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Tuesday, November 06, 2007

Dispersive Natural Gas Discoveries

As a follow-up to the last post on the Dispersive Discovery model, I decided to apply the same technique to US Natural Gas discoveries.

As background, I found a few references which said "The United States has proved gas reserves estimated (as of January 2005) at about 192 trillion cubic feet (tcf)" and from NETL this:
U.S. natural gas produced to date (990 Tcf) and proved reserves currently being targeted by producers (183 Tcf) are just the tip of resources in place. Vast technically recoverable resources exist -- estimated at 1,400 trillion cubic feet -- yet most are currently too expensive to produce. This category includes deep gas, tight gas in low permeability sandstone formations, coal bed natural gas, and gas shales. In addition, methane hydrates represent enormous future potential, estimated at 200,000 trillion cubic feet.
This together with the following reference indicate the current estimate of NG reserves lies between 1173 and 1190 TCF (Terra Cubic Foot = 1012 ft3).

How much Natural Gas is there? Depletion Risk and Supply Security Modelling

US NG Technically Recoverable Resources US NG Resources
(EIA, 1/1/2000, Trillion ft3) (NPC, 1/1/1999, Trillion ft3)
--------------------------------------- -----------------------------
Non associated undiscovered gas 247.71 Old fields 305
Inferred reserves 232.70 New fields 847
Unconventional gas recovery 369.59 Unconventional 428
Associated-dissolved gas 140.89
Alaskan gas 32.32 Alaskan gas (old fields) 32
Proved reserves 167.41 Proved reserves 167
Total Natural Gas 1190.62 Total Natural Gas 1779

Free Image Hosting at www.ImageShack.usHubbert originally plotted yearly discoveries per cumulative footage drilled for both oil and natural gas. I also found a curve for Natural Gas at this reference (may be the same one as found by McManus).

Interesting that if we fit the cumulative discovery data to the naive exponential that the curve matches very well on the upslope (see below) but that the asymptote arrives way too early, obviously missing all the dispersed discoveries covered by the alternative model. The dispersive discovery adds a good 20% extra reaching an asymptote of 1130, coming much closer to the value from NETL of 1190.

Although a bit unwieldy, one can linearize the dispersive discovery curves, similar to what oil analysts do with Hubbert Linearization. Although it swings wildly initially, I can easily see the linear agreement with a correlation coefficient very nearly one and a near zero extrapolated y-intercept.

As a comparison, I plotted the previously discussed fits for USA oil discoveries and found the same general agreement in linearization between NG and oil.

(note that the naive exponential that Hubbert used below overshoots the fit to better match the asymptote but still falls short of the alternative model's asymptote, and which also fits the bulk of the data points much better)

Every bit of data tends to corroborate that the dispersive discovery model works quite effectively in both providing an understanding on how we actually make discoveries in a reserve growth fashion and in mathematically describing the real data.

note: on some of the charts, the correlated fit does not show the decimal points in the linear equations due to a bug in the plotting program.


Professor Blogger Jerry McManus said...

That's a great find on the nat. gas data, and amazing work on the analysis. Thanks for the superb effort.

Here's what Hubbert had to say about US nat. gas in the article from 1976 that I've been referring to:

Estimates of the ultimate cumulative production of natural gas in the United States have been made on the basis both of the ratio of gas discoveries to crude oil discoveries and the prior estimate of Qt for oil, and of gas discoveries per foot of exploratory drilling. These methods give a range from about 1 X 10^15 to 1.1 X 10^15 ft3 (1 ft^3 = 0.02832 m^3) for Qt for natural gas for the conterminous United States. The peak in natural-gas proved reserves was reached in 1967, and the peak in the production rate occurred in 1973.

Estimates of natural-gas liquids are obtained from the prior estimates for natural gas and the gas-to-liquids ratio. For the conterminous United States, the estimated value for Qt for natural-gas liquids is about 34 X 10^9 bbl, of which 15.6 X 10^9 bbl had been produced by the end of 1974.

For Alaska, which is still in its early stages of petroleum exploration, only rough estimates can be given at present of the ultimate quantities of petroleum fluids that may be produced. Including both land and offshore areas, such rough estimates are the following: crude oil, 43 X 10^9 bbl; natural gas, 134 X 10^12 ft; natural-gas liquids, 5 X 10^9 bbl.

Table 1 gives a summary of the approximate magnitude of the ultimate quantities of crude oil, natural gas, and natural-gas liquids, and their energy contents, to be produced in the United States and the bordering continental shelves:

Crude Oil: 10^9 bbl
Conterminous United States: 170
Alaska: 43
Total United States: 213

Natural-gas liquids: 10^9 bbl
Conterminous United States: 34
Alaska: 5
Total United States: 39

Total Hydrocarbon liquids: 10^9 bbl
Conterminous United States: 204
Alaska: 48
Total United States: 252

Natural Gas: 10^12 ft^3
Conterminous United States: 1050
Alaska: 134
Total United States: 1184

I have an e-mail in to the editors at TOD asking if they would like to publish excerpts from the article, but no word back yet. I also published an offer on the aforementioned TOD thread to send a link to the transcribed version, but so far only one taker has replied.


12:07 PM  
Professor Blogger WHT said...

Jerry, This info is way too cool. Thanks

8:03 PM  
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Professor Anonymous Amrit Ray said...

really nice post.

5:29 AM  
Professor Blogger M. Simon said...

With new low cost drilling methods and new fields discovered the US in the past year has enough natural gas to last for 100 years at current rates of use.

Gas supply increased 9% in the past year.

With prices low the amount of exploration has declined so there may be even more gas than currently inventoried.

Of course we will have to transition away from gas over time. The new gas discovered gives us a nice cushion though.

9:44 AM  

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