|
|
|
REPORT OF WORKING GROUP ON DEFINITIONSA.R. Martinez, Chairman
The Group met during the Conference in order to rationalize three presentations and several discussion points on definitions for heavy crude oil and tar sands. One of the presentations comprised a set of definitions and addendum resulting from a meeting of international experts convened by UNITAR in February 1981. An agreement by consensus on a revision of this set of definitions has been reached by the Working Group. The revised definitions are presented herein for the consideration of the Conference. The definitions as presented may require adaptation in certain circumstances within the basic framework indicated. The Group recommends that these definitions be used by authors of papers submitted to future conferences such as this. A list of the participants in the group is appended to this report.
DEFINITIONS Heavy and extra-heavy crude oils and bitumens are petroleum or petroleum-like liquids or semisolids occurring naturally in porous and fractured media. Bitumen deposits are also called tar sand, oil sand, oil-impregnated rock, bituminous sand. These crude oils and bitumens may be characterized first by viscosity and then by density. In determining the international resource base, viscosity should be used first to differentiate between crude oils, on the one hand, and bitumens, on the other. Subsequently, density should be used to differentiate among extra-heavy crude oils, heavy crude oils, and other crude oils. Bitumens have viscosities greater than 10,000 mPa-s. Crude oils have viscosities less than or equal to 10,000 mPa-s. These viscosities are gas-free as measured and refer enced to original reservoir temperature. Extra-heavy crude oils have densities greater than 1 ,000 kg/m3 (API gravities less than 10 degrees). Heavy crude oils have densities from 934 to 1,000 kg/m3 (API gravities from 20 degrees to 10 degrees) inclusive. These densities (API gravities) are referenced to 15.60 C (60 degrees F) and atmospheric pressure. Crude oils with densities less than 934 kg/m3 (API gravities greater than 20 degrees) may be classified as medium, light, or other crude oils.
COMPOSITION Most heavy and extra-heavy crude oils and bitumens are composed primarily of hydrocarbons. These crude oils and bitumens generally contain only small percentages of vola tile and easily distillable hydrocarbons and frequently contain high percentages of high molecular weight aliphatic and terpenoid hydrocarbons, high percentages of asphaltenes, and significant quantities of oxygen-, nitrogen- and sulfur- bearing compounds. The compositions of heavy and extra-heavy crude oils are variable, and the bitumens from different deposits are not necessarily alike. Heavy and extra-heavy crude oils and bitumens may contain 3 wt. percent or more of sulfur and frequently contain from several hundred to over 2,000 ppm of vanadium. Nickel and molybdenum are also frequently minor components of these crude oils and bitumens.
ORIGIN There is no single explanation for the origin of all heavy and extra-heavy crude oils or of bitumens. There is evidence that light ends have been lost through differential migration or micro biological attack on some medium and light oils while in their reservoirs. It has also been suggested that some heavy and extra-heavy crude oils and bitumens are formed as a result of oxidative processes that occur when oxygen-bearing ground water invades a petroleum-bearing reservoir. Neither of these processes, however, can account for the particularly high content of vanadium or combination of vanadium and sulfur, in some of these crude oils and bitumens.
OCCURRENCES Heavy and extra-heavy crude oil and bitumen occurrences are widespread, being known on all continents save Antarctica, at depths as great as 4,000 metres, in rocks of various lithologies and ages, and under all climatic regimes both on and offshore. Reliability of information on these occurrences has been improving with time in the last few years. In the past such information was scarcely available even with respect to heavy and extra-heavy crude oil deposits dis covered and left "behind the pipe" to produce higher quality reservoirs, plugged and abandoned, or else never tested. The amount of heavy and extra-heavy crude oil and bitumen resources estimated in the world today and recov erable by existing or presently visualized technology exceeds 160 billion metric tons (1,000 billion barrels). Esti mates of the total amount of resources in-place range between 600 and 1,000 billion metric tons (3,800 and 6,100 billion barrels). Current annual world heavy and extra-heavy crude oil and bitumen production is believed to be in excess of 190 million metric tons (1.2 billion barrels) and cumulative production in excess of 7 billion metric tons (45 billion barrels); these estimates are incomplete with respect to the U.S.S.R. and China.
EXPLOITATION Bitumen deposits near the surface may be produced by mining techniques in which the bitumen is extracted from the mined material. For deeply buried heavy and extra-heavy crude oil and bitumen deposits, thermal processes are the predominant recovery methods. These processes, which include steam injection and in-situ combustion, are primarily aimed toward a viscosity reduction and hence increase the mobility of heavy and extra-heavy crude oils and bitumens for production. Novel and improved development strategies (e.g., electric heating, solvent injection, tunneling, horizontal drilling, cogeneration of steam) are currently under active investigation to accelerate the future exploitation of heavy and extra-heavy crude oil and bitumen resources.
WORKING GROUP ON DEFINITIONS: PARTICIPANTS
|