15, and the cost of groceries has increased significantly.

By these subjective measurements, in the United States that $0.33 gallon of gasoline should now cost well over $3 just to account for inflation, with an additional price bump to cover the fact that oil and gas have become harder to find and produce. Believe it or not, gasoline and other hydrocarbon products are better bargains now than they were 50 years ago, and given the improved fuel economy of modern cars we probably spend a lower percentage of our income on gasoline than we did back then.

Even so, many complain about the price of hydrocarbons, unwilling to allow for the fact that the oil and gas industry is a business that depends on an economic return for the effort. We don’t explore for oil and gas just for the sake of proving theories about the presence/absence of an oil pool, even though that is the fun, scientific part of the job. And since an economic return is necessary, known fields containing millions of barrels of oil remain untapped because it would cost more to extract and transport the oil than could be recovered by its sale. Such dollar limits change with product prices, thus many such fields can and will be produced when prices for oil and gas increase.

However, there is a different and less flexible energy-budget limit involved in the production of fossil fuels. As long as oil is being recovered for use primarily as an energy source, no one can afford to expend the amount of energy found in a barrel of oil in order to drill for, pump out, and transport less than a barrel of oil.

Jeremy Boak is the new chair of the AAPG Energy Minerals Division Oil Shale Commodity Committee, and professor at the Colorado School of Mines. According to Boak, the ratio between 1) the energy expended in obtaining oil, and 2) the energy recovered by the process* was probably 1:100 or better for new wells in the era of easy oil, but the ratio has fallen to 1:20 or even 1:10 as that oil has been depleted. The ratio is even less for mature fields that require advanced oil recovery techniques, where Boak suggests that the ratio is below 1:10. So far, efficiency gains through better science and technology have kept the ratio from declining to the point where, as with corn-based ethanol, it’s debatable whether a net energy benefit exists.

Ultimately, even when over half the oil remains in the ground, industry makes the decision to abandon a field when it takes more money and energy to recover the oil than can be extracted from the recovered oil. And with many conventional fields reaching their production capacity limits we are again looking at extracting fossil energy from the immature kerogen in oil shale formations, where Boak says the energy-in/energy-out ratio is only between 1:3½ and 1:5. The renewed interest in this and other unconventional resources is an indirect indication both of industry’s internal forecasts for energy demands and of how close to the bone we are getting.

Rising oil prices will only go so far in promoting recovery of the world’s fossil energy resources. The laws of physics limit how much oil and gas can be recovered from small, deep, or remote fields as long as we don’t intend to put more energy into the ground than we extract from it. Once we develop reliable and inexpensive alternative energy sources we may use hydrocarbons primarily for purposes such as chemical feedstock instead of merely burning them, whereupon they could conceivably become more valuable than the energy they contain. In the meantime, our job as geologists is to use the best available geoscience when picking drilling locations and determining completion techniques. Every day, AAPG members are advancing the science and technology that help keep the energy ratio favorable.

* Described as the “EROI,” the energy return on investment, by Cleveland, C.J., 2005, “Net energy from the extraction of oil and gas in the United States,” Energy, v. 30, p. 769-782.

Comments (0)

 

President's Column

President's Column - John Lorenz

President's Column

President's Column - Ted Beaumont

Edward A. "Ted" Beaumont, AAPG President (2012-13), is an independent consultant with Cimarex Energy.

President's Column

President's Column - Paul Weimer

Paul Weimer, AAPG President (2011-12), is a geology professor at the University of Colorado, Boulder.

President's Column

AAPG Presidents offer thoughts and information about their experiences for the Association. 

VIEW COLUMN ARCHIVES

See Also: Bulletin Article

Predicting the presence and connectivity of reservoir-quality facies in otherwise mud-prone fluvial overbank successions is important because such sand bodies can potentially provide connectivity between larger neighboring sand bodies. This article addresses minor channelized fluvial elements (crevasse-splay and distributary channels) and attempts to predict the connectivity between such sand bodies in two interseam packages of the Upper Permian Rangal Coal Measures of northeastern Australia. Channel-body percent as measured in well logs was 2% in the upper (Aries-Castor) interseam and 17% in the lower (Castor-Pollux) interseam. Well spacing were too great to allow accurate correlation of channel bodies. The Ob River, Siberia, was used as a modern analog to supply planform geometric measurements of splay and distributary channels so that stochastic modeling of channel bodies was possible. The resulting models demonstrated that (1) channel-body connectivity is more uniform between minor distributary channels than between crevasse-splay channels; (2) relatively good connectivity is seen in proximal positions in splays but decreases distally from the source as channel elements diverge; and (3) connectivity tends to be greater down the axis of splays, with more isolated channel bodies occurring at the margins.
Desktop /Portals/0/PackFlashItemImages/WebReady/prediction-of-channel-connectivity-and-fluvial.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 5768 Bulletin Article

Sequence stratigraphy and coal cycles based on accommodation trends were investigated in the coal-bearing Lower Cretaceous Mannville Group in the Lloydminster heavy oil field, eastern Alberta. The study area is in a low accommodation setting on the cratonic margin of the Western Canada sedimentary basin. Geophysical log correlation of coal seams, shoreface facies, and the identification of incised valleys has produced a sequence-stratigraphic framework for petrographic data from 3 cored and 115 geophysical-logged wells. Maceral analysis, telovitrinite reflectance, and fluorescence measurements were taken from a total of 206 samples. Three terrestrial depositional environments were interpreted from the petrographic data: ombrotrophic mire coal, limnotelmatic mire coal, and carbonaceous shale horizons. Accommodation-based coal (wetting- and drying-upward) cycles represent trends in depositional environment shifts, and these cycles were used to investigate the development and preservation of the coal seams across the study area.

The low-accommodation strata are characterized by a high-frequency occurrence of significant surfaces, coal seam splitting, paleosol, and incised-valley development. Three sequence boundary unconformities are identified in only 20 m (66 ft) of strata. Coal cycle correlations illustrate that each coal seam in this study area was not produced by a single peat-accumulation episode but as an amalgamation of a series of depositional events. Complex relations between the Cummings and Lloydminster coal seams are caused by the lateral fragmentation of strata resulting from the removal of sediment by subaerial erosion or periods of nondeposition. Syndepositional faulting of the underlying basement rock changed local accommodation space and increased the complexity of the coal cycle development.

This study represents a low-accommodation example from a spectrum of stratigraphic studies that have been used to establish a terrestrial sequence-stratigraphic model. The frequency of changes in coal seam quality is an important control on methane distribution within coalbed methane reservoirs and resource calculations in coal mining. A depositional model based on the coal cycle correlations, as shown by this study, can provide coal quality prediction for coalbed methane exploration, reservoir completions, and coal mining.

Desktop /Portals/0/PackFlashItemImages/WebReady/accommodation-based-coal-cycles-and-significant.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 5686 Bulletin Article

See Also: DL Abstract

Earth modeling, from the construction of subsurface structure and stratigraphy, to the accurate understanding of rock physics, through the simulation of seismic and nonseismic responses, is an enabling technology to guide decisions in acquisition, processing, imaging, inversion and reservoir property inference, for both static and time-lapse understanding. So it is crucial to capture those earth elements that most influence the geophysical phenomena we seek to study. This is notoriously difficult, probably because we regularly underestimate how clever the earth can be in producing various geophysical phenomena.

Desktop /Portals/0/images/_site/AAPG-newlogo-vertical-morepadding.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 3090 DL Abstract

See Also: Field Seminar

Participants will learn through the use of spectacular outcrops, subsurface datasets, and stratigraphic modeling how these systems tracts and key surfaces (flooding surfaces and sequence boundaries) may be recognized.

Desktop /Portals/0/PackFlashItemImages/WebReady/fs-sedimentology-and-sequence-stratigraphic-response-of-paralic-deposits.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 86 Field Seminar

See Also: Learn! Blog

This forum is an intensive one-day review by experts of the latest findings regarding the productive extent and producibility in the Granite Wash of Oklahoma and Texas, along with Pennsylvanian sand-producing horizons.

Desktop /Portals/0/PackFlashItemImages/WebReady/forum-granite-wash-and-pennsylvanian-sand-hero.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 11123 Learn! Blog