Methodology of CGPC's study of Canada's conventional gas resources

Nov. 26, 2001
The CGPC is a volunteer group of professionals with long experience in oil and gas exploration and resource assessment.

The CGPC is a volunteer group of professionals with long experience in oil and gas exploration and resource assessment. The committee's role is to make and publish high quality estimates of undiscovered gas resources.

CGPC does not undertake economic analyses, but its work is designed for use by companies and government agencies that wish to undertake gas supply studies based on geologically sound estimates of resource potential.

Exploration plays established by gas discoveries were assessed using a combination of geological judgment and statistical methodologies to estimate the volume of undiscovered gas and the size of undiscovered gas pools in each play. Industry and government agency participation in peer reviews of preliminary assessments contributed significantly to the credibility of the assessment process.

The committee used data on all 29,063 gas pools and gas fields across Canada, including as many as 42 items covering locations, depths, reservoir parameters, and gas analyses for each pool.

In western Canada assessments were based on individual gas pools except for some plays in the Foothills. In Foothills and Frontier plays, where structure is the dominant control on entrapment, assessments were made on the basis of gas fields rather than pools. Excel files holding input, output, and summary information on all of the assessed plays have been compiled on a play-by-play basis and are available on CD-ROM. The complete report, including maps and charts, is also available in linked PDF format.

Information from the discovered gas pools was used as the basic input for the assessment of gas potential in 107 exploration plays defined as Established Plays by these gas discoveries. The discovered pools in a play are used as a sample to predict the total population of pools. Knowledge of the geology of a play and the exploration history in terms of seismic definition, drilling history, and other factors serve to constrain the statistical analysis. No economic cutoffs were assumed, and each play area was assumed to be fully accessible.

Where no discoveries have been made, Conceptual Exploration Plays can be defined, and the geological configuration of potential traps, source rocks, and other factors are described. In such plays quantitative subjective assessments can be made where sufficient information about the geology and potential traps is available from seismic surveys and unsuccessful exploratory wells. These assessments have much more uncertainty attached to them than those for Established Plays.

CGPC assessed 12 Conceptual Plays in this manner in sedimentary basins off the east and west coasts. In addition, it defined 65 Conceptual Plays where there was not sufficient information to make quantitative assessments. These plays were described and qualitatively ranked within Assessment Regions. In total 184 exploration plays were recognized across Canada.

Undiscovered gas in place was estimated for each play. Gas in place is the volume of hydrocarbon and nonhydrocarbon gases in a reservoir rock in the subsurface. While this volume is important in terms of the geology of the play, it is the volume of gas that is available for market that is of most interest.

To estimate the volume of gas that might be marketable in each exploration play the percentage of gas in place that is marketable gas in the discovered pools was used to estimate the volume of marketable gas in the undiscovered gas pools in a play. The committee introduced the term Undiscovered Nominal Marketable Gas to describe estimates made in this way because the gas is marketable in name only. Not all of the Nominal Marketable Gas will actually be available, for the following reasons.

  1. No exploration is possible in parks, cities and towns, or other areas where exploration is precluded or restricted, so some of the predicted gas pools will never be found.
  2. All undiscovered gas pools are included in the assessment, but not all of these pools will be economic to explore for or to develop.
  3. Some pools will have too subtle a geological expression to be found.
  4. Not all gas pools or gas fields will have access to production and transportation infrastructure. This applies to Western Canada and in particular to Frontier Basins.

The actual amount of marketable gas will be less than the estimated amount of Nominal Marketable Gas, but we don't know how much less. This determination will require detailed economic analyses.

CGPC made no economic analyses, but the report is a unique source that will permit interested users to develop estimates of gas supply under different economic scenarios. However, even without detailed economic studies, examination of the volumes and pool size distribution of Nominal Marketable Gas estimates provides a good sense of the volume of gas that might be available and where it is located.

No estimates of Nominal Marketable Gas have been included for Conceptual Plays where no discoveries have been made. Such areas give no information on reservoir parameters, gas characteristics, or production history. Most important, there is a very high risk on each such exploration play that the play will fail completely. The principle is, "Don't count marketable resources in plays that are not established by discoveries."

Fig. 1 shows Canada's sedimentary basins. The gas producing and gas discovery areas are differentiated from areas where sedimentary rocks are present but where no discoveries have been made. The values on the map are the Nominal Remaining Marketable Gas in each area. The Nominal Remaining Marketable Gas is the volume of gas remaining after production to yearend 1998 plus the Undiscovered Nominal Marketable Gas.

Table 1 describes the distribution of Conventional Gas resources in Canada. It shows the gas in place, initial marketable gas, and remaining marketable gas for discovered and undiscovered resources. The endowment columns contain the sum of discovered and undiscovered resources.

In Table 1 areas that are more accessible for development are subtotaled to include the WCSB, Ontario and Quebec, and the Near Frontiers, while those less accessible are subtotaled as Remote Frontiers.

The bottom line shows the Conventional Gas resources in all categories. Table 2 summarizes these data. Tables 1 and 2 show the WCSB's dominance in the gas resource picture. It holds 142 tcf, 61% of the Remaining Nominal Marketable Gas in Canada.