Historical collections of Ohio in two volumes, an encyclopedia of the state, Volume I, Part 12

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

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The summits of the folds are called anti-

clinals, and the troughs synclinals. The lines of direction of the anticlinals are called their axes. The influence of these facts of structure on gas and oil accumulation has been long recognized, or at least asserted, but there is not full agreement as to the part that it plays in the great fields among the geolo- gists who have given most study to the sub- jects.

The facts that have come to light in the recent investigations of these subjects in Ohio seem to show the paramount influence of structure upon oil and gas accumulation. In the old fields, and in the new alike, irregu- larities of dip, involving change of direction, suspension, or unusual increase, have been found connected with the large production of both oil and gas in every instance where careful examination has been made. The composition of the series involved is identical for many thousand square miles, but so long as uniformity of dip is maintained, there is no valuable accumulation. As soon, how- ever, as this uniformity is broken in upon, the valuable stocks of gas and oil come to light.

The "belt lines," in which the practical oil-well driller and operator of the main field puts so much confidence, so far as they stand for facts in nature, are probably structural lines. A map of the various centres of petro- leum in the old field shows that they all ex- tend in the northeasterly course which the main structural features of this part of the continent follow. The driller believes fortune to lie in the 45° or 223 line which leads out in a northeast or southwest direction from each centre of production. Experience justifies, to a certain extent, his confidence. The pro- ductive gas territory upon which Pittsburg now depends is limited to the summits of a few well-marked anticlinals, which all have a northeasterly trend. In regard to the latter, question can scarcely be raised. The pre- dominant influence of structure is obvious. It seems probable that a careful enough system of measurements will show like lines of modi- fied dip to traverse the great oil fields of Pennsylvania and New York.

The occurrence of gas and oil in almost all rocks that have a heavy shale cover would seem to result from exchanges affected by gravity. The oil is associated with salt- water in the stratum that contains it. There would be a constant tendency for the oil to reach a higher level at the expense of the water. It ascends through all the substance of the rock until it reaches the impervious roof, where it is gradually concentrated. On the same principle, the separation of the gas from the oil is effected.

Some of the points that have been made under this head may be briefly restated, as follows :

1. Clay is largely connected with the pri- mary accumulation of petroleum. The natural affinity that it has for substances of this class would lead to its combination with them wherever found. The great shale formation of Eastern Ohio, New York and Pennsyl-

THE GEOGRAPHY AND GEOLOGY OF OHIO.

vania is the main source of the petroleum and gas of these regions. Clay does its work in this regard by reason of its chemical con- stitution.

2. As elay is the main agent in the primary accumulation of petroleum, sand takes a sim- ilar place in its secondary accumulation, or its concentration in valuable stocks. It does this by virtue of its physical character. A sand- stone is a porous rock. Such sandstones as are found overlying or imbedded in the great shale formation are sure to become recepta- les of oil.

3. Clay has another office in this connection to perform, and this office is dependent on its physical character. The sandstone stratum last described would become a receptacle of oil in any case, but if roofed with a sufficient thickness of elay shale by which its contents could be sealed and preserved, it would be- came a reservoir of oil or gas. All of the stocks of the old fields are held in sandstone or conglomerate reservoirs.

4. Limestone has been found, more clearly in Ohio, perhaps, than elsewhere, to replace sandstone in oil accumulation. All the phe- nomena of high-pressure stocks of oil and gas have recently been found in the Trenton limestone of Northern Ohio, but the pres- ence and office of the shale cover are seen to be the same here as in the other fields. The term limestone in this connection is used with due care and precision. It is limestone, not "oil-sand" in the limestone, that contains Findlay gas and Lima oil. Pure magnesian limestone is the driller's "oil-sand" in these fields.

5. Widely diffused as are oil and gas in the paleozoie rocks of Ohio and adjacent States, so wide that the distribution of them may, without error, be styled universal, and widely extended as are the series of rocks that afford in their composition and relations the proper conditions for storage, it is still seen that their accumulation in profitable quantity depends on what might be called geological accidents. It is only or mainly along lines of structural disturbance that the great stocks are found.

THE ROCK PRESSURE OF GAS.

The facts pertaining to the closed pressure of great gas-wells are among the most striking in the whole range of mining enterprise. To be appreciated, a high-pressure gas-well must be seen and heard. The gas issues from it with a velocity twice as great as that of a rullet when it leaves a rifle. Sets of drilling- tools, nearly 100 feet long, and weighing 2,000 pounds, are lifted out of a well 1,000 or 7,500 feet deep and thrown high into the air. The noise with which the gas escapes is literally deafening, exposure to it often re- sulting in partial loss of hearing on the part of those engaged about the well.

What is it that originates this indescribable force ?

One answer is, that the rock-pressure is derived from the expansive nature of the gas. Solid or liquid materials in the reser- voir are supposed to be converted into gas as

water is converted into steam. The resulting gas occupies many times more space than the bodies from which it was derived, and in seeking to obtain this space it exerts the pressure which we note.

This view has, no doubt, elements of truth in it, even though it fails to furnish a full ex- planation. For the pressure of shale-gas, it may be that no other force is required. But the theory is incapable of verification, and we are not able to advance a great ways beyond the statement of it. Some objections to it will also appear in connection with facts that are presently to be stated.

The second explanation that is offered is, without doubt, more generally accepted than any other by those who have begun to think upon the question at all.

This theory is to the effect that the weight . of the superincumbent rocks is the cause of the high pressure of gas in the reservoirs. In other words, the term rock-pressure is con- sidered to be descriptive of a cause as well as of a fact. That a column of rock, 1,000 or 1,500 feet deep, has great weight, is obvious. It is assumed that this weight, whatever it is, is available in driving accumulations of gas out of rocks that contain them, whenever communication is opened between the deeply- buried reservoir and the surface.

Is this assumption valid ? Can the weight of the overlying rock work in this way ?

Not unless there is freedom of motion on the part of the constituents of the rock, or, in other words, unless the rock has lost its cohesion and is in a crushed state. If the rock retains its solidity, it can exert no more pressure on the gas that is held in the spaces between its grains than the walls of a cavern would exert on a stream of water flowing through it. Professor Lesley has discussed this theory with more elaboration and detail than any other geologist, and has shown its entirely untenable character. (Annual Re- port Penna. Survey, 1885.)

The claim that the Berea grit or the Trenton limestone, where they are, respectively, oil or gas-rocks, exists in a crushed or comminuted state, is negatived by every fact that we can obtain that bears upon the subject. The claim is a preposterous one, but without this condi- tion the theory fails.

The third theory advanced to account for the rock-pressure of gas stands on a different basis from those already named. It appeals to water-pressure in the oil and gas-rock, as the cause of the flow of both these substances, and in this reference, it direets us to princi- ciples and facts of familiar experience and every-day use. Every one is acquainted with the phenomena and explanation of artesian wells. By this theory gas and oil wells are made artesian in their flow. In the porous rock that contains them there is always, out- side of the productive fields, a body of water, and, in almost every instance, salt-water. This water occupies the rock as it rises to-day in its nearest outcrops. Communicating there with surface water or with rainfall, a head of press- ure is given to the gas and oil that are held

THE GEOGRAPHY AND GEOLOGY OF OHIO.

in the traps formed by the anticlinals or ter- races into which the stratum had been thrown. The amount of pressure would thus depend on the height to which the water column is raised, in case continuous porosity of the stratum can be assumed. Defects in regard to porosity would abate from the total press- ure on the oil or gas.

This, in short, is the third and last of the explanations offered of the rock-pressure of natural gas. There seems little reason to doubt that it is along this line that the true explanation is to be found, though it is too early to claim that a full account can now be given of all the facts involved.

One of the significant elements in the case is the salt-water that surrounds every oil and gas-field. When the drill descends into this outside territory, salt-water promptly rises in the well to the surface, or to a given depth below the surface. Sometimes, indeed, it overflows. Why does the salt-water rise ?

What other cause can be suggested than pressure from behind? The rise must be artesian. But just beyond the salt-water, on a slightly higher level of the rock, lies the oil pool. When that is reached by the drill, the oil flows out from the well. Will not the same cause that we found in active and un- mistakable operation in the adjacent salt- water territory explain the flow of the oil from the second well? Is not this also ar- tesian ?

In like manner, the pressure of the gas that is confined within the highest levels of the same porous rock can be explained, and thus one familiar cause that is demon- strably present in the field is made to account for the varied phenomena presented.

With the exhaustion of a gas-field or oil- field, these substances are followed up and replaced by salt-water. This is the common fate of gas and oil wells, the death to which they all seem to be appointed.

Certain obvious inferences follow the ac- ceptance of this explanation :

1. The supplies of gas and oil are seen to be definitely limited by this theory of rock pressure. If a salt-water column is the pro- pelling force, it is idle to speculate on con- stantly renewed supplies. The water advances as the gas or oil is withdrawn, and the closing stage of the oil-rock is, as already pointed out, a salt-water rock.

2. Other things being equal, the rock-press- ure will be greatest in the deepest wells. The deeper the well, the longer the water column.

3. Other things being equal, the rock- pressure will be greatest in districts the gas or oil-rock of which rises highest above the sea in its outcrops. The 750 1bs. of reck- pressure in Pennsylvania gas wells, as con- trasted with the 400 1bs. pressure of Findlay wells, can be accounted for on this principle.

4. The rock-pressure of gas may be con- tinued with unabated force until the end of production is at hand. Maintenance of pres- sure is no proof of renewal of supply. The last thousand feet will come out of a gas-

holder with as much force as the first thou sand feet.

5. Where both oil and gas are found in a single field, the first sign of approaching failure will be the invasion of the gas-rock by oil, or of the oil-rock by salt-water.

SOURCES OF GAS AND OIL IN THE OHIO SCALE.

There are known at the present time four utilizable sources of gas and oil among the strata that underlie Ohio. They are as fol. lows, named in descending order :

1. The Berea grit in Eastern Ohio.

2. The Ohio shale in Northern and Central Ohio.

3. The Clinton limestone in Sandusky, Wood, Hancock and Fairfield counties.

4. The Trenton limestone in Northwestern Ohio.

The Berea grit yields high-pressure gas and large stocks of oil under favorable circum- stances, but these circumstances do not often recur. This stratum is doing but very little in supplying to the people of the State either gas or oil at the present time. Outside of Ohio in Western Pennsylvania it is found to be one of the most important repositories of this stored power that has been discovered in that highly favored territory.

The Ohio shale as a source of gas has already been briefly characterized in the account of this formation given on a previous page. It yields low-pressure Igas in small amount at many places, but can never be made a source of large supply.

The two formations next to be named have special interest for us from the fact that their petroliferous character on the large scale was first demonstrated in Ohio. The first of them, indeed, has never been found to be an oil or gas rock elsewhere. It has not yet been proved to be a reservoir of any great value in Ohio, but moderate supplies of gas have been for some time derived from it in Fremont and in adjacent territory of North- ern Ohio. In Lancaster, however, in South- ern Ohio, the largest promise of the rock has recently been found. Wells drilled to the Clinton limestone, which is reached at a depth of 2,000 feet, have yielded as much as 1,000,000 cubic feet a day when first struck. The initial rock-pressure is high, viz., 700 pounds to the square inch. It is too early to draw safe conclusions as to the value of this discovery. All turns on the life of the wells. On account of their depth the drilling and casing are expensive. A well cannot be com. pleted for less than $3,500 to $4,000. The facts at present in hand seem to betoken a short duration for the supply. A large amount of money is sure to be spent in the new field that the experience of Lancaster has brought to light.

It remains to describe in few words the re- markable discovery of gas and oil in the Trenton limestone that was made at Findlay in November, 1884.

The entire history of the discovery and ox- ploitation of petroleum in this country has

THE GEOGRAPHY AND GEOLOGY OF OHIO.

been full of surprises, both to the practical men engaged in the work and to the geolo- gists who have studied the facts as they have been brought to light, but no previous chap- ter of the history has proved as strange and well-nigh incredible as the discovery and development which are now .to be de- scribed.

No fact in this line could be more uncx- pected than that any notable supplies of petroleum or gas should be furnished by the Trenton limestone, which is widely known as a massive, compact and fossiliferous lime- stone of Lower Silurian age and of wide ex- tent, constituting in fact one of the great foundations of the continent. But when re- quired to believe that certain phases of this Trenton limestone make one of the great oil- rocks of our geological scale, one which pro- duces from single wells 5,000 barrels of oil, or 15,000,000 cubic feet of inflammable gas in a day, it is hard to prevent our surprise from passing into incredulity.

Surface indications of a sulphuretted and inflammable gas, escaping from the rocky floor of the village of Findlay, have been known since the country was first settled. The gas had, in fact, been utilized in a small way, viz., in lighting a single residence for more than forty years, but in 1884 the influ- ence of Pittsburg had made itself felt through much of Ohio and drilling was begun here. At a depth of 1,100 feet a re- spectable flow of gas was secured. The suc- cess of this well was the first step in by far the most remarkable development that has ever taken place in the geology of Ohio.

It was more than a year before a great gas well was discovered in Findlay, but the Karg well, which was completed in January, 1886, fully deserves this name. Its daily yield when first opened was uot less than 14,000,000 cubic feet.

The discovery of oil followed that of gas Dy a short interval, but the prolific character of the new rock was not established till the latter half of 1886.

The rapid extension of productive territory and its equally rapid limitations, the develop- ment of several distinct centres, as Bowling Green, Lima and St. Mary's, the great specu- lative excitement that broke out when the good fortune of the new gas-field began to be appreciated by manufacturers and investors, and the wonderful developments that have since taken place in the line of manufactur- ing industries, cannot be even touched upon in this connection. The salient points in the geology of the new fields are brought out in the summary that follows. The discovery comes from an unexpected quarter, viz., from the "black swamp" of old time of North- western Ohio. Under its broad and level expanses a few hundred square miles have been found distributed through portions of five counties, within which are contained fountains of oil and reservoirs of gas of infinitely more value than any like accumula- tions hitherto discovered iu the State, and fully deserving a place among the most

valued repositories of these substances in any quarter of the world.

The leading facts pertaining to the field can be summarized as follows :

1. In fourteen of the northwestern counties of Ohio (and like conditions prevail in con- tiguous territory in Indiana), the upper beds of the Trenton limestone, which lie from 1,000 to 2,000 feet below the surface, have a chemical composition different from that which generally characterizes this great stratum. They are here found as dolomite or magnesian limestone instead of being, as usual, true carbonate of lime. Their per- centage of lime, in other words, ranges be- tween 50 and 60 per cent. instead of between 80 and 90 per cent., as in the formation at large. These dolomites of Northwestern Ohio are mainly quite free from silicious impurities. The dolomitic composition seems to have resulted from an alteration of a true limestone. At least the occasional masses of true limestones charged with fossils, that are found on the horizon of and surrounded by the dolomite, are best explained on this sup- position. In the change which has been endured, the fossils which the original limestones contained appear to have been for the most part discharged or rendered obscure, as is usual in this metamorphosis. The crystalline character of the dolomite is often very marked, and there results from it a peculiarly open or porous structure. Its storage capacity is much greater than that of ordinary oil sandstones and conglomerates, so far at least as pores visible to the unaided eye are concerned. The change usually ex- tends for ten to thirty feet below the surface of the formation. In some cases, however, sheets of porous dolomite are found as low as fifty feet and very rarely as low as 100 feet below the surface.

The area occupied by this dolomitic phase of the Trenton limestone in Ohio has already been indicated. The eastern and the south- ern boundaries pass through Lucas, Wood, Hancock, Allen, Auglaize and Mercer coun- ties. It is possible that the line crosses some parts of Ottawa, Wyandot and Hardin coun- ties.

There is good reason to believe that this phase extends far to the northward and west- ward, outside of the State limits to which it has here been traced. We know that the Trenton limestone is a dolomite when it pitches rapidly down from the northern boundary of Ohio to make the low-lying floor of the Michigan coal basin, and we also know that it is a dolomite when it rises from under that basin as a surface rock of the northern penin- sula. In like manner it is a dolomite when it leaves the western boundary of the State under deep cover, and it is a dolomite when it reaches the surface once more in the Galena district of Illinois and Wisconsin.

South of the line laid down in Ohio there has not thus far been found a trace of the porous dolomite on which the oil of Lima and the gas of Findlay depend. The change is seen to be taking place in Shelby and

THE GEOGRAPHY AND GEOLOGY OF OHIO.

Logan counties, but beyond them the Tren- ton limestone is invariably found with a per- centage of more than 75 per cent. of car- bonate of lime, and rarely with less than 10 per cent. of silicious impurities. It is this last element, with but little doubt, that has resisted the dolomitization of the stratum throughout the southwestern quarter of the State and in all contiguous territory.

To the eastward of the line laid down in Northern Ohio, a less definite boundary is to be looked for. It is certain that small areas of porous dolomite are found beyond the line here recognized as the termination of the Findlay phase of the Trenton limestone.

Within the limits named, the limestone of course has a considerable variety of grain and texture, but all of the analyses obtained show the stratum to be in the main a dolomite. As already stated there are occasional patches ar islands of true limestone in this sea of dolomite.

2. A porous rock, buried 1,000 to 2,000 feet below the surface of Northwestern Ohio, will not be found empty. Nature abhors a vacuum. With what will its pores be filled ? Mainly with salt-water of peculiar composi- tion, possibly representing the brine of the ancient seas in which the limestone was laid down. Ninety-nine-hundredths, or perhaps nine hundred and ninety-nine-thousandths of the limestone will be thus occupied. The remaining hundredth or thousandth will be filled with the petroleum and gas which have, in the long course of the ages that have passed, been gathered from a wide and gen- eral distribution through the water into cer- tain favored portions of the great limestone sheet.

3. This salt-water will be held under arte- stan pressure. The porous limestone con- taining it rises to-day in Michigan and Illinois, communicating there with surface waters. The pressure of this head of water will be felt through every portion of the porous rock, and when the stratum is pierced by the drill in the areas that are thus occu- pied, the salt-water will rise with more or less promptness, depending on the varying degrees of porosity in the rock. The height to which the water will rise will seem to vary in wells, by reason of the different elevations of the locations at which they are drilled, but with reference to sea-level the water columns will be found to closely agree.

The same artesian pressure accounts for the force with which oil and gas escape when their limited reservoirs in the porous rock are tapped by the drill.

4. The accumulations of oil and gas in the porous rock depends altogether upon the attraction of gravitation. The lighter por- tions of the contents of the porous rock, viz., oil and gas, are forced by gravitation into the highest levels that are open to them. Every- thing turns on the relief of the Trenton lime- stone. The gas and oil are gathered in the arches of the limestone, if such they are. In default of arches the high-lying terraces are made to serve the same purpose, but the one

indispensable element and condition of all accumulation is relief. A uniform and monotonous descent of the strata is fatal to accumulation of oil and gas where everything else is favorable. The sharper the boundaries of the relief, the more efficient does it be- come. Absolute elevation is not essential ; all that is required is a change of level in the porous rock. Each division of the field has its own dead line or salt-water line. Salt- water reigns universal in the Findlay field 500 feet below sea-level, except where some minor local wrinkle may give a small and short- lived accumulation of oil or gas. In the Lima field the salt-water line has risen to 400 feet below tide ; in the St. Mary's field to 300 feet below tide, and in the Indiana field to 100 feet below tide. These figures stand in every case for the lower limit of production, with the possible minor exceptions already noted. The rock-pressure of the gas de- creases to the westward in proportion to this decreasing head of water-pressure.

The large accumulations are derived from the large terraces. The Findlay terrace, foi example, consists of a very flat-lying tract, ten or twelve miles across in an east and west line, from which the connected areas of the Trenton limestone slope on every side, and to which, therefore, they are necessarily tribu- tary. The gas terrace of Indiana is, by far, the largest of these several subdivisions of the field. The minor elevations of Oak Harbor, Tiffin and Bryan, for example, give rise to the local supplies of gas or oil in these districts respectively.

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Historical collections of Ohio in two volumes, an encyclopedia of the state, Volume I, Part 12

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