the gas industry. Whether the United States natural-gas reserves are adequate for a somewhat shorter or longer period than the 50-year estimate is relatively immaterial. Fifty years is a short range as compared to any reasonable forecast of future United States industrial activity.

The United States coal industry's place in the power and metallurgical fields must be protected. Coal mining has many problems, financial and otherwise. It must not be set back in its modernization progress which has been a revelation to the entire world. The industry must be kept healthy so that it will be ready to meet any emergency, as has been required on numerous occasions in the past. It must be prepared to take its place in the wide expansion of the chemical industry, which, to a great extent, will be built around coal. Besides, adequate coal production must eventually be available so that the gasification of coal can take the place of the declining production of natural gas. Anything that creates a situation where the United States coal industry will require any form of Government subsidy will place the gas industry in competition with the Government with inevitable chaos in that industry also.

Similarly, the future of the United States metal, industrial minerals and other mining products and industries must be given consideration insofar as their established position as a national asset might be affected by gas storage underground.

Even to the layman, who knows that there are radical seasonal demands for industrial and household fuel, the financial impracticability of building pipelines adequate in size to meet seasonal maximum consumer loads is quite apparent. If this were practiced, there would be great excess capacity to transmit gas in the offpeak seasons. This would undoubtedly cause the gas companies to offer industrial gas at abnormally low rates during such time for use under steam boilers in place of coal and oil in order to utilize their line capacity as nearly as possible to the maximum. Such a "dumping of gas would not only be disastrous to the normal use of other fuels, but would result in an unwarranted waste of our natural resources.

The policy of finding and establishing safe and practical underground gas-storage reservoirs so that pipeline capacity can be utilized to the maximum extent during all of the months of the year without interfering with other industries is most logical and reasonable. It follows, therefore, that such underground gas storage is a "must" not only for the gas companies, but for the utilization economics of all kinds of fuel of the country. To take issue with this fact would be a waste of time and energy.

In addition, it is equally reasonable to be in accord with the economic fact that gas storage, receiving gas from large high-pressure lines, should be located as near as possible to the consumers. The smallest size and number of distribution lines are essential to keep consumer costs at a minimum.

However, Messrs. Max Ball and John A. Vary, oil and gas consultant, Washington, D. C., and chief engineer, Michigan Consolidated Gas Co., respectively, wrote in May 1949:

The storage fields now in use or preparation lie from 0 to 200 miles from the markets to which they are connected. I suspect that a large transmission company or utility could afford, when other conditions favor it, to go as far as 300 miles, perhaps 400, from its market, provided storage and markets were directly connected by pipeline independent of the main transmission line. Storage

located three or four hundred miles back down the main line, and only connected with its markets by the main line, would lose some of its economic advantage. It might not lose all, and might still be worth while, under special circumstances.

The rights granted under the privilege of eminent domain to gas companies, whereby they could condemn coal or other mineral-bearing lands to protect their pipelines and storage reservoirs from subsidence or from upward gas-seepage dangers, can be a very serious matter when it is understood that such pipelines may require that belts of underlying coal and minerals of as much as 1000 feet or more in width may be necessary to protect the pipeline right-of-way from the vertical and lateral subsidence caused by underground mining.

Similarly, since presently known gas-storage reservoirs underlie as much as 100 square miles of overlying strata which may contain coal and other minerals, the possibility that a vast amount of mineral acreage may be condemned to avoid safety hazards to the mineral reserves or to the personnel working in operating mines creates cause for thought concerning the effect of such condemnation on the mining industry's present and future.

For example, in the case of one large storage pool in western Pennsylvania underlying four large metallurgical coal mines, it is conceivable under the broad rights of eminent domain that that gas company might condemn all of these mines which at present produce 26,000 tons of coking coal per day and employ about 3,700 men. The 30 to 60 million dollar value of these mines is relatively small compared to the potential value of gas storage near consuming centers.

It must always be remembered that there is considerable metal mining in eastern United States. Important iron, zinc, and industrial metals occur and are mined in Ohio, eastern Pennsylvania, New Jersey, and in New York. The fact that, in general, easily accessible storage reservoirs occur in exhausted gas or oil sands which in turn are usually in coalfields does not mean that other sands, known or unknown, cannot or will not eventually be utilized for underground gas storage. It is true that such sands may not be discovered at this time, but increasing storage demands can create the desire to find them, especially if they are near large consumer areas.

The most desirable pools, from the standpoint of the gas industry alone, are those having the greatest storage capacity. Capacity, however, varies with the ability of the sands to take gas and with the pressure which the impermeable strata seal will resist. Moreover, capacity may become a secondary consideration when evaluated with the ability of the storage sand to take and give up gas quickly. This is what is known as the injection and withdrawal rate of the pool.

In order to determine each or all of the above requirements, substantial test periods must be carried out. All of the known gas wells penetrating a given reservoir must be reconditioned by redrilling and recasing to insure that such old openings are gastight above the reservoir. In many cases the work required to do this job properly is much more expensive than the drilling of new wells. All or most of these reconditioned wells are then equipped with valves and other fittings for injection and withdrawal of the gas and connected with central pumping stations.

The known wells having been so reconditioned, gas is then forced into the potential reservoir at predetermined and planned variable. pressures. The testing of withdrawal rate can then be started, as

suming there is a market at that time for the gas. The operation can then be repeated at increasing pressures and the cycle continued.

The determination of what residual gas may have been lying in the pool and becomes a part of the total gas in storage and the determination of what new gas may migrate or be lost as "cushion" gas cannot be ascertained with mathematical accuracy. Most important is the possibility that storage pressure may exceed the strength of the seal within or without any given estimated pool perimeter. Leakage may then come from natural structural crevices, from manmade crevices, especially from abandoned and uncharted wells, and from improperly plugged or reconditioned wells.

The need for speed in testing storage reservoirs, coupled with_the rapid reconditioning of old wells, much of it occurring as it did during the shortage of materials resulting from the Korean war, was not conducive to the use of first-class casing materials and auxiliary equipment in the rehabilitation of such old wells. As a result of these conditions, some of these installations undoubtedly are weak structurally of themselves and, perhaps more important, may not be able to withstand future ground movements or corrosive action of underground waters.

These are hazards to the future stability and dependability of the gas storage pools from the gas companies' viewpoint. To coal companies whose property is adjacent and exposed to gas leakage accidents, it is a matter of grave and deep concern.

The inability to define storage pool limits with any degree of certainty and the chance of porous sand "fingers" extending out from what seems to be the best defined perimeter is perhaps one of the greatest risks and causes of concern. This possibility of long, porous sand fingers, due to the conditions of the storage sand and to the migratory characteristics of the gas, whether caused by increasing gas pool pressure, prevents both the gas company and the coal operators concerned from ever saying positively that conditions are stabilized and that all possible storage pool leaks have been eliminated.

As customer demand increases, the temptation of the gas companies to increase pressures, even beyond the original discovery rock pressures, and to expand the perimeters of the storage pools, is an ever present challenge. The study of the pool perimeter pressures creates a situation requiring the best engineering imagination and foresight to attempt to predict both the amount and the direction of pool expansion. This is a cause of great concern to the coal companies, because it is a well-recognized fact that, although gas storage reservoirs may be of limited areas under certain storage pressures due to resistance of the sands, greater pressure will over come the resistance and will spread the pool over far larger areas. In fact, gas storage reservoirs which are now isolated from each other under existing pressures may become united under higher pressures.

It is this situation which frightens coal companies carrying on mining activities within the area of the supposed pool perimeters which may never exactly be defined and which are certainly potentially expanding by physical changes underground. Furthermore, it is not considered to be good storage practice to recondition wells over a large area prior to test injection.

The relationship of the Pratt pool to four overlying active mines in Greene County, Pa., is an outstanding example of storage reservoirs'

changing size and boundaries. The Equitable Gas Co. themselves have defined progressively changing perimeters of this pool. These different perimeters reflect the results obtained from their reconditioning program over a period and presumably from their recording of the pressures encountered on all of the reconditioned wells.

It is quite obvious that the principal perimeter changes are more pronounced in those areas where the most recent well reconditioning has been done. This is an indication of the lag of well conditioning practice behind underground gas migration.

Risks in underground gas storage peculiar to the gas companies only may be listed as follows:

1. Unrecoverable cushion-gas requirements being much greater than residual strata gas yield from a pressurized sand. It is a distinct possibility that many storage sands will hold an appreciable amount of gas which would require an uneconomical suction to recover. Such gas will be lost. Besides, the expanding area of storage pools due to increased pressure, in the manner referred to above, may require the storage of such an enormous quantity of unrecoverable cushion gas as to render a given storage reservoir impractical.

2. A decreasing withdrawal rate as the storage pool is drained. If the capacity of existing pumping installations to withdraw sufficient gas during peak demand periods is lowered to an uneconomical point, the amount of lost cushion gas will be increased.

3. Public liability caused by pool gas storage accident possibilities to others. This liability includes the hazard to mines through which the storage wells may pass.

Risks in underground gas storage peculiar to mining companies are as follows:

1. The inadequacy of pillars left around gas wells, although these pillars were considered fully adequate to protect the mine workings against the almost negligible pressure then remaining in the original gas. Such pillars, many of which are in inaccesible worked-out portions of a mine, may be either insufficient in size to stand storage pressures or may have partially or entirely crushed out due to the complete extraction of adjacent areas.

2. A mining operation may be jeopardized by the negligence of or difficult gas sealing problems of its adjoining mining neighbors. 3. Gas companies' inability to forecast or foresee changes in pressures or perimeters in gas storage. There have been many instances to date of noncooperation in this respect.

More important than the above-mentioned risks which are peculiar to each of the parties, are what might be called mutual risks, as follows: 1. Uncharted wells which may be punctured by mining operations. 2. Vertical plus horizontal gas leaks in original strata.

3. Vertical plus horizontal gas leaks in original strata disturbed by well drilling or mining.

4. Reconditioned well gas leakage caused by subsequent subsidence from mining.

5. Inferior plugging of wells which proved adequate for low-pressure leaks but inadequate for high-pressure leaks.

6. The inability to define storage pool limits with any degree of accuracy and day by day.

7. Rock strata damage around gas wells caused by the original drilling or "shooting" of wells, or caused by reconditioning.

S. Future corrosive action on casings by underground waters. 9. Unworkmanlike reconditioning of wells.

Coal companies are continually facing the possibility that all underground employees may be killed by gas explosions or fires due to the storage of gas beneath their mines, as well as the possibility of loss of their entire investment in real and personal property by such occurrences. The irony of any such occurrence is that, in most instances at least, the gas storage hazards have been introduced by the gas companies long after the coal mining operations have been started and without the consent of the coal companies.

There is no known practical mining ventilation precaution that could take care of gas entering mine workings in large quantities, especially under high pressures. For example, if gas at 100 pounds per square inch were to enter a mine through a 1-inch opening in the well casing, it would be at a rate of approximately 1.000 cubic feet per minute. Such a quantity of gas would require 100.000 cubic feet of fresh air per minute to dilute it to 1 percent gas content. This is far in excess of the amount of air which can be passed over any particular point in any one air split. If the gas were to enter through such an opening at 600 pounds per square inch pressure, approximately 6,500 cubic feet would be admitted into the mine and this would require 650,000 cubic feet of fresh air per minute to dilute it. This is many times the amount of air that has ever been known to be available at any one point in a mine. This 600 pounds per square inch gas pressure, however, is about the present average gas storage pool pressure in the southwestern Pennsylvania area under consideration.

Explosive gas in limited quantities is present in most of the coal mines in the area discussed in this paper. Mine disasters in southwestern Pennsylvania and in West Virginia since 1902 from explosions in which 100 or more men were killed are as follows: January 25, 1904, Cheswick, Pa., 179; December 6, 1907, Monongah, W. Va., 361; December 19, 1907. Jacobs Creek. Pa., 239; November 28, 1908, Marianna, Pa., 154; April 28, 1914, Eccles, W. Va., 181; March 2, 1915, Layland, W. Va., 112: April 28, 1924, Benwood, W. Va., 119; and May 19, 1928, Mather, Pa., 195.

There is a long list of other explosions in which less than 100 men were killed. During the same period, an average of 150 men were killed in 16 major mine disasters in other locations in the United States.

While none of the above major coal-mine disasters were officially attributed to pipeline or gas storage, it has not been proven conclusively that some of these catastrophies were not initiated by the ignition of gas leaking from gas wells. They are listed here to point out that explosive gas, confined in the corridors of coal mines in the presence of explosive coal dust, can cause, and too frequently has caused, terrible catastrophies.

As to the number of times coal-mine operations have cut into abandoned and uncharged gas wells, the writer has found that most coalmining men who have spent any time in the industry can report a number of such instances. Without exception, State and Federal mine inspectors can tell of many such instances in the areas under their jurisdiction. Fortunately, none of these occurrences have been in connection with high-pressure wells or storage pools.