I will make a few comments on the exploration case history of the Cold Lake, Alberta, oil sands deposit, which presently is estimated to contain more than 32 X 109 m3 (200 X 109 barrels) of bitumen in place. I believe that it is worthwhile to examine the history of “discovery” and the early stages of evaluation of this huge heavy-oil resource because it may have some application to other sedimentary basins that are in an earlier stage of petroleum exploration. During part of the period of early delineation of Cold Lake (from November 1962 to May 1965), I was in charge of geological assessment of oil sands (other than Athabasca) and heavy oil for Imperial (Esso).
By 1961, most of the heavy-oil deposits in western Canada had been recognized and delineated. Exposures of the Athabasca oil sands had been reported by explorers of the Athabasca River as early as 1778. In 1961, exploration and assessment of this trillion-barrel (160 X 109 m3) deposit was fairly well advanced. Bitumen in basal Cretaceous sands at Peace River, now assessed at 11 X 109 m3 (70 X 109 barrels) in place, had been delineated in the course of exploration for Devonian reefs during the 1950s. The Wabasca deposits, a downdip extension of the Athabasca oil sands, had been discovered and were known to contain at least 5 X 109 m3 (30 X 109 barrels) of oil in place. Most geologists familiar with northern Alberta were aware of viscous oil occurring in Grosmont and other carbonates below the sub-Cretaceous unconformity. Heavy oil had been produced commercially at Lloydminster since 1943.
In 1961, Imperial assessed the situation as one of declining conventional reserves in western Canada. Management decided to examine the feasibility of developing large reserves based on thermal or other in situ recovery of heavy oil or bitumen from oil sands other than Athabasca. Imperial was already involved at Athabasca in two consortiums, one of which evolved into the Syncrude surface mining project. Imperial’s land position on other known oil sand deposits and in the Lloydminster heavy-oil area was not encouraging. Shell held a commanding land position at Peace River, Gulf had large holdings at Wabasca, and Husky was solidly entrenched in the Lloydminster area.
During the fall of 1961, Jim McAlary (an exploration geologist for Imperial) was given the task of searching for “new” heavy oil in an area where Imperial could develop a sizeable land position. As part of the study,Jim pulled the logs and other data on several hundred wells between Athabasca and Lloydminster. He found two wells, 37 km (23 mi) apart, with resistivity logs that suggested thick sections (15-25 m [49-82 ft]) of hydrocarbon saturation in Mannville (Lower Cretaceous) sands. The northern well, drilled in 1954, had no cores or tests. The southern well, drilled in 1957, had been cored and yielded oil-cut mud on drillstem tests. The southern well had been cased and the oil sands perforated but production tests were negative, apparently because of the high viscosity of the oil. The study done by McAlary strongly suggested a correlation between the thick oil sands in the two wells. Large blocks of land were open for filing in the area at that time, so that the high-grade areas outlined by McAlary were obtained by Imperial in early 1962.
In September 1962, Imperial drilled offsets to the two wells identified by McAlary in order to confirm that oil saturation was present and to assess the reservoir in a preliminary way. These two wells (Imperial Beaverdam 2-26-60-2 W4M and Imperial Ethel Lake 10-22-64-3 W4M) led directly to the recognition and delineation of the Cold Lake heavy-oil deposit. Oil sands in the wells were cored, production casing was set, and some of the oil sands were perforated. Bailing yielded a small amount of extremely viscous heavy oil.
Imperial acquired sizeable land holdings in the area. During the winter of 1962-1963, as I recall, we drilled and assessed eight wells in the Cold Lake area of Alberta and five wells across the border in Saskatchewan. During the following two winters, we must have added an additional 20-30 delineation and assessment wells. By 1965 we had outlined a major oil sand deposit known to underlie more than 3000 km2 (1100 mi2). In some of the wells, we had found aggregate net thickness of oil sand of more than 60 m (200 ft). By 1965, oil in place at Cold Lake was assessed at more than 12 X 109 m3 (75 X 109 barrels; Vigrass, 1965, 1968).
Figures & Tables
Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.