Historical collections of Ohio in two volumes, an encyclopedia of the state, Volume I, Part 11

Author: Howe, Henry, 1816-1893
Publication date: 1907
Publisher: Cincinnati : Published by the state of Ohio
Number of Pages: 1006

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ORIGIN OF PETROLEUM AND GAS.

It is not necessary to consider the origin of natural gas and petroleum separately. They have a common history. They are pro- duced from the same sources, accumulated by similar agencies, and stored in the same reservoirs. In order of formation, petroleum is probably first. It is the more complex in composition and thus nearer to the organic world from which it is derived. Gas is the same substance on the downward road to the simplicity of inorganic compounds. No pro- cess is known by which gas is built up into oil, but the breaking up of petroleum into gaseous products is seen to be constantly go- ing forward in nature, and it is also effected in the large way artificially.

Petroleum never exists free from gas, but it is sometimes asserted that gas is found that has no connection with petroleum. This elaim is probably a mistaken one, and if the dryest gas could be followed throughout its underground reservoirs, it is altogether prob- able that accumulations of oil would be found along the line in every case. There is no horizon known that produces either sub- stance to the entire exclusion of the other.

As already implied, petroleum and gas are derived from the organic world. Both vege- table and animal substances have contributed to the supplies, and these separate sources give different characters to their products, as will be presently shown. There are certain other theories in regard to the origin of petro- leum, it is true, which have been advanced by eminent chemists, but which do not match at all well with the geological facts involved. These last-named theories refer petroleum to peculiar decompositions and recompositions, chiefly of water and carbonic acid, which are supposed to be carried ou at considerable

depths in the earth, where these substances are brought into contact with metallic iron or with the metallic bases of the alkalies at high temperatures. Never were more arti- ficial or unverifiable theories presented for the explanation of natural phenomena, and it is surprising that they should have obtained any currency whatever. Something might be said for them, perhaps, if we had no other possible way of accounting for the facts to which they refer, but when they are compared with the theories of organic origin they have no standing-ground. The truth is, we are constantly manufacturing from animal and vegetable substances in the large way, both gas and oil that are fairly comparable in both chemical and physical characteristics, with the natural products. Further, we find vege- table substances passing by natural processes into petroleum and allied compounds, so that there is no need whatever to invent a strained and fantastic theory based on remote chemi- cal possibilities, in order to cover the ground. These chemical theories teach that the pro- cess of oil and gas formation is a continuous one, and no reason is apparent why stocks may not be maintained from such a source even when they are drawn upon. Perhaps it is this feature that has recommended these theories more than any other. Any doctrine that gives us unwasting supplies of force is sure to be popular as long as it can find the semblance of justification, as witness the hold that the claims for perpetual motion have on the public mind.

The petroleum and gas of shales and sand- stones are in the maiu derived from vegeta- ble matter, and as the principal stocks are found in sandstones, vegetable matter may be said to be the chief source. The oil and gas of limestones are presumably derived from animal matter, inasmuch as the lime- stones themselves are known to be, in the main, a product of animal life.

The vegetation principally employed in this production is of the lower kinds, sea- weeds and other allied groups being al- together the most conspicuous elements. The animal life represented in limestone oil and gas is also of the lower groups. Plants may have been associated also with animal matter in the formation of limestone oil, to some extent.

HOW WAS PETROLEUM FORMED ?

To the question, How were these bodies formed out of organic matter ? there are various answers.

They are most commonly referred to the agency of distillation. Destructive distilla- tion consists in the decomposition of animal or vegetable substances at high temperatures in the absence of air. Gaseous and semi- liquid products are evolved, and a coke or carbon residue remains behind. The " high temperatures " in the definition given above must be understood to cover a considerable range, the lower limit of which may not ex- ceed 400 or 500 degrees F.

Petroleum and gas on the large scale are

'THE GEOGRAPHY AND GEOLOGY OF OHIO.

not the products of destructive distillation. If shales, sandstones, or limestones holding large quantities of organic matter, as they often do, and buried at a considerable depth, should be subjected to volcanic heat in any way, there is no reason to doubt that petro- leum and gas would result from this action. Without question, there are such cases in vol- canic districts, but the regions of great petro- leum production are remarkably free from all igneous intrusions, and from all signs of excessive or abnormal temperatures. All claims for an igncous origin of these substances are emphatically negatived by the condition of the rocks that contain them.

There is a statement of the distillation theory that has attained quite wide accept- ance, which needs to be mentioned here. It is to the effect that these substances, oil and gas, have resulted from what is called "spon- taneous distillation at low temperatures," and, by low temperatures, ordinary temperatures are meant. It does not, however, appear on what facts in nature or upon what artificial processes this claim is based. Destructive distillation is the only process known to science under the name of distillation, which can account for the origin of oil or gas, and this does not go on at ordinary or low tempera- tures. A process that goes on at ordinary temperatures is certainly not destructive dis- tillation. It may be chemical decomposition, but this process has a name and place of its own, and does not need to be masked under a new and misleading designation, such as spontaneous distillation. No help can come to us, therefore, from the adoption of the spontaneous distillation theory.

It seems more probable that these sub- stances result from the primary chemical de- composition of organic substances buried with the forming rocks, and that they are retained as petroleum in the rocks from the date of their formation. It is true that our knowledge of these processes is inadequate, but there are many facts on record that go to show that petroleum formation is not a lost art of nature, but that the work still goes on under favorable conditions. It is very likely true that, as in coal formation, the conditions most favorable for large production no longer occur, but enough remains to show the steps by which the work is done.

The "spontaneous distillation " theory has probably some apparent support in the fact that must be mentioned here, viz. : that where petroleum is stored in a rock, gas may be constantly escaping from it, constituting, in part, the surface indications that we hear so much of in oil fields. The Ohio shale, for example, is a formation that yields along its outcrops oil and gas almost everywhere, but nic recent origin is needed for either. The oil may be part of a primitive store, slowly escaping to the day, and the gas may be con- stantly derived from the partial breaking up of the oil that is held in the shales. The term "spontaneous distillation " might, with a little latitude, be applied to this last-named

stage, but it has nothing to do with the origin of either substance.

While our knowledge of the formation of petroleum is still incomplete and inadequate, the following statements in regard to it are offered as embodying the most probable view :

1. Petroleum is derived from vegetable and animal substances that were deposited in or associated with the forming rocks.

2. Petroleum is not in any sense a product of destructive distillation, but is the result of a peculiar chemical decomposition by whic' the organic matter passes at once into this o1 allied products. It is the result of the pri- mary decomposition of organic matter.

3. The organic matter still contained in the rocks can be converted into gas and oil by destructive distillation, but, so far as we know, in no other way. It is not capable of fur- nishing any new supply of petroleum under normal conditions.

4. Petroleum is, in the main, contem- poraneous with the rocks that contain it. It was formed at or about the time that these strata were deposited.

THE DISTRIBUTION OF PETROLEUM AND GAS.

Contrary to a commonly received opinion, petroleum and gas are very widely distributed and very abundant substances. The drill can scarcely descend for even a few hundred feet at any point in Ohio, without showing the presence of one or both of them. The rocks of the State series can be roughly divided into three great groups-limestones, sand- stones and shales. Petroleum is found abundantly in each of these groups. The percentage is small, but the aggregate is large. It is equally, or at least generally diffused throughout certain strata, while in others it is confined to particular portions or beds. An example of the first case is found in the Ohio shale. The Ohio Shale, Cleve- land-Erie-Huron, of earlier reports, con- sists of a series of homogeneous, fine-grained deposits, black, blue and gray in color, 300 feet thick on their western outcrop in Central Ohio, but more than 1,800 feet thick under cover in Eastern Ohio. This entire forma- tion is petroliferous, as is proved by an ex- amination of drillings that represent the whole section. The black bands are prob- ably most heavily charged. The chemist of the survey, Professor N. W. Lord, finds two-tenths of one per cent. of petroleum, as such, present in these bands, and is certain from the nature of the processes that he was obliged to employ that the entire amount is not reported. But, estimating the percent- age to be but one-tenth of one per cent. in place of two-tenths, and calculating the thick- ness of the shale at its minimum, viz., 300 feet, we find the total stock of petroleum held in the shale to be 1,560,000 bbls. to the square mile, or nearly twice as large amount as has ever been obtained from any square mile of the Pennsylvania fields.

Of the limestones of the State the Water

THE GEOGRAPHY AND GEOLOGY OF OHIO.

lime, or Lower Helderberg limestone, is prob- ably the most heavily and persistently charged with petroleum. Drillings taken from this stratum, at a depth of 400 to 500 feet below the surface in the trial-well lately sunk at Columbus, are found by Professor Lord to have the same amount of free petroleum that the black shale contains, viz., two-tenths of one per cent. The limestone also has the same thickness that is assigned to the shale on its outcrop, viz .. 300 feet. The figures, therefore, duplicated those already given. The total amount of oil from these two sources exceeds 3,000,000 bbls. to the square mile.

All the other great limestones of our series carry petroleum, at least in certain beds. The Clinton limestone is often an oil-bearing rock, and the show of its outcrop has led to the sinking of a number of wells in search of oil, in past years. The Niagara limestone is highly hituminous in places. Asphaltic grains, films and masses constitute as much as 4 or 5 per cent. of its substance at several points in the State. The Corniferous lime- stone is also distinctly hituminous in some of its beds. The limestones of the Cincinnati group also carry a determinable amount of petroleum.

As for sandstones, all know that it is in them that the main stocks of petroleum have thus far been found, but there is good reason to believe that these stocks are not native in the sandstones, but have heen acquired by them subsequent to their formation. This point will be considered further, under an- other head.

MODES OF ACCUMULATION OF PETROLEUM AND GAS.

In the accumulation of petroleum, two stages are to be noted, viz. : a primary and a secondary stage. The first is concerned with the retention of petroleum in the rocks, and might have been with equal propriety treated under the preceding head. The second stage is concerned with the origin and maintenance of the great stocks of oil and high-pressure gas, in which all the value at- tached to these substances lies. Both are connected with the composition of the rock series in which oil and gas are found, and the latter is also greatly affected by the arrange- ment and inclinations of the rock masses, or, in other words, by their structure.

The primary accumulation of petroleum, or its retention in the rocks in a diffused or distributed state, seems to be connected with the composition of the series to a great degree. The great shale formation of Devonian and Subcarboniferous ages that separates the Berea grit from the Devonian limestone, the western edge of which shale formation out- cropping in Central Ohio is know as the Ohio shale (Cleveland, Erie, Huron), is unmis- takably the source of the greatest accumula- tions of oil and gas, so far found, in the country. It holds thus far, as decided, a superiority to all other sources, as the Ap- palachian coal-field does to all other sources

of fossil fuel. The accumulation of petroleum in this great shale formation is no accident. It depends on two factors, viz. : the abun- dance of vegetable matter associated with the shales in their formation, which is attested by the large amount still included in them, and upon the affinity of clay for oil. The last-named point is an important one. Clay has a strong affinity for oil of all sorts, and absorbs it and unites with it whenever the two substances are brought into contact. Professor Joseph Leidy made the interesting observation a number of years since, that the bed of the Schuylkill river in Philadelphia, below the gas works, was covered with an accumulation of the oily matters that are always formed in the process of gas-making. As these substances are lighter than water and float upon its surface naturally, it was at first sight hard to understand how they could have been carried to the river bed, but it was soon learned that the clay of the river water absorbed the oils as they were floating along. and finally sank with them to the river floor. In a similar way we may suppose the primary accumulation of petroleum in the shales to have been in part accomplished. The oil set free hy vegetable decomposition around the shores or beneath the waters of a sargasso sea, would be arrested by the fine-grained clay that was floating in the water, and would have sunk with it to the sea floor, forming this homogeneous shale formation that we are now considering. Sand would have no such collecting power.

The distribution of petroleum through limestone is not as easily explained, but it may be in part dependent on the presence of the same element, viz., clay. In almost all limestones there is a percentage of clay pres- ent, and frequently it rises to a conspicuous amount. Oil is held in both magnesian lime- stones and in true limestones in Ohio. The magnesian limestones are largely in excess in the series of the State, and it so happens that all of the most petroliferous strata are magnesian in composition, but this fact is probably without significance in this connec- tion.

Petroleum distributed through shales or limestones in the low percentages already named, although the total amount held may be large, is of no economic value. Like other forms of mineral wealth, it must be concen- trated by some natural agencies before it can become serviceable in any way. This brings us to consider the secondary accumulation of petroleum already referred to, by means of which all the great stocks have been formed and maintained. This constitutes one of the most important subjects in the entire history of petroleum. The sources of oil and gas are very widespread, as has already been shown, but the concentrated supplies are few and far between. To learn the horizons and locations of these supplies is the condition of most suc- cessful operations in the production of oil and gas, and it is in this field that the most im- portant practical applications of geology to these subjects are to be found.

THE GEOGRAPHY AND GEOLOGY OF OHIO.

OIL GROUPS.

As the experience of the last thirty years has abundantly shown, an oil or gas series always consists of two elements, viz., a porous rock, or reservoir, overlain by a close and fine- grained impervious rock or cover. A third element must always be added to make out the logical series, viz., an underlying or asso- ciated source of oil and gas. It is obvious that the last-named element is first in order and in importance, but for reasons already given in part, and for others that are not hard to find, practically we have less to do with it than with the two former elements. It will be borne in mind that the sources of petroleum are well-nigh universal, and also that they have no economic value, and are therefore seldom penetrated by the drill. The search generally terminates in the reser- voir. The great sources of the Ohio scale are, as already implied, shales and limestones, both more or less bituminous. These sources have done their work wherever large accumu- lation is found, and where no accumulations exist the petroleum occurs, as already shown, in large but valueless stocks distributed through the body of the strata.

THE RESERVOIR.

The reservoirs must be porous rocks. In all of the experience in the great fields of Pennsylvania and New York, the rocks in which the large stocks of oil and gas were found were, without exception, sandstones or conglomerates. To them the driller early gave the name of " oil-sands," and this name is in universal use. The grain and thickness of these sandstones are found to be important factors in their production. Other things being equal, the coarser the grain and the thicker the stratum, the greater is its produc- tion. found to be. Mr. J. F. Carll, of the Pennsylvania Geological Survey, our highest authority in regard to petroleum production, has shown that an oil-sand can hold one-tenth of its bulk of oil, and he believes that it may contain under pressure as much as one-eighth of its bulk. This would give 1} inches of oil to every foot of the oil-sand.

Taking the most productive portions of the latter in the Venango field to be fifteen feet, we find in that district a possible capacity of 9,600,000 barrels per square mile, an amount, it is needless to say, vastly in excess of any production ever known. - " Second Pennsyl- vania Survey, Oil Regions," III., pp. 252- 53.

The driller places great reliance on the oil- sand, and learns to draw conclusions and make forecasts from its character more than from any other single element that he en- counters.

Within the last few years we have found in Ohio a reservoir of high-pressure gas and large oil-wells, in a rock of altogether differ- ent character from the oil-rocks already de- seribed. The new oil- and gas-rock of North- western Ohio is a magnesian limestone or dolomite, of a good degree of purity. It is

as porous, apparently, as the sandstones and conglomerates of the Pennsylvania series, this character being due in the limestone to the imperfect interlocking of the dolomite crystals. The dolomite constitutes but a small portion of the Trenton limestone in which it is found. The normal character of this great sheet is that of a true carbonate of lime, but it appears that, in a limited terri- tory, the upper portions of the stratum have been transformed into dolomite. The trans- formation seldom extends more than a seore or two of feet below the surface, and is often confined to five or ten feet. Sometimes a cap of true limestone, five or ten feet in thick- ness, overlies the dolomite, and sometimes the latter occurs in two or more sheets, sepa- rated from each other by the normal rock. The Trenton limestone is not itself a porous or reservoir roek in any sense of the word. It is only these replaced beds that have this character.

Besides sandstones and limestones, shales also serve to a small extent as receptaeles of accumulated oil and gas in Ohio. The char- acter of the containing rock in these cases is not well known. Generally, the gas is of light pressure, but it is a fairly persistent supply that is found in these rocks. The belt of shales along the shore of Lake Erie gives the examples of this sort of accumula- tion and supply. These shales, where pro- ductive of gas, are found to consist of hard and light-colored bands, interstratified with dark bands, the gas appearing to be found when the harder bands are penetrated. The production of oil from these sources is always small, but, as already stated, fair amounts of gas are sometimes derived from them.

Petroleum and gas are not the only sub- stances that are found in these reservoirs. Salt-water is almost an invariable accompani- ment of both. The oil-rocks are salt-rocks as well, in some parts of their extent. The dis- tribution of these three substances in the same stratum is connected with facts of structure, as will presently be shown. These reservoirs have been described as porous of necessity. The porosity insures a large amount of lateral permeability, a fact of great importance in the distribution of these sub- stances. The reservoir is often common for large areas. All the wells in a field may find the same pressure of gas or oil, even though their production may be very unequal.

THE COVER.

Inasmuch as the three elements-source, reservoir, and cover-are all indispensable, it is not necessary to compare their relative im- portance. It is, however, true that the first and second conditions of accumulation are met more frequently than the third. The cover of every productive oil-rock is a large body of fine-grained, impervious clay shale- the finer and more nearly impervious the better. Whenever such a body of shale is found in the Ohio scale, the rock directly underlying, if a sandstone or limestone, is

THE GEOGRAPHY AND GEOLOGY OF OHIO.

found to contain, in some portions, accumu- lations of gas and oil. The stocks may be too small to be valuable, but the presence of the shale cover seems to insure some concentra- tion in these situations. There are three points in the Ohio series of rocks where such shale covers occur, viz., at the surface of the Trenton limestone, where 800 to 1,000 feet of shales and intercalated beds of limestone of the Medina, Hudson river, and Utica epochs are found, at the surface of the Cor- niferous limestone, which is covered by 300 to 1,800 feet of the Ohio shale, and at the surface of the Berea grit, which is overlain by the best cover of the entire series, viz., the close-grained and nearly homogeneous Cuyahoga shale, 300 to 500 feet in thickness. Two of these, the first and the last, constitute the two main horizons of oil and gas in Ohio. The third is not notably productive thus far in Ohio, but it is the source of a small supply in other States.

The composition of an oil-producing series is thus seen to be essential to its functions. The order already pointed out cannot be de- parted from, but there must always be (1) an impervious cover ; (2) a porous reservoir ; and underneath the reservoir, the source is to be found.

STRUCTURE AS AFFECTING OIL AND GAS ACCUMULATION.

But this order of arrangement is not enough in itself to insure any large concentration of oil or gas at any particular place. One other factor must be introduced, viz., structure. The strata which constitute the geological scale of the State nowhere lie, for any consid- erable extent, in horizontal planes. They are all more or less inclined. Sometimes they are bent into low folds or arches, and sometimes, though very rarely, there are abrupt descents and fractures. As a rule the dip, or angle of inclination to the horizon, of Ohio rocks is very small. It is better ex- pressed as a fall of so many feet to the mile, than by angular measurements, which very seldom rise to one degree. Both the rate and the direction of the descent are uniform over large areas. The average dip for impor- tant portions of the State is between twenty and thirty feet; the direction depends, of course, upon the part of the State which is to be considered.

The movements of the strata here referred o have exerted a very important influence on he concentration of oil and gas in the reser- oirs already described. If one of these sand- stone strata, filled with salt-water, oil, and gas, and freely permeable laterally and hori- zontally for even miles at a time, were to be thrown into a system of low folds, what effect would this movement have upon the contents of the stratum ? Would not a separation of gas, oil, and water be sure to follow, the gas finding its way to the summits of the arches, and the salt-water sinking to the bottoms of the troughs? Such a result would be in- evitable under the conditions assumed.

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Historical collections of Ohio in two volumes, an encyclopedia of the state, Volume I, Part 11

Author: Howe, Henry, 1816-1893 Publication date: 1907 Publisher: Cincinnati : Published by the state of Ohio Number of Pages: 1006

Author: Howe, Henry, 1816-1893
Publication date: 1907
Publisher: Cincinnati : Published by the state of Ohio
Number of Pages: 1006