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The question of natural-gas supply is receiving careful consideration inmany parts of the country, as in the winter months it is quite a problem tohave on hand sufficient gas to satisfy the demand. Increasing the output ofwells by the application of vacuum has been tried with various results andlarge companies have attempted to keep up the supply with gas compressors. Thepossibility of storing natural gas in the sands of exhausted gas pools has beentried in a few instances with satisfactory results. This method may prove ofpractical value in solving the problem, especially in the case of towns thatformerly obtained gas from their immediate vicinity but now must search for newpools.
In all cases, only part of the available supply is utilized during the warmweather, so that many wells are shut-in, yet during the winter months, thesupply is not sufficient even with all the wells on the line; in such cases itwould be of great value if a large volume of stored gas were on hand, obtainedthrough wells that would have been standing idle during the summer.
Idle producing wells having considerable ?rock pressure? will force gas intothe exhausted, or storage wells, and this gas will be used only when theregular supply falls short (Fig. 1). If two gas wells of different pressuresare connected, the one having the greater pressure will feed the other, untilthe pressures are at an equilibrium. The same results will be obtained if anexhausted gas well is connected to a high-pressure gas line. High-pressurelines equipped with regulators near the town plant have considerable pressure,so that storage wells connected to such a line will receive gas from the lineas long as the line pressure is greater than the well pressure. During a periodof heavy consumption of gas, the pressure on the main line is greatly reduced,so that gas from the storage wells will flow into the lines. An arrangement ofthis kind will work automatically, the flow of gas into or from the storagewells depending on the pressure carried in the line.
It is advisable in most instances that the flow into and from the storage wellsbe regulated by means of gates, instead of automatically. In addition, thevolume of gas should be metered as it is forced into or passes from the wells;the pressure also should be noted. By properly charting the meter and pressurerecords, the characteristics of the individual wells may be determined.
The following example of the practical application of engineering geology isof interest in that it demonstrates the advantage of keeping accurate recordsof all wells, whether drilled by one's self or by others, together with theadvantage gained by gathering such data during the process of development. Thefault described was found in the autumn of 1915, during the hurried developmentcaused by the discovery of the famous Gusher Bend pool in Red River Parish,Louisiana. The writer was at the time employed by one of the operatingcompanies as geologist, and the example is a portion of the routine work.
The oil fields of northern Louisiana and east Texas are located in Caddo,Bossier, De Soto and Red River Parishes, Louisiana, and Marion County, Texas. Avery narrow strip of the eastern portion of the latter is productive. Theproducing oil pools are known as the Caddo Field, in the northern part, and theDe Soto-Red River Field, in the southern. The two fields are 60 miles apart.There are several gas fields between them, but no important supply of oil hasbeen found, though there are several producing wells in the Anona chalk,locally called the Chalk Rock, in the Elm Grove gas field in Township 16 North,Range 11 West (see Plate 1).
General Geologic and Structural Features
The general geology of northern Louisiana has been excellently described byA.C. Veatch in Professional Paper No. 46, U.S. Geological Survey; by G.D.Harris, Bulletin No. 429, U.S. Geological Survey; and later by George C. Matsonand Oliver B. Hopkins in Bulletins No. 619 and 661C, U.S. GeologicalSurvey.
This paper summarizes the results obtained from the preliminary cementing of wells in an effort to cut off the bottom water. The object of this work was two-fold:
(1) To prevent the oil sand from becoming flooded.
(2) To plug off bottom water, thereby preserving the individual well and reclaiming production.
Valuable suggestions and help have been given by the following named: Messrs. Kyle and La Velle, of the U. S. Bureau of Mines; Magnolia Petroleum Co.; Freed Oil and Gas Co. The cementing work was carried out under the personal supervision of L. J. Snyder.
In an unpublished paper on the “Water Problem in the Augusta Field,” S. K. Clark reaches the following conclusions:
(1) That the great amount of water present is bottom water, occurring in the Varner sand, the main producing or the 2500-ft. horizon.
(2) That the only striking connection between structure and water is in the area of the marked fault on the Ralston, E. C. Varner, and F. Varner leases in sections 8, 9, 16 and 17.
(3) That the oil occurs in porous streaks, generally separated by fine-grained, well cemented sand, which is barren. Possibly two or three such pay streaks may be found. That under a pay, fine-grained sand occurs, which is presumably barren at the time of drilling, but soon reveals water.
The writer takes partial exception to the last point, because well defined shale, slate, lime, or hard sand breaks have been encountered in a great many cases, separating the pay streaks under which water is often found. This is not an invariable occurrence, as cases have been noted when the oil has been followed immediately by water in the same stratum.
In an effort to overcome the water menace, the following methods of plugging were tried:
(1) Plugging with wood, lead, and limit plugs.
(2) Plugging with sand pumpings.
The rapid increase of water troubles in the Mid-Continent oil fields iscausing much alarm. Troubles occur at Towanda, Eldorado, Augusta, Cushing,Blackwell, and Healdton, although they had not been acute in the Mid-Continentfield until about two years ago, when the unusual conditions in the deeper oilfields were first encountered. California faced the same situation, but, thanksto aggressive measures, has largely overcome the dangers.
The following analysis of water trouble may throw some light on the subject andbe of assistance in solving the problems involved.
Water Troubles Classified
The presence of water in large quantities in oil sands has the followingresults:
1. Diminishes oil production.
2. Diminishes casing-head gasoline production:
(a) By curtailing the gas flow.
(b) By making the use of vacuum pumps unsuccessful.
3. Increases lifting costs:
(a) By making it necessary to pump large quantities of water, which requires afast motion and long stroke (third hole).
(b) By requiring the use of compressors for air lift.
(c) By causing break-downs and delays due to the high speed necessary to pumpwater.
(d) By making it necessary to treat ?cut? or emulsified oil.
Oil production is seriously curtailed by the presence of large quantities ofwater. Lease records show that wells are shut down 40 to 60 per cent of thepumping time where serious water trouble occurs. While a small quantity of saltwater may cut the paraffin and keep the oil moving, several hundred feet, or ahole full of water, effectually ?kills? the oil and gas. The quick return ofwells to production, once the water is shut off, shows how wells have beenaffected.
THE great activity with which the oil resources of the northern Cantons of the State of Veracruz have been developed has largely resulted from the great success obtained by the important explorations carried out since 1902 in the Ebano district in the North, and several years later near Tuxpam, in the South. The discovery of oil in industrial quantities at Cerro de la Pez, Ebano district, and the famous Dos Bocas gusher some years later, which was burned, once and for all made famous the Veracruz coast, where today is conccntrated the Mexican output of mineral oil. In 1917, this production was nearly 61,000,000 bb1. It is well Imwn that this output represents only a fraction of what the wells in actual production can furnish, because with adequate means of transportation and storage, the present extraction could be somewhat over 300,000,000 bbl. a year. These enormous potential oil resources of the Veracruz coast proceed from a relatively small number of wells, scattered over a few oil fields, separated from each other by large unexplored areas, wherein may be found other favorable fields which, in time, will undoubtedly become just as great centers of oil production.
There are two main sources of the water that floods productive oil or gassands. The water may rise from the lower depths of the producing stratum, or itmay come from beds above or below the oil-bearing formation. Usually therecovery of oil is decreased by water entering the oil sands, and mostoil-field waters, especially those of deep wells, tend to foster the formationof an emulsion, which is expensive to treat. This paper deals with a method ofdistinguishing between waters that encroach upon oil-bearing beds from sourcesin the same stratum and waters that reach the oil sands from horizonsabove.
In order to remedy effectually water difficulties in oil and gas wells, it isabsolutely necessary to determine the source of the invading water. Sometimesevidence such as the structural relations between the strata penetrated byneighboring wells and those found in the well under investigation is notadequate; also, data from drill logs and well records, from mechanical testsmade on the wells by plugs, testers, drilling tools, etc., and from tests bychemical indicators such as eosin and Venetian red, may be unsatisfactory, forsuch data may fail to locate the source of the infiltrating waters. As a resortin such cases, the application of chemical analyses, that is, the comparison ofan analysis of the water in question with that of typical waters from thevarious water horizons in that particular district has in certain instancesproved of value. This method has been used to advantage in the WestsideCoalinga field of California, where the source of water may be fairlydefinitely determined, from its composition.
The chief conclusions concerning the chemistry of the oil-field waters inCalifornia by G. S. Rogers are: Oil-field water is not necessarily salty, as isgenerally believed, and may not be even slightly salty to the taste. The degreeof concentration of chloride in such water is governed primarily by localconditions and is not affected by the position of the water in relation to oil.Sulfate diminishes in amount as the oil zone is approached and finallydisappears.
Considerable interest has been shown, during recent years, in thepossibilities of developing oil fields in the South American Republics, nowthat the exhaustion of our present fields can be seen in the not very distantfuture. The demand for fuel oil and its products has been increasing far morerapidly than our increment of production during the last few years. Increase ofconsumption has been largely curtailed by the lack of sufficient supply. Themain factors that have contributed to our previous neglect of the southernfields have been as follows:
(a) Lack of sufficient demand for the product.
(b) Competition with producing fields, having large production, low cost, andbetter geographical position, such as Tampico, Mexico.
(c) Greater interest in home fields with ready market at hand.
(d) Our ignorance of southern economic and geologic conditions, due to thedistance between those areas and our financial centers.
(e) Economic conditions in the southern countries, necessitating high costs ofexploration and exploitation of the fields.
(f) Our lack of understanding of the business methods of the LatinAmerican.
It must be borne in mind that the oil-development work done to the present timein South America has, with one exception, been undertaken upon lands whichpossessed direct evidence of oil in seepages or asphaltic deposits, occurringeither immediately upon the lands or in their close vicinity. The developmentof oil fields in South America is therefore in the pioneer stage. It is not atall improbable that ?hidden fields? will be uncovered in future work, as hasoccurred notably in the mid-continental field of this country within recentyears.
North Central Texas has recently become a center of interest for the oil menof America. The bringing in of the McClosky well at Ranger, Eastland County,and the shallow pool at Brownwood, Brown County, in 1917, has stimulatedinterest in this area to fever pitch. Oil men from all over the United Statesare now investing there. The area of present interest is shown by theaccompanying map (Fig. 1).
The money spent in leases runs into millions of dollars. It is no exaggerationto say that a strip of country 200 miles (321 km.) long and 125 miles (201 km.)wide, comprising some 15,000,000 acres (6,070,310 ha.), has been leasedpractically solid at a cost for rentals and bonuses of at least $1 per acre.The test holes contracted for will certainly number 400, at a cost of at least$5,000,000. From what has been done in the past six months, $20,000,000 atleast will be spent. To pay returns on this amount of money, new production tothe extent of at least 12,000,000 bbl. must be obtained. At present, theproduction from new fields will not average over 5000 bbl. per day; three wellsat Ranger are producing 3000 bbl.; 250 wells at Brownwood produce 1000 bbl.;and the Gray well, Coleman County, is as yet an unknown factor.
However, at Ranger there is every indication of developing a good pool coveringfrom 1500 to 2000 acres (607 to 809 ha.), more or less, but the wells are deep,3400 to 3800 ft. (1036 to 1158 m.), and cost $35,000 to $40,000 to drill. Largewells are necessary to pay for such expensive holes. As new wells are drilled,the gas pressure will be lowered rapidly, and large production need not beexpected. For those oil men who expect a second Cushing or an Eldorado, Rangerholds little of promise.
At Brownwood, Brown County, there are some 250 shallow wells (depths from 200to 350 ft.) averaging 4 to 7 bbl. per day. There is a chance of an extensiveproducing area for these shallow sands to the southwest, and the opening ofseveral thousand acres of shallow oil territory, and also some promise ofdeeper oil horizons in the Ranger horizon, but probably all under 2500ft.
At present, the lease brokers and speculators, and only a handful of oil men,have made any money. More fields must be developed, and it is more particularlywith these possibilities that this paper deals. Lack of water for drillingpurposes has undoubtedly held back development so far this year; this part ofTexas has had a drought for two years and there is an actual scarcity ofwater.
New fields are being discovered from time to time and doubtless some still remain to be found, though of ' late years discoveries have become more infrequent. Careful geologic work within the fields has in some cases increased the production temporarily, but has developed no really new supplies. The Gulf Coast oil industry seems to have passed its period of greatest expansion and to be declining at a fairly steady rate, and this condition is naturally viewed with alarm by the more farsighted operators. In my opinion, the time has come for the adoption of radical and aggressive methods of prospecting; and a fraction of the money wasted yearly in drilling shallow wells in hopeless locations might well be devoted to this purpose. Many facts lead me to believe that all the salt-dome oil has had a common origin; that it has migrated up from considerable depth along lines of structural weakness; and that a deep well, properly located, stands an excellent chance of discovering the parent reservoir and thus of developing new and probably great supplies. This paperis presented as a discussion-necessarily hypothetical and based largely on personal opinion-of the possibility of encountering deep-seated oil deposits beneath the salt domes. AU of the oil produced in the coastal region of Texas and Louisiana is probably associated with salt domes, though in Goose Creek, Edgerly, and one or two'other fields no salt has yet been actually penetrated. As 502 DEEP-SEATED OIL DEPOSITS ON GULF COAST a result of the innumerable wells that have been drilled on the various domes, it is now known that a typical salt dome consists of a very thick mass of pretty pure rock salt, generally almost flat-topped, but sloping abruptly away from the rim on every side.
Since the opening of the Wheeler oil and gas field in Carter County and thediscovery of oil near Lawton, Comanche County, Okla., in 1904, interest hasbeen aroused regarding the origin of the oil in the Permian ?Red Bed? regionwhich lies between the Wichita and Arbuckle Mountains on the north and the RedRiver on the south. The later development of the Healdton, Loco, Duncan, Fox,and Graham fields south and west of the Arbuckle Mountains has brought theregion into prominence, Recent discoveries of Ordovician and of Pennsylvanianfossils in wells in the Healdton field and of Pennsylvanian fossils in the Foxand Graham fields are of such importance from a scientific and a commercialstandpoint that the occurrences and the problems arising therefrom are herebriefly described.
Producing oil and gas sands in the southern Oklahoma fields, with the exceptionof those in the Cretaceous and underlying rocks in the vicinity of Madill,Marshall County, are associated with the Permian ?Red Beds? or with theunderlying Paleozoic strata. In the two fields farthest south of the ArbuckleMountains, Healdton and Loco, production has been entirely confined to sands atdepths of 700 to 1400 ft. (213 to 416 m.) and only recently has a producingsand as deep as 1860 ft. (567 m.) been encountered. These sands are found nearand below the base of the red rocks and were supposed by Wegemann and Heald tobelong in large part to the basal Permian, Wichita formation, or to theimmediately underlying formations. Fossils in the blue shales and in thelimestones associated with the deeper sands now prove them to be Pennsylvanianand all the producing sands at Healdton are found to be of this age.