SUCCESSES IN 1980s BODE WELL FOR W. CANADA SEARCH

P.J. Lee, Paul R. Price
Geological Survey of Canada
Calgary

The senior author made a prediction in 1980 of how much initial established recoverable crude oil (light, medium, and heavy) and initial established marketable natural gas would be discovered in the Western Canada sedimentary basin (WCSB) in the 1980s.

The data used for that prediction included the annual cumulative footage drilled in meters and the cumulative volumes of crude oil and marketable gas discovered annually as reported in the 1980 Canadian Petroleum Association Statistical handbook.1

Geological Survey of Canada (GSC) performed regression analyses on these data sets in order to predict future oil and natural gas discoveries in the WCSB. It released these predictions to the public as GSC Open-File Report No. 767.2

After a decade of further exploration, it is now appropriate to compare the 1980 predictions against the past decade's results using data from the 1990 CPA Statistical Handbook and the relevant publications of the Manitoba, Saskatchewan, Alberta, and British Columbia governments.

This paper compares the results of the 1980 predictions with the results from the 1980s and displays the current oil and gas reserve picture of the basin in terms of the distribution of the discoveries at the end of 1979 and 1988 respectively, both stratigraphically and by pool class size.

PREDICTION VS. RESULTS

The 1980 predictions and actual results for the decade of the 1980s are shown (Table 1).

The data used to make the predictions and the comparisons were obtained from the CPA Statistical Handbook.1 3 There is an obvious correlation between exploratory drilling and the addition of reserves to the oil and gas reserve base.

The more exploration footage that is drilled, the higher the chance that new quantities of commercial hydrocarbons will be found. Many factors influence the amount of footage that will be drilled during a given year, not the least of which are favorable political and economic conditions such as the presence of sufficiently high oil and gas prices.

The 1980 prediction of exploratory footage to be drilled during the decade was based on two assumptions:

exploratory drilling in the basin would continue at a pace similar to that of the 1970s (that is, the authors assumed that exploratory drilling would continue at an average of 2,000 wells/year); and
that there is a relationship between the footage drilled in any given year and the volume of hydrocarbons found.

Reserve data in the form of cumulative initial established recoverable oil and cumulative initial established marketable gas discovered per year prior to 1980 were plotted separately against the respective cumulative exploration drilling footage by year.

The cumulative oil reserve data in billions of barrels is plotted as a function of time in years (Fig. 1a), and the cumulative gas reserve data in trillions of cubic feet are plotted as a function of time in years (Fig. 1b).

From this data and assumed exploratory drilling of 2,000 wells/year, GSC estimated the volumes of hydrocarbons to be found in the 1980s by performing a regression analysis on the data sets.

It is obvious that several factors could influence the assumptions and thereby the estimates. Changes in exploration technology influence the overall level of exploration risk and therefore the number of exploratory wells drilled.

Furthermore, the effect of changes in the economic and political factors during the last decade on the number of wells drilled and the volumes of hydrocarbons found were not analyzed. These factors are often difficult to predict within reasonable limits.

However, even with these "noise" factors in mind, the 1980 predictions displayed in Table 1 are very close to the actual exploration results despite the turbulent oil and gas prices, political climate, and unforeseen technological advances during the decade.

POOL SIZES, DISTRIBUTIONS

One approach to examining the changes in the basin's overall reserve picture from 1980 to 1988 is to look at 1979 and 1988 snapshots of the stratigraphic distribution of the discovered pools, and how these pools are proportioned according to class sizes.

GSC compiled crude oil and natural gas pools discovered through the end of 1979 and through 1988 according to their pool class size and stratigraphic system.

GSC obtained the pool data presented in Tables 2, 3, 4, 5, 6, and 7 and Figs. 2 and 3 from the various publications of provincial agencies.4 5 6 7 8 9 10

OIL RESULTS

During the 1980s, 2.2 billion bbl of initial established recoverable oil were discovered and are spread among some 2,942 pools.

From an examination of Tables 2, 3, and 4, the following statements can be made:

Four of the oil pools discovered in the 1980s have recorded reserves greater than 10 million bbl, compared with 192 discovered prior to 1980 (Tables 2, 3);
A total of 1,959 oil pools discovered during the 1980s recorded reserves less than 100,000 bbl. From this data it is clear there is a trend towards the discovery of smaller oil pools (Fig. 2).
The total number of oil pools discovered in the 1980s is slightly more than that discovered prior to the 1980s, but the volume of additional reserves discovered is only about 13% of the total oil reserves discovered through the end of 1988;
Table 3 clearly shows that during the 1980s pools of significant size were discovered within strata of Devonian and Upper Cretaceous age.

These strata are still considered the most promising oil exploration targets.

GAS RESULTS

Examination of Tables 5, 6, and 7 reveals the following insights concerning natural gas reserve data:

The 32 tcf of marketable gas discovered in the 1980s is allocated in 8,849 gas pools and comprises about 24% of the total gas reserves discovered in the basin;
Three of the gas pools discovered in the 1980s have marketable gas reserves of more than 100 bcf;
There is also a trend towards the discovery of smaller gas pools, but the shift is not as dramatic as that shown for the oil reserve picture (Fig. 3).
Table 6 shows that during the 1980s pools of significant size were discovered within strata of Lower Cretaceous, Permo-Carboniferous, and Devonian age. The authors believe that these horizons will remain promising natural gas exploration targets for some time.

ACKNOWLEDGMENTS

The authors thank Gerry Reinson, Kirk Osadetz, and Fred Trollope for their valuable comments and stimulating discussion that led to the refinement of this paper and Peter Gubitz for his assistance with the drafting of the figures. The authors extend special thanks to Stephan Rodriques, statistician for the Canadian Petroleum Association, for his valuable assistance with the collection and interpretation of the CPA data.

REFERENCES

Canadian Petroleum Association, CPA Statistical Handbook, 1980, Tables 8 and 10, Section 11, Calgary, Alta.
Procter, R.M., Lee, P.J., and Skibo, D.N., Canada's Conventional Oil and Gas Resources, GSC Open file 767, March 1981, Department of Energy, Mines and Resources Canada.
Canadian Petroleum Association, CPA Statistical Handbook 1990, Tables 15 and 17, Section 11, Calgary, Alta.
Alberta Energy Resources Conservation Board, ERCB ST89-18, December 1988, Alberta's Reserves of Crude Oil, Oil Sands, Gas, Natural Gas Liquids, and Sulphur, 1989, Calgary, Alta.
British Columbia Ministry of Energy, Mines and Petroleum Resources, 1988 Hydrocarbon Reserves Tape, 1989, Victoria, B.C.
Manitoba Department of Energy and Mines Annual Report 1980, Mineral Resources Division, Winnipeg, Man.
Manitoba Department of Energy and Mines, Annual Report 198889, Mineral Resources Division, 1989, Winnipeg, Man.
Manitoba Energy and Mines, Mineral Education Series, MG 1 3505 Oil in Manitoba, 1988, Winnipeg, Man.
Saskatchewan Energy and Mines, Petroleum and Natural Gas, Miscellaneous Report 84-1, Reservoir Annual 1983, 1984, Regina, Sask.
Saskatchewan Energy and Mines, Petroleum and Natural Gas, Miscellaneous Report 89-1, Reservoir Annual 1988, 1989, Regina, Sask.
GSC: Western Canada To Stay Key Search Area, OGJ, Vol. 79, July 6, 1981, p. 80.