actual expansion of gas in lowering the pressure from 150 pounds down to less than 10 pounds would be about 6 per cent greater than that given by literal application of the law. This has the practical effect of making leakage in main lines and natural gas distributing plants sometimes seem considerably less than it actually is, due to failure to recognize that in expanding from high pressure to low the gas actually increases in volume more than the exact literal application of the law would give.1 EFFECT OF TEMPERATURE ON GAS VOLUME, KNOWN AS CHARLES' LAW. "The volume of a given mass of any gas under constant pressure increases from the freezing point by a constant fraction of its volume at zero." This starts from the absolute zero of the gas, which is 492° F. below freezing, as shown at the right. In other words, the gas will expand 1/492 of its volume at 32° F. for each degree Fahrenheit rise of temperature. This makes the change in volume directly proportional to the absolute temperature and means that approximately each 5° F. increase in temperatures makes an increase of 1 per cent in volume and each 5° F. decrease in temperature makes a decrease of 1 per cent in volume. For specific application of this see page 471. GAS SAND OR GAS ROCK. In no case is the gas found in rooms, caverns, or large crevices, as popularly supposed. "The oil and gas sands are simply very porous rocks which contain not only one great cavity, but millions upon millions of small or microscopic cavities, so that the oil, gas, water, or all three together, it may be, occupy these numerous little spaces, and thus saturate the rock just as water does a piece of cloth or a sponge when dipped into the same. The larger these pores are, and the greater the volume they occupy in proportion to the volume of the rock mass, the greater will be the contained oil or gas supply, and this proportion in fairly good producing sands, usually varies between one-fifth and one-tenth." 2 DEFINITION OF ROCK PRESSURE. When nature generated or deposited the natural gas in the rock reservoir-made up of the microscopic cavities between the sand grains a fixed amount of gas was placed in a fixed inclosed space. The pressure in the rock-called "rock pressure "was the result of the pressing into this fixed rock space of a larger volume of gas than the mere free air capacity of this rock reservoir. The degree of compression employed by nature in the formation process deter1 Deviation of Natural Gas from Boyle's Law, by Robert F. Earhart and Samuel S. Wyer. Transactions American Society Mechanical Engineers, vol. 38, p. 285. 2 I. C. White, West Virginia Geological Survey, vol. 1, p. 155. mined the intensity of the resulting pressure in the reservoir; that is, a high degree of compression produced a high rock pressure, and a low degree of compression produced a low rock pressure. Typical rock pressure decline curves are shown in figures 3 and 4. WELLS USED TO A VERY 6061 0161 WAYNE CO WEST VA Kermit 1161 MINGO Co. 1912 1913 LOCATION OF KERMIT 175 150 FIG. 3.-DECLINE IN ROCK PRESSURE OF NATURAL GAS WELLS OF THE WHY ROCK PRESSURE AND VOLUME MUST DECLINE. The rock pressure and volume must decline as gas is removed, because in the removal of the deposit of gas we are confronted with the following: 1.-A fixed volume of the reservoir. 2.-A fixed amount of gas inclosed in this fixed reservoir. 3.-A certain rock pressure resulting from the contraction of the gas volume into the fixed reservoir. Now, if a part of this fixed volume of gas is removed by tapping the reservoir from the surface of the earth, the remaining gas volume 90682-18-Bull. 102- -2 ROCK PRESSURE IN LBS. PER SQ. IN. expands and keeps the reservoir completely filled, but at a lower pressure. Rock pressure decline is therefore inevitable whenever any gas is removed. REGENERATION. Food and trees can be grown. Water supplies are constantly replenished by nature, but there is no regeneration in natural gas; and FIG. 4.--DECLINE IN ROCK PRESSURE OF NATURAL GAS WELLS OF THE UNITED when the gas is once used it is gone forever. While no one knows exactly how the natural gas is formed, yet enough facts are known about it to indicate that nature's process was a very slow one. It has taken millions of years to make the present concentrated supplies, and even though gas should now be formed in some parts of the earth's crust, the rate of formation will be so slow as to make such new gas pools of no interest or economic value for centuries, if ever. STORAGE OF NATURAL GAS. Storage facilities for natural gas are not commercially feasible in the field nor at the delivering end of the transmission line, except the very limited use of existing gas holders in distributing plants. The large variation in service demands must therefore be met by the wells and reserve acreage. That is, the entire field operations must be subordinated to the peculiar service demands måde on the natural gas company. An interesting contrast with these stringent operating conditions is the large storage equipment in acres of tank farms that may be used to equalize the load in the oil industry. LIMITS OF GEOLOGY, While earth structure is the essential element in the accumulation of large quantities of natural gas or oil, geological science is a directional indicator and hazard reducer only, and not a guarantor of commercial results. Geology answers that by careful attention to her precepts, much of the waste that characterized the first three decades of the search for petroleum can be avoided, but that it is beyond her powers to foretell absolutely as to whether any particular boring will yield either oil or gas in commercial quantity. The careful geologist can eliminate many of the factors of uncertainty, and thus limit the search to regions having a peculiar geological structure where experience has shown that the occurrence of oil and gas is most probable, but further than this geology can not go, and no skillful geologist has ever claimed otherwise.1 LIMITS OF UNDERGROUND RESERVOIRS. There is absolutely nothing fixed from the surface, and while surface conditions may be indicative, the question of underground location can be established by the drill alone. Even the presence of gas sand is not necessarily an indication of the presence of gas, as many dry holes show the full sand formation, without any gas in the sand. The dry holes shown in the map of the Triple State Field on plate 7 indicate a typical field situation, emphasizing the inability to determine underground limits except by drilling a hole. OPEN OR NATURAL FLOW. The courts have used the term "natural flow" synonomously for the engineering term "open flow," both, however, meaning exactly the same thing. The term."natural flow" necessarily means the entire volume of gas that will issue from the mouth of a gas well when retarded only by the atmospheric pressure. (Appellate Court of Indiana, 66 N. E., p. 782. Richmond Natural Gas Co. versus Enterprise Natural Gas Co.). 1 I. C. White, West Virginia Geological Survey, vol. 1, p. 158. The marked difference between the open flow of a gas well and the actual flow that may be obtained under routine operating conditions is emphasized in the next section. MISLEADING WELL CAPACITY. The natural gas well capacities that are given to the public are always the open flow capacity; that is, the capacity of the well in 24 hours when discharging freely into the atmosphere with no back pressure at all. This is misleading, and comes far from representing the true service capacity or true gas delivery capacity under routine operating conditions, of any gas well, because: 1. The first open flow measurements, which are usually the ones advertised in the newspapers, are nearly always made by the drillers, who do not have the facilities or skill to make an accurate test, and the errors are invariably on the side of a capacity larger than the actual facts. The volume is determined immediately after the well comes in, and is therefore larger than it would be several days afterward, on account of the fact that the well has not been drawn upon. 2. In routine operations of natural gas wells it is not possible to keep a well in service 24 hours, day in and day out. For various operating reasons, such as repairs, salt-water troubles, etc., it is necessary to rest wells at intervals. For this reason, the actual operating period of a well will be, on an average, very much less than 24 hours a day. 3. It is not feasible to maintain atmospheric pressure conditions in the pipes into which the wells discharge, but, on the contrary, the pressures are very much higher than atmospheric pressure. For this reason, the wells must discharge against considerable back pressure, thus retarding the amount of gas that will go out. 4. Based on actual operating tests, it has been determined that 25 per cent of the open flow capacity is about all that can be delivered from the average natural gas well. It must also be borne in mind. that the open flow capacity will constantly decrease, with the removal of gas from the well. 5. As the rock pressure declines it will be necessary to install compressing stations in order to transmit the gas into and through the main transmission line. 6. After the compression station has been installed, the further inevitable decline in rock pressure will lower the capacity of such station, as shown on page 29. MIGRATORY AND FUGITIVE NATURE OF NATURAL GAS. Natural gas has no fixed position under any particular portion of the earth's surface. On account of its inherent tendency to expand it has the power, as it were, of self transmission and is capable of flow |