Lower Glen Rose Research Articles

Carbon isotope chemostratigraphy of the Yucca Formation from the Solitario, Big Bend Ranch State Park, Texas

Introduction: The Yucca Formation is a Lower Cretaceous sedimentary unit present in West Texas. Based on its relative stratigraphic position in the Cretaceous succession of West Texas, it is expected that the Yucca Formation is of Albian and/or Aptian age. It is also expected that the carbon isotope excursions associated with OAE 1a and OAE 1b should be identified in the Yucca Formation. The goals of this project are to 1. construct a carbon isotope chemostratigraphic record of the Yucca Formation, and 2. correlate the Yucca Formation with strata of similar age using chemostratigraphy.Methods: 163 samples were collected from Big Bend Ranch State Park (BBRSP) to determine the δ13C value of bulk sedimentary organic matter.Results: C-isotope values range from −27.02‰ to −18.42‰.Discussion: Carbon isotope excursions (CIEs) that are associated with the Aptian-Albian Boundary are identified as well as CIEs associated with Oceanic Anoxic Events (1a and 1b). This allows us to conclude that the Aptian-Albian boundary is recorded within the Yucca Formation strata at about 71 m above the base of the section exposed in the Lower Shutup of the Solitario in Big Bend Ranch State Park. Regional correlation of the Yucca Formation to other chemostratigraphic records from other Cretaceous strata suggests that the Yucca Formation in BBRSP is time equivalent to the Sligo, Pine Island, James, Bexar, and a portion of the lower Glen Rose Formation on the Comanche Platform and to a portion of the lower Glen Rose Formation in Big Bend National Park.

Effects of Thalassinoides ichnofabrics on the petrophysical properties of the Lower Cretaceous Lower Glen Rose Limestone, Middle Trinity Aquifer, Northern Bexar County, Texas

The combined Edwards and Trinity aquifer system is the primary source of freshwater for the rapidly growing San Antonio and Austin metropolitan areas. The karstic Lower Cretaceous (Aptian–Albian) Lower Glen Rose Limestone (GRL) contains the middle Trinity aquifer and has been subdivided into six hydrostratigraphic units (HSUs) with distinct hydrologic characteristics. These HSUs were first identified in the subsurface via core examination at the Camp Stanley Storage Activity (CSSA) in northern Bexar County, Texas and were then correlated to associated gamma-ray and resistivity logs. The Trinity aquifer system is a telogenetic karst and fluid flow is directed primarily through solution-enhanced faults, fractures, and pervasive Thalassinoides networks because matrix porosity of both transmissive and confining HSUs is very low. Meteoric water infiltrates the Trinity aquifer through vertically-oriented faults and likely moves laterally through biogenic pores. Two 7.62cm diameter GRL cores and well logs from monitoring wells CS-MW9-CC and CS-MW5-LGR recovered from the CSSA were used to characterize the effect such large-scale Thalassinoides networks have on the petrophysical properties (resistivity and natural gamma-ray) of four HSUs (Honey Creek, Rust, Doeppenschmidt, and Twin Sisters HSUs). Resistivity logs show that resistance values >300Ω-m correlate with well-developed biogenic porosity and values of 650Ω-m are associated with solution enhancement of the Thalassinoides networks. These high resistivity zones are cyclical and are identified in muddy confining units, even when no changes in lithology or karstic development are identified. Pervasive Thalassinoides networks act as starting points for wide spread dissolution and lead to advanced karst development in transmissive HSUs. Natural gamma-ray logs do not reflect hydrologic characteristics directly, but are inversely correlated to resistivity logs and display m-scale cyclicity. Resistivity logs suggest that Thalassinoides networks are interconnected throughout strata within the GRL and when coupled with natural gamma-logs, the lateral distribution of these networks within HSUs can be correlated. Identifying such fluid pathways is of particular importance for wells not located in proximity to major faults and karstic features.

Pearsall (Aptian Cretaceous) Subsurface to Outcrop Sequence Stratigraphy, Central Texas: ABSTRACT

ABSTRACT Bexar (Upper Pearsall) Shale is a widespread subsurface body of marine clay mudstone; in south-central Texas it disappears updip along a line through central Medina and Bexar Counties and the northwestern edges of Guadalupe, Caldwell, and Bastrop Counties. Bexar Shale overlies calichified Cow Creek Limestone and underlies Hensel Dolomite; in outcrop Hensel Dolomite rests on calichified Cow Creek. The Cow Creek and other mid-Pearsall limestones are local high-stand deposits; the basal Bexar is a transgressive bed and the bulk of the unit a shoaling-upward ramp deposit. Hensel silty dolomite (laminated to churned, with glauconite, collophane, beekite, and milky quartz geodes) and overlying Lower Glen Rose grainstones (containing widespread subarkose sand grains) are a high-stand lagoon/bar sequence that overlaid Bexar Shale and spread 25 km inland from the Bexar pinchout. The Hensel/basal Glen Rose shoaling sequence is the earliest of three in the Lower Glen Rose. Type Hensel Sandstone around Lake Travis was deposited (from local flash floods) after 35 m of marine Bexar shale and 35-50 m of Glen Rose carbonates farther south (an ammonite zone later). Deep red clay between calichified Cow Creek and Hensel Sandstone around Lake Travis may be remnant Bexar Shale or may be local and unrelated. Actual eustatic/tectonic/sediment-supply history does not fit a simple sequence-stratigraphic pattern.

The paleoecological implications of the charophyte flora of the Trinity Division, Junction, Texas

The Trinity Division exposures at Junction, Kimble County, Texas, yield a rich charophyte flora dominated by clavatoraceans. The presence of Atopochara trivolvis ssp. trivolvis (Peck, 1938) Grambast, 1968, and Clypeator corrugatus (Peck, 1941) Grambast, 1962, indicates an Aptian age for these strata and makes them the continental equivalent of the Lower Glen Rose. Atopochara trivolvis, whose type-material was recovered from the Trinity in a deep well in southern Texas, is known from numerous freshwater to oligohaline lakes from the Mesogean area in Europe and North Africa as well as from Cretaceous oil-bearing basins in China. Charophytes are clear indicators of supratidal environments and the abundant remains at Junction suggest a positive structural feature in this part of central Texas that might have been either an island or directly connected to the Llano Uplift.

Burial Cements in Lower Cretaceous Pearsall Formation and Lower Glen Rose Formation, South Texas: ABSTRACT

Lower Cretaceous platform carbonates and shales were buried to depths in excess of 2,000 ft (610 m) by the end of Eocene time, and were locally affected by late-stage cementation. Burial diagenetic cements include ferroan baroque dolomite, ferroan and nonferroan calcite, anhydrite, kaolinite, barytocelestite, galena, and sphalerite. The lack of these minerals in outcrop and their occurrence in fractures are evidence for a subsurface origin. Carbonate cements are chemically and isotopically zoned; the FeCO3 content in baroque dolomite cement varies by as much as 10 wt. % across a single crystal. Stratigraphic and regional distribution of iron in baroque dolomite indicates that the iron is derived from local sources. Good negative correlation between ^dgr13C values and iron contents of baroque dolomite suggests the End_Page 572------------------------------ simultaneous reduction of iron oxides and oxidation of organic material. Some of the late subsurface carbonate cements with extremely depleted ^dgr18O values precipitated either from hot brine or from isotopically light water; both possibilities require the vertical movement of fluid along faults. Galena and sphalerite occur in small amounts in some cores; a single fluid inclusion homogenization temperature from sphalerite was 20°C (68°F) higher than the present formation temperature at that depth. Brines moving up faults after albitizing feldspars in more deeply buried formations could be the source of lead and zinc for these minerals. Strontium isotopic ratios for calcite cement in these rocks are similar to ratios for brines from the Stuart City reef trend that are believed to originate deep in the Gulf of Mexico basin. End_of_Article - Last_Page 573------------

Deposition of Prograding Carbonate Sand Shoals and Their Subsequent Diagenesis--Lower Glen Rose (Cretaceous), South Texas: ABSTRACT

End_Page 546------------------------------The lower Glen Rose in southwest Texas is a widely explored, but oil- and gas-barren, carbonate sequence (200 to 300 m thick) that was deposited on a broad, shallow-marine shelf. Three cyclic, shoal-water complexes, consisting of high-energy grainstone and coral-stromatoporoid-caprinid boundstone, developed over the Pearsall arch of south Texas. Facies distributions, determined from core and electrical logs, show that these linear complexes trend east-west for at least 125 km, and are located about 80 km inland of the Cretaceous shelf edge and 70 km seaward of the Cretaceous shoreline. The shoal-water, cyclic sequences change upward from: (1) sandy, fossiliferous mudstone/wackestone deposited in an open-shelf environment; (2) echinoid-mollusk and oncolite-caprinid packstone deposited in intertidal shoals and subtidal grain flats; (3) coated-grain and echinoid-mollusk grainstone deposited in sand flats, tidal channels, spits, and bars; and (4) coral-stromatoporoid-caprinid boundstone and packstone deposited as patch reefs and flanking deposits. Lagoonal deposits, consisting of toucasiid-oyster-miliolid wackestone, boundstone, and mudstone enclose each of the shoal-water sequences, and indicate successive seaward progradations, interrupted by transgressions of open-shelf facies. The patch reefs may have prograded out across the shelf and formed the initial buildup of he Stuart City shelf margin. Four gradational phases of grainstone diagenesis have caused almost continuous loss of porosity during burial. Micritic envelopes and isopachous crusts are early submarine cements. Next, development of an extensive meteoric-water system during burial to shallow depths led to dissolution or neomorphism of aragonite and precipitation of equant, isopachous cement, syntaxial cement, and nonferroan, equant calcite. As burial increased, subsurface brine displaced the original connate fluids and caused complex cementation and replacement by zoned ferroan and nonferroan calcite, lutecite and megaquartz, anhydrite, and saddle dolomite. The highest porosity is found in mappable facies of shoal-water grainstone. End_of_Article - Last_Page 547------------

Evolution and Porosity of Carbonate Shoaling Cycles, Lower Glen Rose (Lower Cretaceous), South Texas: ABSTRACT

The lower Glen Rose Formation in the subsurface of south Texas exhibits three cycles of shoal-water complexes, consisting of high-energy bank, bar, and biogenic reef deposits that developed on the Pearsall arch. Facies distribution shows that these elongate complexes trend northeast-southwest for at least 78 mi (125 km) and are located 44 mi (70 km) seaward of the Lower Cretaceous shoreline. Although barren of oil and gas, these vertically stacked cycles contain facies development and porosity preservation essential for attractive exploration targets. Each cycle represents three major depositional facies: open-marine shelf, shoal-water complex, and protected lagoon. The open-shelf facies is characterized by terrigenous mudstone to wackestone. The shoal-water complex consists of skeletal and oolitic grainstone surrounded by lower energy packstone deposits. High-energy patch reefs of coral, stromatoporoid, and caprinid boundstone cap the grainstones. Lagoonal deposits of low-energy wackestone and laminated mudstone overlie each of the shoal-water sequences and indicate seaward progradations, which were interrupted by transgressions of open-marine shelf deposits of the succeeding cycle. The high-energy patch reefs may have prograded seaward across the shelf as the initial build-up of the Stuart City shelf margin. Diagenesis during burial has resulted in loss of porosity in the rocks. The greatest remaining porosity occurs in the grainstone facies. There are two major porosity types: primary interparticle and secondary moldic. The primary porosity resulted from early meteoric cementation and preservation of high initial interparticle pore space prior to extensive grain compaction. The secondary porosity is the result of aragonite allochem dissolution. End_of_Article - Last_Page 1424------------

Ecostratigraphic Model for Shelf Platform Development of Middle Cretaceous (Stuart City) Limestones of South-Central Texas: ABSTRACT

ABSTRACT A new shelf platform model is developed for the Middle Cretaceous strata of South Central Texas based on an ecostratigraphic basin analysis. The concept of ecostratigraphy integrates the various ecologic parameters along time planes so that sequential distribution of magnafacies is observed. Analyses of the Stuart City Trend and associated facies suggest that the shelf platform is formed in a subsiding basin and is developed in two stages. The first involves a platform stage, the second a vertical stacking stage. Shelf platform development is a continuous process beginning in the ramp limestones assigned to the lower Glen Rose Formation. These Trinitian carbonates develop barrier reefs and prograde across the shelf. The debris slope at the base of the barrier reefs forms an elevated platform which maintains the reef organisms within their preferred shallow-water habitat and above the relatively deeper waters of the shelf. When the debris slope reaches the early Fredericksburgian shelf edge, that is maintained by the continental slope, the material is carried beyond the point of stabilization of the debris slope and moves down the continental slope to the abyssal plain. Progradation ceases but barrier-reef development continues and forms a near vertical zone of barrier reefs associated with the continental shelf edge. The barrier trend, which is created at the close of the platform stage, forms the base upon which vertical barrier growth is initiated. In this region, the vertical stage is formed during the Fredericksburgian, continues into the Washitan, and develops as a result of stretched, upward-shoaling cycles.

Contrasts in Cementation, Dissolution, and Porosity Development Between Two Early Cretaceous Reefs of Texas: ABSTRACT

The influence of cementation and dissolution on porosity is investigated by comparing two reefs with significantly different diagenetic histories. Reefs of the subsurface Sligo Formation in South Texas are buried to depths of 15,000 to 20,000 ft in a narrow belt along a shelf edge of regional extent. Cores from five wells distributed along 225 miles of the shelf edge show that porosity in the reef and backreef facies is persistently occluded by (1) radiaxial fibrous calcite, a cement whose origin appears to be related to the replacement of a synsedimentary marine cement, and/or (2) coarse calcite mosaic, a cement introduced later in the diagenetic sequence during a time of basin subsidence. Calcite cements of this type and sequence have also been reported to be detrimental to porosity in other ancient shelf-margin reefs. Therefore, the creation of porosity in shelf-margin reefs may depend on processes (dolomitization, fracturing, dissolution) which can offset the influence of cementation. In contrast to the Sligo, large patch reefs in the outcropping lower Glen Rose Formation in south-central Texas record a simpler diagenetic history which preserved porosity. One reef, selected for detailed study, has experienced only one phase of diagenesis—namely, early subaerial exposure which created moldic porosity and precipitated a single generation of calcite cement. After this exposure, no additional cements were introduced, despite burial beneath a few thousand feet of younger Cretaceous marine sediments and reexposure of the reef to subaerial weathering from Miocene to Recent time. Thus, the key to understanding porosity preservation in theGlen Rose reef lies in the role of paleohydrologic and geochemical conditions during burial and reexposure of the reef. Whether this can be predicted is a matter for future research. 'Atlantic Richfield Company, Dallas, Texas LOWER CRETACEOUS STRATIGRAPHIC MODELS FROM TEXAS AND MEXICO T. A. Bay, Jr

The Pickton Field - Review of a Successful Gas Injection Project

Abstract The Pickton field Bacon Lime reservoir, with its thin section, high drilling costs, low relief, high shrinkage oil and dissolved-gas-drive producing mechanism presented a challenge to improve recovery efficiency and provided the opportunity for a reasonable margin of profit where primary operations might have ended in economic failure. Reservoir studies indicated a recovery of only 6.6 million of the 34 million STB oil in place by primary operations. Cooperation of royalty owners and operators at a time when unitization was in its infancy and its legal status was uncertain made possible an increase in recovery to 22 million bbl, including the gasoline plant products. Introduction The Pickton field was recognized early as a prime prospect for the application of reservoir engineering technology because of the extremely low recovery anticipated as a result of a number of unique reservoir characteristics. Of added incentive was the prospect of a large and irrevocable loss of oil if primary operations were conducted to their usual economic limit. This presented a challenge to the operating and royalty interests in the field because at that time, the late 1940's, unitization was in its infancy and many operators were concerned over the possible legal problems involved. Most cooperative ventures were directed toward reservoirs substantially depleted of their primary reserves where incentives were clearly defined. Also Article 6008b, relating to voluntary unitizations, was not passed by the Texas legislature until 1949. History of Development In Nov., 1944, with the completion of Humble's C. D. Nichols, initial production was obtained from the Pickton field in the East Texas basin located in the northeast corner of the state. The presence of the reservoir had first been indicated by geologic correlation of subsurface data and was later confirmed and isolated by geophysical data. Structurally, Pickton is an extremely low-relief anticline which, of itself, is not unusual for small structures in the East Texas basin. The unique feature of Pickton is the structural low relief in a field large enough to contain 34 million STB oil and to extend over an area in excess of 7,300 surface acres. It has a dip which varies between 1/2 and 1 1/2 degree as indicated by the structure map of the reservoir, Fig. 1. The producing reservoir known locally as the Bacon Lime is a usually non-productive, low porosity, calcareous, oolitic zone occurring at a depth of about 7,900 ft The field is in the upper portion of the Rodessa member of the Lower Glen Rose formation and underlies the Massive anhydrite zone throughout a large part of the East Texas basin. The saddle-like configuration of the reservoir is shown to an exaggerated vertical scale in Fig. 2, as a northwest, southeast cross-section through the original production area and the extension of the field. The western area of the field was first developed with 57 wells being drilled. The final stage of development began after the discovery of a productive formation more than a mile to the east of the limits of production in the original development area. Until development of this extension area began 5/2 years after completion of the discovery well, and showed considerably more original oil in place, the exact producing mechanism of the field was not definitely known. The preponderance of geological data indicated dissolved-gas drive, but performance persistently exceeded predictions. Eventually the field was fully developed when a total of 166 producing wells had been drilled on 40-acre spacing, and the boundaries of production had been defined by a permeability pinchout to the north and east and by a water table at 7,425 ft subsea to the south and west. JPT P. 399ˆ

Central Texas Lower Cretaceous Stratigraphy: ABSTRACT

The Trinity Group is divided into a lower unit consisting of the terrigenous Hosston Formation overlain by the carbonate Sligo; a middle unit called the Pearsall, made up of the Hammett shale, Cow Creek limestone: and Bexar shale; and an upper unit which includes the Hensel sand, overlain by the Glen Rose limestone. Limestone, dolomite, and marl of the section between the base of the Upper Trinity and the top of the Edwards were deposited in shallow water behind the Stuart City coral-rudistid barrier reef. Lower Glen Rose reefs and the Stuart City reef formed the southwestern, southern, and eastern barriers of the Ferry Lake anhydrite evaporation pan. The Fredericksburg Group includes the strata between the base of the Bee Cave limestone and the base of the Kiamichi. The Washita Group includes the Kiamichi, middle (Kiamichi) Edwards, upper Edwards, Georgetown, Del Rio, and Buda formations. The upper, or the lower Edwards should be renamed. Structural elements which affected Lower Cretaceous deposition include the spasmodically positive Belton high (new term), the Round Rock syncline (new term), two synclinal troughs behind the Stuart City reef, and the Sample fault system (new term). Up-to-the-coast faults are dominant southeast of the axes of the synclinal troughs, and down-to-the-coast faults are dominant northwest. End_of_Article - Last_Page 1967------------

Performance of the Pickton Field

Abstract The Pickton field, located in Hopkins County, Tex., produces from the Bacon lime reservoir of the Lower Glen Rose formation. The discovery well initially produced 50.2 API gravity oil with a gas-oil ratio of 1,350 cu ft/bbl, and subsurface samples of the reservoir fluid obtained soon after completion showed that the Pickton crude is unique in that it has an extremely high dissolved gas-oil ratio and is subject to very severe shrinkage. Reservoir studies indicated a recovery of only 19.4 per cent of the oil originally in place during primary depletion by dissolved-gas drive. It was also estimated that pressure maintenance recovery by gas displacement would total 36 per cent of the oil originally in place. Pressure maintenance by injection of dry Pickton field gas and extraneous gas from the Yantis field has increased the reservoir pressure to 90 per cent of the original pressure, and a satisfactory gas-sweep pattern has been maintained. Current recovery is 35 per cent of the oil in place. In this high-pressure gas injection pressure maintenance project, it is believed that vaporization of reservoir oil by dry gas injection has contributed substantially to the total ultimate recovery. Introduction The Pickton field history has been sufficiently short so that the predictions obtained by extensive engineering studies have been evaluated. Analysis of the results indicates, that by maximum use of advanced engineering technology and present day conservation measures, the Pickton field operations have been converted from an unprofitable to a profitable enterprise. In Nov., 1944, with the completion of Humble's C. D. Nichols 1, initial production was obtained from the Pickton field in the East Texas basin, which is situated in the northeast corner of the state as shown at the top of this page. A large scale man of the central area of this basin. Fig. 1, locates the Pickton field in Hopkins and Franklin counties, 28 miles southwest of the Talco field and 28 miles northwest of the Hawkins field. The field is 16 miles southeast of Sulphur Springs, Tex.

Nummoloculina in Lower Cretaceous of Texas and Louisiana

Several occurrences of the miliolid Nummoloculina in the Lower Cretaceous of Texas (lower Glen Rose through upper Devils River limestones) and one occurrence in the Lower Cretaceous of northern Louisiana (lower Glen Rose limestone) are reported for the first time. The geologic range of Nummoloculina as ascertained by the writers is Lower Cretaceous to Recent. Nummoloculina limestones in Texas are here reported from the upper Devils River limestone (Georgetown limestone equivalent) in Val Verde County and the Edwards limestone in La Salle and Maverick counties. Nummoloculina occurring in the Devils River limestone in Val Verde County is figured and discussed. Nummoloculina from the El Abra miliolid member of the El Abra formation of northern Mexico (Lower Albian through Lower Cenomanian) is figured for comparison. The uppermost Devils River limestone and the upper El Abra miliolid member are compared, but no correlation is implied. Following Norton's zonation of foraminifers, miliolid limestone environments would correspond most closely with his Zone A where the water is 0-5 fathoms deep and the temperature is 21°-32°C. Miliolids occurring in abundance are facies foraminifers characteristic of back-reef and inter-reef environments; therefore, they are useful in paleoecology. Although miliolid limestones in Texas vary in age within, but are restricted to the Lower Cretaceous (Sligo through upper Devils River limestones), they may be of local or regional value in the differentiation of large stratigraphic units within the Sligo through upper Devils River limestones. Miliolid limestones are used successfully in parts of southwest and central Texas to mark the faunal top of the Edwards limestone. However, in the Devils River area, or in any other area where reefs were formed in Washita as well as Fredericksburg limestones, such differentiation based on miliolids is unsatisfactory.

Performance Characteristics of a Volumetric Condensate Reservoir

Abstract The performance history of a volumetric gas condensate reservoir ispresented. Curves depict the pressure-production relation and illustrate thephase behavior of the reservoir fluid. This performance is compared tocalculated performance. This Bacon Lime Reservoir was discovered in 1941 and has been produced tofield separators and gas sales. Reservoir performance has been observed byperiodic bottom hole pressure surveys and companion sample analysis of welleffluents, in addition to gas and condensate production data. The pressure-production history demonstrates that the reservoir has producedunder volumetric control. The "retrograde" behavior of the reservoirfluid is illustrated by decreasing butanes-plus content of the well effluent, followed by revaporization as the reservoir pressure approaches abandonment.Calculated performance predictions are compared to actual performance and somediscussion offered on apparent discrepancies. Introduction Since the late 1930's, many gas condensate reservoirs have been developed, the retrograde theory of phase behavior has been generally accepted, and anumber of cycling programs have been initiated. Numerous technical papers havesince appeared in the literature dealing with the theory and application ofcycling the gas condensate reservoirs. Some cycling operations have nowadvanced to a stage where it is possible to determine performancecharacteristics to a fair degree of accuracy. Field performance data for gas condensate reservoirs operated by pressuredepletion have not been so extensively reported in the literature, althoughtheir probable behavior has been discussed in explanation of the retrogradetheory. It is the purpose of this paper to compare calculated theoreticalreservoir performance with field observations and well stream analyses whichhave been obtained throughout the practical producing life of a smallvolumetric gas condensate reservoir. The reservoir under study is the Bacon Lime Zone of a field located in EastTexas. The Bacon Lime occurs in the Lower Glen Rose Formation of CretaceousAge. T.P. 2708

A Study of Oil and Gas Conservation in the Pickton Field

Abstract This paper presents the results of a complete reservoir study designed todetermine a sound economic program for the conservation of oil and gas in thePickton field, Hopkins County, Texas. The Pickton field produces from the BaconLime with all indications of the study being that production is predominatelyby dissolved-gas drive. Calculations of the total ultimate recovery to beexpected under primary operations indicated only 16.7 per cent of the oiloriginally in place would be recovered. This unusually low recovery is due tothe type of drive operating and the extremely high dissolved gas-oil ratio andshrinkage. Results are presented for six plans of returning gas to the reservoir, evaluated to determinecomparative recoveries and economics ofreturning gas at a constant rate by supplementing Pickton gas with extraneousgas during the early portion of the operation, andconventional gas-returnoperations without using extraneous gas, andthe optimum size of compressorplant for each type of pressure maintenance. The over-all economic program considers, for either type pressuremaintenance operation, a gasoline plant to process the unusually richcasinghead gas. Since pressure maintenance will disturb equities, pooling ofroyalties is in the case of Pickton a prerequisite to conservation of oil bythis type of operation, both from an economic and legal standpoint. In theevent pooling of royalties cannot be achieved, the study considers a gasolineplant to operate under a modified primary production operation which will makethe conservation of gas possible. Introduction The Pickton field, located in Hopkins County, Texas, was discovered inNovember, 1944, by the completion of Humble's C. D. Nichols 1, in the Baconlime of the Lower Glen Rose formation, through perforations from 7,888 to 7,896feet. The well initially produced 50.2 API gravity oil with a gasoil ratio of1,350 cubic feet per barrel. Subsurface samples of the reservoir fluid obtainedsoon after completion of the discovery well showed that the Pickton crude isunique in that it has an extremely high dissolved gas-oil ratio and is subjectto very severe shrinkage. T.P. 2564

Developments in East Texas in 1946

Eight new oil-producing areas and 4 new gas-producing areas were discovered in East Texas during 1946. Three of the new oil discoveries produce from the Woodbine formation. These are North Gallatin and William Wise in Cherokee County and Norman Paul in Wood County. Oil production in the sub-Clarksville sand of the upper Eagle Ford was also discovered in the Norman Paul field. Production in the South Flynn field in Leon County is considered to be from an undifferentiated Woodbine-Eagle Ford section. Two of the new oil discoveries produce from the Paluxy formation. These are Boynton and Mt. Sylvan, both situated in Smith County. Two new oil fields were discovered in the Travis Peak formation, namely, Elysian Fields in Harrison County and Lassater in Marion County. The four new gas-producing areas are Pine Hill and South Henderson in Rusk County, which produce from the Travis Peak; Flower Acres in Bowie County, which produces from the Smackover, and Huxley in Shelby County, which produces from the Pettit zone of the lower Glen Rose. During the year, new producing zones were discovered in 6 older fields. Exploratory drilling was characterized by a continuation of the trend toward deeper drilling which has been in progress for several years.

Developments in East Texas During 1945

One new oil-producing area and four new gas-producing areas were discovered in East Texas during 1945. The LaRue area in Henderson County produces oil from the Bacon limestone member of the Rodessa section. The gas-producing areas include Stony Point in Freestone County and Marshall in Harrison County, both of which produce from the Pettit section; Fairfield in Freestone County which produces from the Woodbine and Travis Peak, and Whelan in Harrison County which produces from the Rodessa and Travis Peak. Deeper drilling in old fields resulted in the discovery of new oil-producing zones in two fields and new gas-producing zones in two additional fields. Shallow oil was found and produced in two old fields. Exploratory drilling in East Texas was again characterized by deeper tests having the Paluxy, lower Glen Rose, Travis Peak, Cotton Valley, and Smackover formations as their principal objectives. Woodbine exploration was extended into the southern part of the East Texas area.

Developments in East Texas in 1943

Four new oil-producing areas and two new gas-producing areas were discovered in East Texas in 1943. Of the new oil areas, two produced from the Paluxy formation, one from the Pettit zone, and one from both the Rodessa and Pettit zones of the lower Glen Rose formation. One of the new gas areas produced from the Woodbine, the other from the Pettit zone of the lower Glen Rose. Exploratory drilling in East Texas was characterized in general by deeper drilling than in the past, most of the important tests having the Paluxy, lower Glen Rose, Travis Peak, and Smackover formations as their objectives.

Developments in East Texas in 1942

Five new oil fields, one oil and gas field, and one gas field were discovered in East Texas in 1942 Three of these discoveries produce from the Woodbine formation, two from the Paluxy formation, and two from the lower Glen Rose formation. There was a decline of approximately 70 per cent in the number of wells drilled in producing areas. Important exploratory tests were directed to the Wilcox, Woodbine, Paluxy, lower Glen Rose, Travis Peak, and Smackover formations.

Developments in East Texas During 1941

The marked increase in exploratory tests in East Texas during 1941 resulted in the discovery of three oil fields. Two of these fields are producing from the Woodbine formation and one from the Rodessa zone of the lower Glen Rose formation. In the Hawkins field, which was the major 1940 discovery, a rapid development program took place and 243 oil wells, 3 gas wells, and 8 dry holes were drilled. The number of completions in other proved fields exceeded that of 1940.