Popular Science Monthly/Volume 50/January 1897/Petroleum, Asphalt, and Bitumen
|PETROLEUM, ASPHALT, AND BITUMEN.|
By M. A. JACCARD.
PETROLEUM, asphalt, and bitumen may be regarded as so related to one another, so like in origin and properties, as to be callable of being considered in the same treatise; and we may, therefore, speak properly now of one, now of the other. The oldest known form of natural hydrocarbon was the bitumen which rose to the surface of the Dead Sea, called from that circumstance the Asphaltum Lake. Tradition says that it used to appear on the surface in considerable masses, and was collected by the Arabs and exported to Egypt, where it was used in embalming, and for a few purposes in the arts. The ancients were also acquainted with the liquid form of bitumen, petroleum. Herodotus speaks of the mineral oil of Zante; and other Greek authors mention the springs of Agrigentum, the product of which was burned in lamps, and was known as Sicilian oil. The fire worshipers of Persia erected temples over the burning springs.
Of the use of these substances in the middle ages, and later, we chiefly know that the petroleum springs of Pechelbronn, in the sixteenth century, spontaneously furnished mineral oil in such quantities that the peasants around used it to feed their lamps and grease their carriage wheels. The virtues of the mineral springs of the Jura Mountains were made known in 1712 by a Greek doctor, who pronounced them a treasure that had been unknown from the beginning of the world. Since then new sources have been discovered in all parts of the world, and the uses and applications of petroleum have been immensely and wonderfully extended. The discovery of the American beds of petroleum and the application of industrial processes of distillation to them have been the beginning of a new industry, and of largely extended researches in all countries. Leopold von Buch (1801), who seems to have been the first to discuss the origin of the natural hydrocarbons scientifically, supposed that they were of animal origin. Violet d'Aoust, in 1814, believed them to be of the same origin as the rocks with which they were associated, native eruptive products, the resultants of causes still unknown; and repeated this opinion ten years later. Puvis thought, in 1836, that bitumen penetrated the rocks, according to their porosity, after their formation. Rozet, in 1836, thought that the bitumen of Pyrimont was sublimed from the depths of the globe through a crack that marked the direction of the formation, and was condensed in the porous rocks. Millet, in 1840, thought the same bitumen was derived from the decomposition of accumulations of vegetable matter, and ran down through the rocks. Itier, in 1839, supposed that the bitumens of the Jura were derived from the adjacent bituminous schists, which were full of vegetable fossils. Daubrée, in 1850, believed that the mode of their formation was similar to that of coal, but admitted the possibility of their having been derived from mineral synthesis. These views and the theory of volcanic origin have been reiterated in various modified shapes by other authors. M. Lartet published, in 1866, a valuable study of the geological relations of the bituminous deposits of the region of the Dead Sea.
When the mineral oils of the United States had become a prominent subject of attention, Mr. Leo Lesquereux made an elaborate discussion of them in the form of a letter to Liebig, in 1865, in which he gave his reasons for supposing that they were the products of the decomposition of marine plants. Dr. Sterry Hunt about the same time concluded, from an examination of the petroleum beds of Kentucky, that the oil, or the organic substances from which it was produced, were deposited in the strata where the oil is found contemporaneously with the formation of the rock. Mr. Orton, after a thorough study of the petroleum of the Trenton limestone of Ohio, published his conclusion in 1884, that it was of organic origin—derived from the decomposition of vegetable and animal matter. The supply could not be renewed, and was therefore not inexhaustible. It was probably produced at the ordinary temperature and not by distillation.
Some authors, assuming that these hydrocarbons are derived from the decomposition of organic matter, have tried to imagine the manner of the process, and to distinguish between it and ordinary or putrefactive decomposition.
It is apparent that nothing more than the value of a hypothesis can be attached to these speculations. Nothing indicating sublimation has been observed where the theory supposes it to have taken place; the operation of a natural chemical distillation is not proved by any evidence of such a process having anywhere taken place. The opinions of MM. Daubrée, Lartet, and Coquand, in favor of a chemical origin, being based upon studies of the formations themselves, are regarded as being of more substantial value. These authors, however, are judged to have erred in confounding the original formation of the substances with their appearance where they are found—which, in the view of the author, are two very different affairs.
A bituminous limestone of the Val de Travers, Switzerland, is formed almost wholly of shells, echini, and similar fossils, held together by a calcareous cement. Some of these fossils are only casts, the shell having been absorbed, while the interior, otherwise empty, is partly filled with a viscous bitumen, the quantity of which is proportioned to the size of the shell. In the smaller brachiopods there is only enough to color the inclosing rock a chocolate brown; in the larger ones it forms a lump which is softened by warming. The bituminous limestone of Auvernier is marked by infinitely numerous little cavities, such as are seen in tufas, which are made visible by the presence of a brown substance, the residue of a volatilized bitumen. It also contains casts or impressions of fossilized shells, and in these again are deposits of brown or blackish substance—the organic matter of the mollusk, transformed into bitumen. The cavernous or breccialike rock of Bevais, a few miles south of Auvernier, contains what we might perhaps call glutinous inclusions—cavities corresponding with the internal part of the fossils, colored brown with organic matter. There are also realof viscous bitumen, which liquefy under a slight increase of temperature. A closer examination of the cavity shows that it is the result of the destruction of an astræan polyp. Of the association of petroleum and fossils in the United States, an observation has been recorded by M. Daubrée of petroleum occupying the cavities of fossils—orthoceratites, brachiopods, and corals, as well as porous parts of the rock—in some of the beds of the Ohio Valley; and a statements by MM. Fuchs and Launay, that "a remarkable characteristic of the Canadian oil is the profusion of remains of mollusks and crustaceans, with some traces of marine vegetation, which it contains. This is one of the most serious facts on which an organic origin is attributed to petroleum."
Of the occurrence of these hydrocarbons, including also natural gas, a review of all the theories and evidences leads us to the conclusion that stratified deposits of asphalt, bitumen, and petroleum are found in the different countries of the globe, often associated with salt, gypsum, sulphate of iron, and mineral springs. A considerable number of these deposits are asphaltic or petroleum-bearing basins, of greater or less richness, the working of which requires the boring of wells, or the excavation of galleries permitting a tolerably exact determination of the manner of occurrence of the substances. Nowhere do the works furnish any evidence of the existence of reservoirs or cavities comparable to the caverns of mountainous regions; but everywhere the hydrocarbons are in the state of impregnation or mixture with the rocks in which the workings are made. When they exist in a viscous or solid condition, there is reason for presuming that this state or manner of being is due to particular phenomena of concentration operating at the moment of deposition or after it. The existence of veins or of eruptive beds, ancient or recent, is nowhere established in a certain and indisputable way, but it may be that fissures existing in the rocks have been filled, either from above or laterally, by a posterior displacement.
In attempting to account for the origin of the hydrocarbons, a distinction may be made between two states in which they present themselves, whether on the surface or in the depths of the soil. The initial state, or that of formation, is represented in the stratified beds, where a series of superposed layers is presented. The substance exists, impregnating the rock, and, more rarely, in viscous or solid bituminous masses. The second state, that of alteration or transformation, is met in the beds which have been modified by dislocations, posterior to the solidification of the matters which were deposited in a movable or plastic state. To these dislocations may be attributed the natural petroleum wells which have been known from antiquity, as well as the flows of viscous bitumen which in some regions become solid on exposure to the air.
The slow distillation of marine bodies may be likened, to a certain extent, to the processes of conservation of fossil wood in the bottoms of marshes, peat bogs, etc., under the mud. But while the absence of air is sufficient to assure the preservation of these, the presence of an entirely impermeable envelope is necessary to prevent complete decomposition into volatile gases such as takes place with all animals simply buried under water.
The presence or existence of natural springs of petroleum in the vicinity of mountainous regions is explained, not by dislocations of the ground, but by the fact that the formation of the reliefs is anterior to that of the mineral oil. Instead of regarding these springs as available as guides in researches, they should be regarded as signs of the approaching exhaustion of the arenaceous strata impregnated with oil; these reservoirs not being susceptible, like those of our springs, of being refilled, as the springs are kept full of water by the penetration from the surface.
If, then, we put aside the eruptive process as not well founded, it follows that the search for petroleum should be made with account taken of the conditions of formation of the sedimentary beds, of the extension of the basins in which they are deposited, and of the formations over them.
While the natural hydrocarbons are indisputably found in the sedimentary beds, from the most ancient to those which are still in process of formation, it is nevertheless certain that so far they are most extensive and most generally distributed in the Tertiary formations—excepting always the Silurian and Devonian deposits of North America, which were formed under geophysical conditions which have not yet been recognized in other regions where formations of the same age exist.
In a general way, the signs of the existence of solid, liquid, or gaseous hydrocarbons, exhibited by mud volcanoes, disengagements of natural gas, etc., authorize the presumption of beds near the surface, so that it is useless in such cases to anticipate a favorable result from deep borings.
All the facts noted by students of the natural hydrocarbons may be explained without difficulty under the hypothesis of the organic origin of the natural hydrocarbons, which becomes a complete system, the value of which imposes itself upon every one seeking the solution of the question. All is easy of conception if we suppose a simultaneous precipitation of mineral matters and organic substances derived from the decomposition of animals and plants, when these are found in suitable conditions of the medium and of their own being at the moment they are buried. But all becomes obscure and inexplicable under the hypothesis that these substances are formed in the depths of the globe under the influence of a high temperature and considerable pressure.
- From Le Pétrole, le Bitume et l'Asphalte. Par A. Jaccard, Professeur de Géologie à l'Académie de Neufchâtel. Paris: Félix Alcan, 1895.