Assessment of Alberta’s Crude Bitumen Resources
R. A. Marsh and T. M. Hurst
Alberta Energy and Utilities Board, Calgary, AB, Canada
The mission of the Alberta Energy and Utilities Board (EUB), an independent quasi-judicial government body whose energy roots were created in 1938, is to ensure the discovery, development, and delivery of Alberta’s energy resource and utilities services take place in a manner that is fair, responsible, and in the public interest. It has two main functions; to regulate the energy and utility industries and to provide related information, including resource assessments, to the public, industry, and government. In making regulatory decisions regarding crude bitumen development the EUB employs geological and engineering staff to review the technical merits of industry applications. In doing this they independently evaluate, delineate, analyze, and assess resources and reserves that might be subjected to development. These same staff also fulfill the EUB’s resource appraisal mandate by using the knowledge of industry practices combined with their own evaluation of the data to estimate and report on the resources and reserves of the entire province. It annually publishes these estimates in a reserves and supply/demand report for all energy resources. The current edition is ST98-2007: Alberta’s Reserves 2006 and Supply/Demand Outlook 2007-2016 and is available on the EUB’s website. This work is possible because in Alberta the energy industry is required to submit exploration and development data to the EUB. It is the collection, evaluation, analysis, and dissemination of data and information that is the cornerstone in the EUB’s ability and responsibility to conduct resource assessments.
Background and Previous Work
A sizeable portion of the world’s hydrocarbon endowment consists of non-conventional oil. In Canada, it mostly takes the form of bitumen (extra heavy oil that will not flow to a well under normal reservoir conditions) in unconsolidated to poorly consolidated clastic reservoirs (oil sands). Large quantities exist in Alberta with much smaller amounts in western Saskatchewan. Significant quantities also exist within Alberta in underlying carbonates that are in contact with the sands. Bitumen is known to occur in eleven different horizons and its extent is legally defined by the EUB in 15 Oil Sand Deposit (OSD) orders which are grouped together by 3 Oil Sands Area (OSA) orders. The latest summary of the in place resources, listed by area and deposit, are shown in Table 1.
Since the early 1960s the EUB and its predecessors have published assessments of Alberta’s bitumen occurrences. Major assessments were completed in 1963, 1977, 1981, 1985, and 2000. Updated assessments were published in 1982, 1991, and 1996. Information in these reports has varied but has included sedimentology, stratigraphy, cross-sections, isopach and structure contour maps, oil quality, reserves terminology, in place resource and recoverable reserve volumes. Volumes have been classified by area, depth, and saturation. More recently, volumes have been calculated on a ‘total’ in place basis and on a ‘developable’ in place basis as well. Starting in 2000 (for year-end 1999), a deposit wide 20% recovery factor has been applied to ‘developable’ in place volumes suitable to in situ development to estimate Alberta’s established reserves. This change resulted in the initial established reserves jumping from 7.3 109m3 (45.9 billion barrels) to 28.3 109m3 (178.3 billion barrels). In originally selecting the 20% recovery factor the EUB took into consideration that while the Steam Assisted Gravity Drainage (SAGD) development history had been very brief, commercial Cyclic Steam Stimulation (CSS) operations had been in existence for almost 20 years. The first estimate of recoverable bitumen from mining was made in 1963. The mineable recovery factor is more site-specific and is based on commercial mines in operation since the early 1960s. It currently averages around 60 per cent.
Over the last five decades the OSAs have been extensively explored. While some of this exploration has been focused on bitumen, and oil (and gas) beneath the bitumen-bearing strata, until very recently, the majority of the information available to assess Alberta’s bitumen resources has come from exploration for natural gas within the same strata as the bitumen. Because of this extensive exploration the EUB’s resource appraisal work has almost exclusively been focused on refining and revising estimates as more wells are drilled within the existing deposits.
Preceding and immediately following the 2000 re-assessment of Alberta’s established reserves, little attention was paid to the province’s bitumen reserves estimates. With the concern in recent years on global oil supplies (as demonstrated by the peak oil debate) and the general acceptance of large bitumen volumes in Alberta, greater notice is being given to the EUB’s resource assessments. Additionally, concerns regarding the ability to produce bitumen in the presence of depleted gas caps have led to a lengthy technical and regulatory review. As a result of these issues, the EUB has increased its focus on bitumen, particularly in situ, and has dedicated significant new effort to updating each deposit. So far, the re-assessments of the Athabasca Wabiskaw-McMurray, the Cold Lake Clearwater, and, just recently, the Peace River Bluesky-Gething deposits have been completed. Given the continuing evolution in recovery methods, the short development history of SAGD, and other factors (such as gas/bitumen, impact on water, and gas supplies), the EUB has decided to currently only update the in place resources. Updates to the established reserves will occur at a later date.
In re-assessing the in place bitumen resources EUB staff build upon the existing geological knowledge by defining a stratigraphic model for a deposit (based on well logs, core, and existing publications) and by picking the tops of all relevant surfaces in virtually all the wells (normally numbering in the thousands). They then iteratively conduct a geological analysis using the stratigraphic model, and structure and reservoir isopach maps, to resolve problems and to identify the zones containing bitumen. EUB staff also petrophysically evaluate nearly all wells with a suitable suite of logs on an incremental 0.30m (1 foot) basis and store the interval data containing bitumen mass per cent, water saturation, effective porosity, and volume of shale elements in large computer systems. Core and core analyses are used to validate and calibrate the petrophysical log analyses. Mapping of the averaged individual interval data elements and bitumen isopachs at differing bitumen mass per cent cut-offs are used to better understand the reservoir and to find and resolve problems. Standardized cut-offs (for thickness and bitumen mass per cent) are applied to determine in place resources. Bitumen volumes are calculated on both a zonal and cumulative basis to better define the developable in place quantities from the total in place. Recovery factors are normally applied to the developable in place volumes.
While work will continue on updating the in place resources for the other 12 deposits, the main focus will be on reviewing the parameters and criteria to determine the recoverable portion of the in place resource. This is complicated by the fact that potential development of the bitumen in carbonate reservoirs appears to be just beginning (as witnessed by the significant dollars spent on leasing portions of the Grosmont deposit in 2006).
In the work ahead on in situ resources the EUB intends to make use of 3D reservoir models and intends to conduct increased analysis of existing commercial project areas, as is currently the case for mineable resources.
The EUB and its predecessors have conducted resource assessments of Alberta’s bitumen resources for many decades and continue to improve its knowledge of the geology, development practices, and environmental and economic impacts. In recent years the pace of exploration and development has been very strong and the EUB has responded by engaging in significant new efforts to provide new re-assessments. The EUB believes that its ability and responsibility to conduct and publish resource assessments is crucial in ensuring that good decisions are made regarding the development of Alberta’s crude bitumen resources in the public interest.
AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada