Oligocene Sands Research Articles

Depositional and Diagenetic Controls on Gas Production from Frio (Oligocene) Sands at Monte Christo Field, Hidalgo County, Texas

ABSTRACT Monte Christo Field is located in central Hidalgo County on the Gulf Coastal Plain of south Texas. Depositional and structural factors controlling the accumulation and production of hydrocarbons are related to lateral and vertical facies changes as well as syndepositional growth faulting. These factors combine to compartmentalize the pay sandstones into discrete, isolated reservoirs. Rollover into these growth faults, coupled with greater sandstone thickness and quality at preferred points of delta-front sand deposition, result in a combination of structural and stratigraphic entrapment of gas. Frio reservoir sandstones consist of stacked, upward-coarsening, progradational packages. In each is found a vertical succession of basal abandonment facies, offshore mudstones, distal-delta front sands and silts (lower shoreface), and distributary mouth bar (upper shoreface) sandstones. The upper shoreface sandstones comprise the best reservoir facies. Each facies contains trace fossils indicative of the paleo-environment. Cyclic progradational packages at Monte Christo Field are the direct result of episodic movement along the Mission fault, a large down-to-basin growth fault which bounds the field to the west and parallels depositional strike. Within the study area, three smaller splinter faults bifurcate to the east from the Mission fault and compartmentalize the Frio reservoirs. Diagenetic influences on reservoir quality involve extensive cementation and secondary porosity generation. Reservoir sandstones are fine- and very fine-grained feldspathic litharenites and lithic arkoses. The breakdown of unstable volcanic rock fragments results in significant chlorite and illite grain-coating cements which commonly block pore throats and greatly reduce permeability. Calcite and ferroan carbonate cementation occludes porosity significantly. Minor quartz, potassium feldspar, zeolite and titanium oxide authigenesis are also present. These factors result in relatively low porosities of 10 to 15% and very low permeabilities. The generation of secondary porosity by dissolution of feldspars and carbonate material enhances the diminished pore volume. Point counts reveal that a minimum of 30% of the existing porosity is of secondary origin. Even with significant porosity enhancement in some intervals, artificial fracture stimulation is required to achieve an economic rate of production. This procedure also taps into the substantial quantities of gas trapped in the lowest permeability portions of the reservoir facies.

Depositional and Diagenetic Controls on Gas Production from Frio (Oligocene) Sands at Monte Christo Field, Hidalgo County, Texas: ABSTRACT

Depositional and Diagenetic Controls on Gas Production from Frio (Oligocene) Sands at Monte Christo Field, Hidalgo County, Texas: ABSTRACT

L'apport des mineraux opaques a l'etude des paleoalterations: Exemple de quelques sables tertiaires de haute Belgique

L'étude en lumière réfléchie de concentrés de minéraux denses des sables oligocènes des Hautes Fagnes et de la région de Liège (Belgique) met enévidence les phases successives de leur altération: une réduction diagénétique marquée par les formes d'altération de l'ilménite et de l'ilménomagnétite, une sulfurisation lorsque des conditions lagunaires ont prévalu après la régression oligocène, une phase de silicification et enfin une oxydation plus ou moins intense du sédiment selon les conditions locales.

INTERIOR CAVITIES AND EXTERIOR SURFACE TEXTURE OF DETRITAL QUARTZ OF SOME EGYPTIAN CLASTIC SEDIMENTS

Cavities of freshly fractured surface and the exterior surface texture of detrital quartz grains were examined and photographed with the help of the scanning‐electron microscope at different magnifications. Three formations of Egyptian clastic sediments are used for this purpose namely: (a) Carboniferous sandstone of west‐central Sinai, (b) the so‐called Nubian sandstone of Early Cretaceous(?) age from southern Egypt, and (c) Oligocene sand accumulations from the vicinity of Cairo.It is concluded from the present study that in most cases the intracrystalline cavities have an average diameter of less than 10 microns. Different shapes can be acquired by these cavities‐ranging between irregular and negative crystal forms. The distribution of ca vities seems to be mainly along the fractures and the planes of growth but random distribution is sometimes observed.Examination of the surface features also shows that the depositional environment for Sinai and Aswan sandstones is aeolian with more effective diagenetic alteration in the first type of deposit. In the case of Cairo sandstone, the surface impressions of the quartz confirm the alluvial environment of deposition.

Hydrocarbon Exploration on Ancient Shelf-Slope Breaks: ABSTRACT

A general set of traps, reservoirs, and seals occurring on the shelf-slope break can be hypothesized based on the structural regime, provenance, and width and slope of the shelf. To evaluate this break is to look at the entire region--shelf and slope. With a wide or moderately wide shelf, gentle slope, and peneplaned provenance, carbonate sediments would dominate in marine environments. Logically, a reefal environment (reservoir) would be expected at the shelf slope. Conversely, with a narrow shelf and a positive continental borderland in close proximity, terrigenous clastics would be expected. Deltaic-like reservoirs could be expected on the shelf; turbidites would logically occur downslope. A broad shelf with a positive provenance could inspire various lithologic deposition (depending on the environment)--reefal at the shelf-slope area, deltaic or lagoonal behind, and turbidites in front. Examples of such former reservoirs are Empire-Abo reef trend of Texas-New Mexico; Cretaceous Stuart City shelf margin of Texas; Golden Lane-Pozo Rica trends of Mexico; Miocene pinnacles of the Salawati basin, Irian Jaya; and Kirkuk field on the Arabian Platform. Penultimate reservoirs are the linear sands of the San Joaquin and Ventura basins; Oligocene sands of south Louisiana; Triassic sands of the North Sea basin; Cretaceous Seaway sands in the Powder River basin; and the ancient Mississippi delta and cone. Latter reservoirs are found in the eastern shelf, Midland basin, and Bombay offshore basin, India. It is understood that for some of these reservoirs to become traps, the founding structural regime is modified, e.g., faulting, diapirism. Seals are classed as carbonate muds, evaporites, and faults. Source matter may be incorporated in marine shale and limestone deposited in anoxic environments. End_of_Article - Last_Page 946------------

Big Hill Field, Jefferson County, Texas: ABSTRACT

ABSTRACT Big Hill Field is in the Frio Sand Trend on the western flank of Big Hill Salt Dome. Multiple reservoirs in Miocene and Oligocene sands are on the downthrown side of a regional up-to-coast growth fault that expands the thickness of Lower Miocene and older sediments 57%. One Hackberry reservoir is bounded by two growth faults and an erosional surface. The hydrocarbons trapped therein are evidently indigenous to the surrounding rocks. An isopach map, Top of Frio to the Hackberry Unconformity, indicates that Big Hill salt dome was formed prior to the end of Frio time; the crest of the dome at that time was north of the present salt spine. This map also locates a buried down-to-coast growth fault that traverses the west flank of Big Hill Field but does not intersect any wells. Pressure performance histories of two reservoirs, and also of two wells not producing from these reservoirs, are shown graphically in order to illustrate the problems involved in explaining wells that are in pressure communication. Four gas-fluid contacts in a continuous Marginulina reservoir differ in elevation by 600 ±. These original gas contacts were created by hydrocarbons migrating into a complexly faulted area. Accumulation of oil downdip from these gas contacts can be reasonably explained in terms of gravity segragation effects.

Note sur le gisement d'uranium dans les sables oligocenes de Saint-Pierre (Cantal)

Abstract The uranium mineralization of the Saint-Pierre region consists of francevillite- impregnated fluviatile Oligocene sands deposited in a basin forming part of the regional Permo-Carboniferous coal-bearing trough developed in the crystalline basement complex of the Central Massif, France. The mineralization is considered syngenetic, and was probably controlled both by climatic and topographic conditions.

Peripheral Faulting at Bayou Blue Salt Dome, Iberville Parish, Louisiana

The Bayou Blue field is on an intermediate-depth salt dome, where shallow oil in Pliocene and Miocene sands was discovered in September, 1929. The initial productive area, located on the apex of the dome, was considered depleted in 1932. First significant production from Miocene sands on the west flank was established in February, 1940. This led to active development of the northwest, west, and southwest flanks of the dome and re-establishment of shallow production on the crest. East-flank production from lower Miocene sands was first obtained in 1941. Deep Oligocene sand oil was discovered in 1954 on the northeast flank, but appears to be non-commercial. Through December, 1955, 13,108,421 barrels of oil had been produced. The dome is elliptical in outline and is characterized by peripheral faulting, which generally parallels the elongate axis of the dome. These faults, which are downthrown away from the salt plug, change direction, producing an arcuate or sinuous trace on any particular datum. They may join the salt face with depth or along strike of the salt mass. The dominant peripheral fault of Bayou Blue offsets lowermost Miocene beds, which are present on the apex of the dome, to a position 4,600 feet structurally lower on the northwest flank of the dome. The major producing area of the structure is located southwest of the dome's crest on the downthrown side of this peripheral fault zone in beds of Miocene age which terminate abruptly against the steep salt face. A system of complex radial and co plementary faulting is present in the shallow beds above the apex of the plug. Contoured fault maps are included of all important radial and peripheral faults. The over-all structural aspects of the dome are illustrated by an upper Miocene (Bigenerina 3) map and a lower Miocene (Siphonina davisi) map and six electric-log structural cross sections. Nineteen typical reservoirs encountered in the Bayou Blue field are included, to illustrate the local structural conditions and productive areas.

Secondary Recovery Operations in the Tijerina No. 3 Unit Reservoir

Introduction The purpose of this paper is to present the production history of the Tijerina No. 3 Reservoir from its initial development in April, 1945, through April. 1954, including primary development, unitization, and secondary recovery by high pressure gas injection. Particular attention is given reservoir performance as influenced by the migration of fluids in a continuous but erratic sand of low permeability. It is interesting to note that, from material balance calculations, apparently little or no injected gas goes into solution with the remaining reservoir oil, even though reservoir pressure has been increased an average of 700 psi. Location and Geology The Tijerina No. 3 Reservoir is located in the southwest portion of the Tijerina-Canales-Blucher field, approximately 2 miles northeast of the town of Premont. Jim Wells County, Tex. It is the deepest member of a series of lower Oligocene (Frio) Sands productive in the field, lying at an approximate depth of 7,200 ft subsea. Structurally, the reservoir is a permeability trap lying on an erratic monocline, with an average southeast dip of 170 ft per mile. There is no faulting present to break the continuity of the sand. A structure map drawn on the top of the sand is shown in Fig. 1. The productive limits of the reservoir are defined by shale outs and dry tests except in an area to the northwest; where, due to the lack of geological control, the location of the strand line is assumed. The oil column is bounded in this area by a small gas cap, the original gas-oil contact having been established at 7,058 ft subsea by drill stem and production tests run during development. There is no evidence of a water-oil contact in the reservoir. The sand is described as being firm, fine-grained, medium to hard, with scattered shale streaks occurring near the strand line. It possesses a low and erratic permeability as substantiated by PI's which ranged from 0.020 to 0.114 in five wells when measured in April, 1948. A typical electric log is shown in Fig. 2.

Genesis of Oligocene Sandstone Reservoir, Seeligson Field, Jim Wells and Kleberg Counties, Texas

The character, distribution, and probable genesis of a typical lenticular oil-bearing sand body of the Gulf Coast Tertiary, namely, Zone 19B, an Oligocene sand of the Seeligson field, Texas, were determined for the purpose of developing and defining criteria by which such sand bodies can be readily identified and delimited in the subsurface. The stratigraphic framework was specified by cross sections, fence diagrams, isopach maps, and facies maps, prepared from electric logs and core descriptions, and the sediments were characterized by size, shape, thin-section, X-ray, differential thermal, and chemical analyses. Principal results are: (1) the isopachal trend of the sand body is nearly normal to the regional depositional strike; (2) the sand grades from medium grain at the base to fine at the top and can be divided into three zones on maximum grain size; (3) a typical specimen is a mixture of (a) well sorted sand, the framework size fraction, (b) interstitial clay, the tail of the size-distribution curve, and (c) interstitial calcite cement; (4) the mineral composition is similar to that of a Recent river sand, but dissimilar to that of beaches, of the same geological province. The sand body is probably an Oligocene alluvial-plain deposit as indicated by its similarity to such Recent deposits in external form, vertical textural zonation, colors of associated shales, mineralogy, presence of mud fragments, and absence of indigenous fauna. The often stated opinion that oil-field trends of the Gulf Coast, such as the Frio-Vicksburg, are shore-line trends has led many geologists to infer that the reservoir sands of these oil fields are strand-line deposits. The conclusions of the present study emphasize the risk of such deductions. The trends may be indirectly related to shore lines by reason of marine source beds, but many, or possibly most, of the reservoir sands may be of continental origin. The trapping in this zone arises from updip normal faulting and gentle doming of a lenticular alluvial sand body which is oriented in the direction of regional dip. The greatest value of these findings lies in the extrapolation and extension of this knowledge of local genesis to other parts of the section. In such a fashion a regional depositional and tectonic history can be outlined, centers of deposition for various geologic ages can be delimited, and areas favorable for the presence of permeable beds and oil accumulation can be approached.

Geology and Development of Poza Rica Oil Field, Veracruz, Mexico

The Poza Rica field is the most important producing structure in Mexico. On the surface this structure is reflected in upper Oligocene clays, sands, and lenticular limestone of the Coatzintla formation. This structural nose dips east-southeast and becomes more accentuated in the subsurface down the stratigraphic column until the Tamabra limestone is reached. This limestone is Albian-Cenomanian in age and production comes from a porous facies that crowns the axial zone. It is proposed that the structure was a tectonic high during Tamabra time, whence the origin of the reef facies. The reduced section of Mendez shales and San Felipe limestone formations above the Tamabra is suggested as diagnostic of the presence of reef facies for future Tamabra tests in the Tampico Embayment. This structure is producing approximately 100,000 barrels per day and has an accumulated production of approximately 8,943,167,855 cubic meters of gas and 50,754,198 cubic meters of oil to August, 1948. Some considerations are made regarding future developments and commercial disposal of the gas produced.

Les bryozoaires du forage des Eyquems a Merignac (Gironde)

Abstract Describes bryozoans (including one new genus and several new species) from Rupelian (Oligocene) sands traversed by a boring at Merignac, Gironde, France.

Presence de foraminiferes dans la meuliere de Beauce [with discussion

Abstract Reports the occurrence of foraminifers in the Beauce millstone formation capping Stampian (Oligocene) sands of the northern and central Paris basin, France. The foraminifer fauna of the formation, previously described as a lacustrine deposit on the basis of included fresh-water macrofossils, is generally indicative of deposition in a shallow warm sea. The foraminifers therefore probably represent forms which were introduced during marine invasions of the dune areas of the Stampian sea coast and which adapted to the conditions obtaining in the lake basins.

Crocker Flat Landslide Area, Temblor Range, California

The Crocker Flat landslide, located in the vicinity of Recruit Pass and northwest of Fellows, is composed largely of lower Miocene and Oligocene sands and silts and a minor amount of middle Miocene shale which were superimposed upon, and subsequently infolded with, younger Miocene sediments. This landslid mass descended by gravity, in upper Miocene time, from a highland located within or west of the San Andreas Fault zone, prior to the deposition of the Santa Margarita (upper Miocene). During Santa Margarita time coarse clastics derived from crystalline rock masses west of the Temblor Range were deposited unconformably over the Crocker Flat landslide and adjacent areas. The Santa Margarita beds and the Crocker Flat landslid mass were involved in the post-Miocene orogeny w ich elevated the Temblor Range and folded and faulted both of these units. Infolded and downfaulted outliers of Santa Margarita, on top of the Range, have been preserved from later erosion. On the summit of the Range clastics so coarse that they have been mapped as Basement complex by several workers are considered to be Santa Margarita in age because they are intertongued with and grade laterally into sands and boulder beds containing Santa Margarita fossils in adjacent areas. Furthermore a portion of the landslid lower Miocene and Oligocene sediments of the Crocker Flat area are unconformable beneath these coarse clastics. This relationship also tends to preclude the premise of this so-called basement being a part of a huge overthrust sheet. The crystalline rocks previously mapped as Basement complex on the west side of the Range are not in place but are detrital in origin and of Santa Margarita age also; these sediments owe their coarseness to a proximity of source and to possible minor landsliding during deposition. The intercalated lenses of granitoid and schistose boulders and sands in the upper Miocene punky shales on the northeast side of the Temblor Range are equivalent in age to the coarse Santa Margarita conglomerates on the southwest side of the Range. These beds are believed to have had a common western source which must have been near at hand, within or west of the San Andreas Fault zone. The erosional remnants of Santa Margarita conglomerate along the summit and higher parts of the Temblor Range are regarded as being normally depositional in origin and not klippen remnants of an overthrust sheet; these deposits represent an intermediate facies between the interbedded conglomerate and punky diatomaceous Santa Margarita on the northeast and the coarse conglomerates on the southwest side f the Range. The Recruit Pass fault is a normal fault with its western side downthrown; it is thought to be one of the lines along which uplift occurred to give the present elevation of the Temblor Range.

Oil and Gas Possibilities of France

Nearly the entire oil production of France comes from Oligocene sand lenses in the Pechelbronn field in the Department of Bas-Rhin, Alsace, where it has been mined for many decades by means of shafts and galleries in addition to being recovered in recent years from wells. A total production of 12,210,000 barrels (1,720,209 metric tons) had been extracted from the field up to January 1, 1931. A relatively small amount of oil (19,038 metric tons or 141,600 barrels) has been extracted at Gabian, Department of Herault, in southern France, where Triassic strata constitute the producing formation. A few barrels have been obtained by drilling in a graben in the Limagne (Auvergne) where large asphalt seepages are found surrounding volcanic necks in Oligocene sediments. Numerous a phalt seepages also exist in Triassic rocks throughout a belt paralleling the Pyrenees Mountains in the extreme southwest. Natural gas emerges from various Mesozoic and Tertiary strata in and near the southern extremity of the Jura Mountains, where the village of Amberieu has been supplied with gas for years from several wells drilled near Vaux-en-Bugey (Vaux-Fevroux). Bitumen-impregnated sandstones of various ages are found in a belt along the east flank of the Jura. Although France contains several sedimentary basins in which possibilities of commercial oil exist, the tectonic conditions are in general complicated in the vicinity of the best indications. A vast amount of geologic work, and of geophysical work geologically directed, will be necessary in order to make discoveries, but ne fields of commercial importance may ultimately be found.

Deep Sand Development at Barbers Hill, Chambers County, Texas

The writers describe the development of this dome since 1924, which is the final date of the original article on this field by George Bevier. Barbers Hill is a large shallow salt dome located in the Texas Gulf Coastal Plain in the general vicinity of other productive salt domes. Oligocene sands have yielded wells of the gusher type from a 5,100-foot sand horizon for the past 15 months, after years of unprofitable exploration of shallower sands. A 10,000-barrel well from a depth of 6,416 feet on an undeveloped flank of the dome in a deeper horizon in a formation probably of Oligocene age indicates a new stratum, richer than those already found. Seventy-one deep producing wells have been drilled during this recent period. The total production for 1929 was 4,487,000 barrels. An exceptional condition is found on the northeast flank of the dome, where several hundred feet of cap rock and salt between the depths of 1,500 and 2,500 feet jut out from the main intrusive mass. Many wells have drilled through this and have found the sedimentary beds below, including oil sands, practically undisturbed by this overhanging mass. The general characteristics of the dome and flank formations are indicated by several cross sections. A map of the field shows the approximate inside limit of production. Production records and well histories are shown by graphs and tables.

Recent Work of Geological Surveys

IV.—THE UNITED STATES. THE United States Geological Survey frequently assists research by publications in which definite subjects are dealt with from a comprehensive point of view. The Bibliography of North American Geology for 1906 and 1907 was issued in 1909. A bibliography of Archaean and Algonkian geology, divided up under the various States, is given in Bulletin 300 (pp. 940, 1909), in which Messrs. Van Hise and Leith review the pre-Cambrian geology of North America. As the title shows, Canada is included, and the summaries given of published work make this volume welcome in every library of scientific reference. Bulletin 364 (1909) is by Messrs. Darton and Siebenthal on the Laramie basin in south-eastern Wyoming. The name Casper formation is proposed (p. 13) for Carboniferous limestones and sandstones resting on pre-Cambrian rocks on both sides of the Laramie Range. The Laramie beds, over which much discussion has arisen, may be represented by the highest sandstones and shales of the Cretaceous Montana series, and an unconformity, now widely recognised, occurs between this series and the Cainozoic beds (pp. 35 and 43). The Laramie question, it may be observed, has been recently discussed by Mr. Whitman Cross (Proc. Washington Acad. Sci., vol. xi., 1909, p. 27), who proposes the name Shoshone Group for the beds elsewhere styled Laramie, but lying above the unconformity. The coloured geological map in the memoir, and the illustrations, show well the character of the broad valley of the Laramie, with its floor 7000 feet or more above the sea,.and gneissic hills rising some 3000 feet higher on the east and west (Fig. 1). Interesting contrasts are afforded in a great variety of strata, especially where Oligocene sands form level ground in hollows of the Archaean rocks of the Laramie range.