Caldwell County Research Articles

Exploration History of South Texas Lower Cretaceous Carbonate Platform

The search for hydrocarbons in reservoirs of the Lower Cretaceous of south-central Texas has been continuous for more than 60 years. Accumulations have been found in significant quantities in only four areas: (1) the very shallow fault traps high on the San Marcos arch in Caldwell and Guadalupe Counties, (2) a fault trend stretching across central Atascosa County, (3) a fault trend extending from southeastern Atascosa County to southern Gonzales County, and (4) a narrow, elongate band extending across the entire area known as the Stuart City reef trend. Additional minor discoveries are widely scattered in the Maverick basin and San Marcos arch. Reservoirs which contain the hydrocarbons were deposited in many environments, all related to a broad carbonate shelf covered by an extremely shallow sea. The sea deepened dramatically at the shelf margin parallel with a reef trend. Dolomites contain the best accumulations in the fault trends, and porosity and permeability are reasonably good. Generally, limestones in the reef trend were not extremely porous initially, and late cementation has diminished even that porosity making the reservoir of lesser quality. Oil is the dominant hydrocarbon in the shallow fields, is less dominant in the other fault trends, and is nonexistent in the reef reservoirs. Proved ultimate hydrocarbons for the platform are about 363 million bbl of oil and 1.7 Tcf of gas. Reserves for the reef trend's dry gas reservoirs are difficult to estimate because of highly variable reservoir conditions, but they should fall between 1 and 1.5 Tcf. Exploration has been most intense for the uppermost Lower Cretaceous rocks. The Sligo limestone still holds the promise of success, but lies at considerable depths over much of the area. Edwards and Glen Rose rocks are more densely explored, but there are ample opportunities for new plays even in these formations. Geologists who examine cores and cuttings, determine depositional patterns, understand modern carbonate sedimentology, and study patterns of diagenesis will have an advantage in developing new concepts for exploration.

Application of SP Curves to Corrosion Detection

Application of SP Curves to Corrosion Detection

Pisolites Formed from the Oilfield Water of the Luling Field, Caldwell County, Texas

ABSTRACT Pisolites were being formed in 1936 during aeration of the water from the oil wells of the Luling Field, Caldwell County, Texas. The field is a faulted monocline. Production is from the Edwards (Comanchean Cretaceous). In the wells, the Edwards is porous and rotten with oil in its upper portion and water in its lower. The oil and water were produced together and separated in settling tanks. The water was hot, saline, carbonated, and saturated with hydrogen sulphide. This poisonous gas had to be removed before the water was discharged into stream floodwaters. It was removed by aeration. The well water was led through pipes several inches in diameter to the top of wooden towers some 12 ft high where it was discharged. Pisolites formed in the violently agitated pools on the floor below. The pisolites ranged from 3 mm to 50 mm in diameter, and their shapes ranged from spherical to ovoid to irregular. Their centers were irregular and usually surrounded by many thin concentric crystalline layers of calcium carbonate, probably aragonite. A few years after 1936 the method of aeration was changed.

Organizing Mass Gamma Globulin Clinics in Three North Carolina Counties

SOME 30,000 children were inoculated with gamma globulin on a mass basis in three western North Carolina counties during the period from July 6 to August 7, 1953. Inoculations were given in Caldwell County on July 6, 7, and 8, and 12,800 children were processed in the 3 days. Catawba County was the site of a 3-day inoculation program on July 15, 16, and 17, at which time 14,761 children were given gamma globulin. In Avery County, during a 2-day program on August 6-7, 3,092 children were inoculated. The pattern developed for operating the mass gamma globulin clinics in North Carolina has proved to be highly effective. This discussion outlines the purely administrative aspects of formulating and operating a globulin mass inoculation clinic. The criteria which must be fulfilled by a county prior to receiving globulin from the Office of Defense Mobilization varied according to the amount of globulin available, and these, accordingly, are not included.

Petrography and Metamorphism of Sediments of Ouachita Facies

Sediments of Ouachita facies extend in the subsurface from the Ouachita Mountains of Oklahoma and Arkansas to the Marathon and Solitario uplifts of extreme southwest Texas. Although these sediments have been subjected to strong dynamic metamorphism, the metamorphic grade attained is uniformly low. Sediments of Ouachita facies are essentially unaltered in some areas; elsewhere they range in degree of metamorphism as high as the biotite zone. Mineralogical change and cataclastic effects are key criteria for discerning the stages of progressive metamorphism in sediments of Ouachita facies. Metamorphic changes are most easily observed in shales and argillaceous sandstones; limestones and cherts react less conspicuously to metamorphic stress. The so-called schist of the Luling field, Caldwell County, Texas, and of some other deep wells along the Luling-Mexia-Talco fault system consists for the most part of metaquartzite, meta-argillite, phyllite, and slate. With two possible exceptions, these metasediments are restricted to the chlorite and biotite zones and are comparable in mineralogy and degree of metamorphism with sediments exposed in the more highly metamorphosed parts of the Ouachita Mountains of Oklahoma and Arkansas.

Petrography and Metamorphism of Sediments of Ouachita Facies: ABSTRACT

Sediments of Ouachita facies extend subsurface from the Ouachita Mountains of Oklahoma and Arkansas to the Marathon and Solitario uplifts of extreme southwest Texas. Although these sediments have been subjected to strong dynamic metamorphism, the metamorphic grade attained is uniformly low. Sediments of Ouachita facies are essentially unaltered in some areas; elsewhere they range in degree of metamorphism as high as the biotite zone. Mineralogical change and cataclastic effects are key criteria for discerning the stages of progressive metamorphism in sediments of Ouachita facies. Metamorphic changes are most easily observed in shales and argillaceous sandstones--limestones and cherts react less conspicuously to metamorphic stress. Mineralogical change resulting from metamorphism reduces the porosity and non-fracture permeability of sandstones to such an extent that they are not good petroleum reservoirs. The petrography of the so-called schists of Luling field, Caldwell County, Texas, and of some other deep wells along the Luling-Mexia-Talco fault system is discussed briefly. It is shown that they are generally comparable in mineralogy and degree of metamorphism with sediments exposed in the Ouachita Mountains of McCurtain County, Oklahoma. End_of_Article - Last_Page 2626------------

Balcones, Luling, and Mexia Fault Zones in Texas

The Balcones fault zone crosses the San Marcos arch and is located between the comparatively flat dip of the Edwards Plateau and the more steeply dipping beds of the Coastal Plain. It is composed principally of faults with downthrown side on the southeast. The throw on faults of this zone approximates 1,200 feet in northwestern Bexar County. The Luling fault zone lies coastward from the Balcones fault zone and is composed principally of faults with downthrown side on the northwest. In Caldwell County along San Marcos River a total throw of more than 1,500 feet is indicated by faults of the Luling type. The Mexia fault zone lies eastward and southeastward from the Luling zone and is characterized by faults with downthrown side on the southeast and by faults with downthrown side on the northwest. Both commonly occur with a graben of varying width between them. This zone of faults extends from north and northeast of Mexia, Limestone County, southwest through parts of Milam Burleson, Lee, Bastrop, Fayette, Gonzales, and probably through parts of De Witt, Karnes, Goliad, Bee, Live Oak, and Duval counties. Major movement along these faults probably occurred in late Catahoula or early Oakville (Miocene) time, thus affecting sedimentation of this period. Minor faults are present in Pliocene and basal Pleistocene formations. Some Recent movement is recorded.

Gideon Oil Well No. 3, Luling Field, Caldwell County, Texas: GEOLOGICAL NOTES

Gideon Oil Well No. 3, Luling Field, Caldwell County, Texas: GEOLOGICAL NOTES

Salt Flat Oil Field, Caldwell County, Texas

The Salt Flat oil field in southern Caldwell County, Texas, was opened October 13, 1928, making the third oil field in Caldwell County producing from the Edwards limestone. A daily peak of 52,013 barrels was reached on June 18, 1929. In all, 343 wells have been drilled, only 25 of which are dry holes. The Salt Flat field is located parallel with, and on the southeast or upthrown side of, a fault which strikes N. 30° E. The fault has a maximum vertical displacement of 375 feet. The pay formation is the upper 25-35 feet of the Edwards limestone (Comanche), which is a porous dolomitic limestone with lenses of indurated cherty limestone. The upper few feet of the pay formation is ordinarily soft yellowish limestone, commonly referred to as dobe. A few wells have encountered commercial production above the Edwards limestone. The surface beds in the Salt Flat field are Wilcox sand and shale, which are Eocene or early Tertiary in age. The Salt Flat field, which consists of 1,196 productive acres, produced 13,790,362 barrels of 36° gravity oil (A. P. I.) to the end of 1929. It is estimated that the ultimate recovery will be approximately 30,000 barrels per acre, or a total recovery of approximately 36,000,000 barrels of oil for the entire field. The average depth to the pay horizon is 2,700 feet, and rotary methods of drilling have been used exclusively. Most of the wells are pumped with individual electric pumping units.

Geology of Larremore Area, Caldwell County, Texas

The writer describes the geology of the structure upon which the Larremore oil field is located. This field is also known as the Jolly or Roxana field, as the discovery well was drilled on the A. W. Jolly farm, C. Crenshaw Survey, by the Roxana (now Shell) Petroleum Corporation. The oil is obtained from the Edwards limestone encountered at a depth of approximately 1,285 feet. This is the second Edwards limestone field discovered in the United States.

Electrical Survey of Structural Conditions in Salt Flat Field, Caldwell County, Texas

The writer points out the difficulties in mapping the oil structure of the Balcones fault zone in Texas in the usual way, by a study of surface geology. Core drilling has been used in many places, but has not proved very successful on account of the uncertainty involved in identifying the beds and in correlating them between holes. He discusses the application, in this area, of the Sundberg electromagnetic method of mapping structure, describing the basic principles and showing it to be much superior to core drilling in speed and efficiency. The survey made by the Sundberg method in the Salt Flat, or Bruner, oil field was begun in October, 1928, when only the discovery well was productive, and before the trend of the producing fault structure was known. The fault was mapped electrically by one surveying crew in about a month, and the later development of the field has proved the results correct, as shown by the map. A comparison of these electrical results with the data obtained from later drilling gave excellent agreement, as shown by five different profiles across the field.

Some Issues in Chester Stratigraphy in Kentucky and Illinois

This paper is a contribution toward the settlement of a long-standing controversy concerning certain points in Chester stratigraphy in Kentucky and Illinois. The late Professor Weller correlated the Renault formation of Randolph County, Illinois, with both the upper part of the Ohara limestone and the lower part of the Gasper limestone, and also correlated the Bethel sandstone of western Kentucky with the Sample sandstone of Breckinridge County, Kentucky. He and his son, Dr. Marvin Weller, denied the validity of the name Gasper and used, instead, the hyphenated designation Renault-Paint-Creek. Professor Weller also questioned the suitability of the name Bethel for the sandstone unit so named. The present paper presents concrete evidence tending to disprove the views of the Wellers on the points mentioned. Certain characteristic species of fossils mark the lower part of the Gasper beneath the Sample sandstone and the same assemblage occurs in Christian and Caldwell counties, Kentucky, in the lower part of the typical "Tribune" limestone of Ulrich (for which the name Gasper was substituted), and above the Bethel sandstone and hence above the Ohara limestone which immediately underlies the Bethel sandstone in western Kentucky. Not one of the characteristic members of this fauna has ever been found in the Ohara limestone or below the horizon of the Bethel sandstone. From this it follows that the Bethel and Sample sandstones are not the same. Therefore the Renault formation cannot be the equivalent of both the Ohara, which is below the Bethel, and the "lower Gasper," which is above the Bethel. As it is admitted by the Wellers that the Gasper is an indivisible unit equivalent to the Renault and Paint Creek, and as the name is applied in accordance with the customary modern practice of giving a new name to two or more combined units, its validity cannot be fairly questioned. In regard to the name Bethel, it is shown that the sandstone near Bethel school, now Crittenden Springs school, which Weller thought to be the lower part of the Cypress sandstone, is directly underlain by the Ohara limestone and therefore clearly Bethel, so that the name is entirely appropriate.

The Lytton Springs Oil Field, Caldwell County, Texas

The Lytton Springs oil field is located in the northern part of Caldwell County, Texas. It covers an area approximately 1½ miles in diameter. The discovery well was brought in on March 13, 1925, at a depth of 1,350 feet and the following March there were approximately 325 producing wells in the field. Midway and Wilcox formations are exposed at the surface. The producing formation is an altered igneous rock, referred to as serpentine. This rock probably represents an old, buried, volcanic cone with a relief on its upper surface of over 600 feet. Production is obtained throughout this vertical range, the oil generally being found within 200 feet of the top of the serpentine. The exceptional feature of the field is the general lack of water in the producing formation, even in the edge wells 600 feet below the crest of the dome. The peak of production for this field, about 15,000 barrels per day, occurred four and one-half months after the completion of the discovery well. By the end of March, 1926, the production had settled to about 8,000 barrels per day. The oil is of high grade, having a gravity of about 38° Baume and a value of about two dollars per barrel at the well (March, 1926).

The Luling Field, Caldwell and Guadalupe Counties, Texas

The Luling field, in Caldwell and Guadalupe counties, Texas, is a fault structure located about 20 miles southeast of the main Balcones fault. The area is drained by San Marcos River. The Wilcox formation is exposed at the surface and the producing formation is the Edwards limestone of the Comanchean Cretaceous. The field is 7.5 miles long and averages about ½ mile wide. The discovery well was brought in on August 14, 1922. On December 31, 1924, there were 391 producing wells in the field. The structure is a faulted monocline limited on the northwest, northeast, and southwest by faults of about 450-foot displacement. The strike of the structure is NE.-SW. The heave of the fault measured on the top of the Edwards is 1,000-1,800 feet. The highest points of the structure are near the two extremities of the field, the middle portion being about 40 feet lower. The sedimentary column seems to overlie a metamorphic basement composed of rocks of early Cretaceous or pre-Cretaceous age. The average depth of the top of the Edwards oil horizon is about 2,100 feet. The oil is of about 27° Baume gravity. The total production of the field to December 31, 1924, was about 14,500,000 barrels and the daily production about 30,000 barrels.

The Luling Oil Field in Caldwell County, Texas

The Luling Oil Field in Caldwell County, Texas

Oil at Luling, Caldwell County, Texas: GEOLOGICAL NOTES

Oil at Luling, Caldwell County, Texas: GEOLOGICAL NOTES