Review of the world's major oil sand deposits

The solution of today's energy equation lies in crash programmes for the development of alternative fuels to supplement dwindling conventional oil reserves. Conse quently, sources of non-conventional oil such as oil sands, oil-shale and coal are being given greater consid eration. The production of syncrude from oil sands is technologically further advanced than recovery from oil- shale and coal. Oil sands is a term loosely applied to a wide variety of deposits containing heavy hydrocarbons that chemically are the same as conventional oils but which have low gravities and high viscosity. These char acteristics prevent their development by conventional oil-well techniques. In any event, they are what the name implies sandstone impregnated with heavy oil. Oil sand deposits are present in many parts of the world (Figure 1). Many of them have been the object of aca demic study, others have been studied because their occurrence was thought to indicate the presence of con ventional oil. The time has passed when oil sand areas were the object of speculative land investment. At present the developments in Athabasca show that Canada is emerg ing as a testing ground for the economics and technology of a new era in oil production. However, developments of the resource inside and outside Canada will be affected in several ways: 1) The cost of a 100,000 bbl/day (16,365 m3) plant may be as much as $1 billion. This will be beyond the eco nomic resources of many of the countries in which most deposits occur. 2) The requirement for specialist knowledge, skilled labour, specialist materials, equipment and other re sources will restrict severely the number of plants that could be commissioned at any one time. 3) The remoteness of deposits, the inaccessibility to water, the long development lead times and the presence of alternative resources in larger quantities (for example, oil-shale in the U.S.A. and coal as in Africa) must influ ence the rate of development of the oil sand resources which occur in these countries. 4) Conservation and preservation are key words which in some parts of the western world might well delay the development of mineable deposits until an economic in-situ method of recovery is discovered. The increasing dependence of the U.S.A. on oil imports means that oil sand projects will be progressively developed over the next two decades for North Ameri can markets. The best prospects for early development, besides the surface-mineable oil sands of Athabasca, are the deposits in the U.S.A. (depending on the rate at which oil-shale technology develops) and perhaps, con currently, those in Venezuela. Excluding the U.S.S.R. deposits, about which very little is known, it is quite clear that the oil sand deposits of the rest of the world are still largely of academic interest, their development might be for local use e.g. Angola, but most of all their develop ment will be restricted by the cost and logistics of the mining and conversion operation. The major accumulations of oil sands are restricted geographically to 8 countries of the world. Over 95 per cent of the known in-place oil volumes occur in Canada, Venezuela and with a lesser, but nevertheless substantial amount, in the U.S.A. The oil sand deposits of the world have been described as belonging to two types: in-situ deposits which result from breaching and exposure of an existing oil trap, and migrated deposits resulting from accumulation of migrat ing oil at outcrop. There are, inevitably, gradations and combinations of these two types of deposits. Migrated deposits are usually associated with active oil seeps. The chemical constituents of the source material and source environment are thought by some to influence the exact characteristics of the crude others believe that the crude characteristics are shaped by the bacterial action. The deposits occur in a variety of different entrap ments (Figure 2). Notwithstanding this variety, some authors recognize a broad pattern to the deposit en trapment. They believe that stratigraphic trapping, fre quently associated with gentle regional structure is a major factor. Kappeler (1967) notes a pattern which he claims is identified in 99 per cent of the large oil sand deposits. They all occur along the rim of major sedimen tary basins and near the edge of pre-Cambrian shields in beds either: 1) transgressing over an ancient relief at the edge of the shield like those in Canada, or 2) directly overlapping on the ancient basement as in Venezuela, West Africa and Madagascar. Most significant is the occurrence of most of the major oil sand deposits in fluviatile and deltaic environments. In the few cases where they are considered of marine origin, it is proposed that even these may be shore-line fades' underlain or overlain by fluviatile and deltaic deposits. The in-place oil volumes quoted on the illustrations to this paper are not intended as the basis of a reserve inventory. They must be regarded as orders of magni tude. Nowhere will you see reference to estimates of recoverable reserve, because any such estimate is far too cost-, time-, and technology-dependent to make sense unless referred to a particular area or method of recovery. Let us then examine some of these major deposits which occur around the world with the exception of the Alberta and Orinoco oil sands which are covered by specific papers in this conference. The abbreviations used on the diagrams are as follows: RE Reserve Estimate A Area T Thickness of deposit OT Overburden Thickness BS Bitumen Saturation %S % Sulphur Conversion to metric: 1 ft 0.304 m. 1 mi 1.609 km lbbl 0.1636m3.