Sandstone Geometry Research Articles

Sedimentology and Mineralogy of Suffield Heavy Oil Sands (Lower Cretaceous), Southeastern Alberta: ABSTRACT

The Suffield heavy oil sands are found in the glauconitic sandstone of the Mannville Group in two major north-south-trending sand belts ranging in thickness from 15 to 20 m. The study area is centered around a heavy oil pilot site which is a joint venture operated by Alberta Energy Co., Alberta Oil Sands Technology and Research Authority, Dome Petroleum, and Westcoast Petroleum. At this location, the glauconitic sandstone is a 46-m thick, uninterrupted sandstone partly saturated with 13° API oil. The sandstone geometry, and the sequence of lithologies and sedimentary structures, indicate deposition in a prograding shoreline beach environment. An upward transition of facies from lower and middle shoreface sands, through foreshore, to backshore, marsh, and continental eposits, is represented. The sandstone is composed of quartz, chert, sedimentary rock fragments, trace amounts of feldspar, and 2 to 30 wt. % clay. Kaolinite, the dominant clay mineral, occurs as (1) small platelets forming grain linings and pore bridges, (2) vermicular growths, and (3) silt-sized rock fragments. Lesser amounts of illite, smectite, and mixed-layer clays occur as ridges on grain surfaces and as pore bridges. Illite can also occur as needlelike projections. The most argillaceous sands, located at the top of the sandstone unit, contain only very fine-grained kaolinite. Quartz overgrowths contribute to porosity reduction in the cleaner sands. Minor amounts of secondary porosity can be identified by the presence of partly leached feldspar grains. End_of_Article - Last_Page 636------------

Gray Sandstones (Jurassic) in Terryville Field, Louisiana--Basinal Deposition and Exploration Model: ABSTRACT

Deep (~ 13,000 ft, 4,000 m) hydrocarbon production at Terryville field is from various zones within Upper Jurassic siliciclastics that are referred to informally as the gray section. This sequence of interbedded sandstones and shales occurs in the Smackover section or within the lower Bossier shale seaward of the Upper Jurassic shelf edge, and is correlative to and coeval with inner shelf facies deposited north of the field area. The Gray section at Terryville field consists of at least four sandstone bodies separated by black shales and silty to sandy shales. The shales are thinly bedded and harbor a locally abundant ichnocommunity of Chondrites, Planolites, and Scalarituba; small ammonoids and bivalves are present locally in these beds. Thin layers and lenses of sandstones (lenticular and flaser bedding, partial Bouma sequences) are intercalated with the shales locally, and commonly are heavily bioturbated by Teichichnus and Arenicolites. The sandstones are fine grained, feldspathic sublitharenites, locally conglomeratic (shale clasts), with rare ooids and comminuted skeletal fragments. The four sandstones in the field area are of stacked, lobate geometry. The lobes consist internally of anastomosing lense of sandstones and conglomeratic sandstones interbedded with and replaced laterally by shales and sandy shales. The long axes of these lobes and lenses are oriented normal to regional upper Smackover shelf-edge trends. Stacked are recognized within each sandstone lobe. These packages consist internally of repetitive second-order sedimentation units, including partial Bouma sequences, locally conglomeratic graded beds (normal and reverse), massive textureless beds, and coarse rhythmites. The thickness and internal grain size of these component units have a tendency to decrease systematically upward from the base of and laterally within each megasedimentation package. Stacked packages within and immediately surrounding the depoaxes of each lobe coarsen upward f om repetitive units of sandstones to conglomeratic sandstones. The areal distribution, vertical stratigraphy, geometry, bedform characteristics, and texture of the Gray sandstones, and their regional relation to upper Smackover carbonate facies to the north, suggest their formation as progradational submarine-fan complexes deposited in a basinal environment. The sandstones and conglomeratic sandstones are interpreted as braided distributaries and associated facies deposited in upper and midfan environments. At distances from these distributaries, the thinner sandstone packages and the interbedded shales and sandstones represent proximal overbank to midfan deposits. The intervening shales are interpreted as basin plain and distal overbank deposits. Although trapping at Terryville field is mainly structural, sandstone trends and geometries control reservoir occurrence, and this aspect of stratigraphic entrapment should be expected in future Gray sandstone fields in this area. Reservoir permeabilities in the Gray sandstones are limited because of the presence of pore-filling chlorite, illite-smectite, and dolomite. End_Page 1432------------------------------ The pore system is almost entirely of secondary origin, having resulted from the partial dissolution of labile framework grains and carbonate cements. The most effective stimulation of these reservoirs appears to be an acid-enhanced hydraulic fracture. End_of_Article - Last_Page 1433------------

Diagenesis of Frontier Formation, Moxa Arch, Wyoming--Function of Sandstone Geometry, Texture, and Composition of Fluid Flux: ABSTRACT

The lower Frontier Formation, Moxa arch, Wyoming, consists of sandstones and mudstones deposited in a wave-dominated delta and strand-plain system which prograded into the western margin of the interior Cretaceous seaway. Depositional environments in this system were offshore marine, marine sand ridges, marine shoreline, distributary channel, fluvial, and flood basin. Sediment from the Sevier orogene was sorted into different compositional and textural assemblages in depositional environments with different energies. Because of original differences in physical and compositional characteristics, diagenesis proceeded along different paths in different facies. The most important facets of original detrital composition affecting diagenesis are original clay content and the mo ocrystalline quartz/chert ratio. Diagenesis was also very sensitive to fluid flux. Sedimentary textures and sand-body geometries were important controls of fluid flow during dewatering. In the southern part of the study area, erosion eliminated the shoreline interval leaving only thin fluvial sandstones overlying offshore marine rocks. To the north, the shoreline facies was not eroded and the sandstone interval is thicker. On the assumption that sandstones received the discharge from equal volumes of shale, the thinner fluvial sandstones to the south experienced a far greater throughput per unit volume of sand and a higher rate of flow than did the thicker combined fluvial and shoreline sequence to the north. As a result, the southern sandstones are extremely porous and permeable and show signs of extensive leaching, whereas in the north there is more evidence of in-situ reactions resulting in the development of abundant authigenic and neomorphosed clays. Here, porosity and permeability are poorer. End_of_Article - Last_Page 635------------

Deltaic Cherokee Sandstones of Central Oklahoma: ABSTRACT

Exploration for delta reservoir sandstones on the Mid-Continent craton can be enhanced by a better understanding of facies character, depositional environments/processes, and factors that controlled their distribution. Appreciation of the dynamic nature of deltaic sedimentation permits the geologist to predict more precisely the stratigraphic relations and sandstone geometry. It also enables the explorationist to predict areas or trends that may previously have been overlooked. A detailed, subsurface stratigraphic study of the Cherokee sandstones (early Desmoinesian) in central Oklahoma (including parts of Lincoln, Logan, Oklahoma, Cleveland, and Pottawatomie Counties) gives insight into the processes of deltaic sedimentation which should provide help in local exploration and development operations, and in regional exploration in similar rocks encountered throughout the world. Interpretations will be based on core analyses, examination of well cuttings, study of regional and detailed stratigraphic cross sections, and analysis of structure, paleotopographic/paleodrainage, paleogeologic (subcrop), and isolith maps of several key horizons. End_of_Article - Last_Page 1016------------

Hydrogeology of the Gallup Sandstone, San Juan Basin, Northwest New Mexico

ABSTRACTComparison of the hydrologic and geologic characteristics of the Gallup Sandstone (Late Cretaceous) has shown that its aquifer properties, the movement of its ground water, and the variation in its water quality are subject to considerable geologic control. This control is imposed mainly by the distribution of seven progradational sandstone bodies which make up the Gallup. These fluvial and marine sandstone bodies were deposited along the shore of a northeast‐regressing sea. The two transmissivity zones recognized have the same trend as that of the upper marine sandstone bodies (northwest‐southeast), and transmissivity decreases northeast of the pinch‐out of the lower marine sandstone bodies. Ground‐water flow is variously controlled by geologic structure, the geometry and orientation of the marine sandstones, and the position of the northeast limit of the Gallup Sandstone. Concentration of dissolved solids, as reflected by specific conductance, is controlled in part by distance from recharge area and in part by the distribution of transmissivity. The types of geologic control determined for the Gallup should apply to other Cretaceous, marine‐sandstone aquifers in the San Juan Basin, and, in a general way, to ancient shorezone deposits elsewhere.

Geometry of Shelf Sandstone Bodies in Shannon-Equivalent Sandstone in Northern Black Hills, Montana and South Dakota: ABSTRACT

The Groat Sandstone Bed of the Gammon Member of the Pierre Shale (Campanian), equivalent to the Shannon Sandstone Member of the Steele Shale of Wyoming, crops out on the north flank of the Black Hills, where it has been mapped. Subsurface studies in Carter County, Montana, reveal a 3,900 sq km area in which sandstone thickness exceeds 23 m. This area of sandstone includes two small elongate lenses in T6 and 7S, R54 and 55E. The lenses trend northwest and are approximately 16 km long and 6 km wide. In adjacent outcrops, sandstone grades downward and laterally to the northeast into siltstone and then to shale. Sandstone units are less than 15 m thick; near the base they are fine-grained and mottled with clay grading upward into bioturbated medium to fine-grained sandstone, hich then grades upward into medium to coarse-grained sandstone with large-scale, trough cross-bedding. The Groat Sandstone was probably deposited 322 km from the strandline near an outer shelf margin. This interpretation is based on published strandline positions End_Page 783------------------------------ and on regional isopach maps of subsurface units within the Pierre Shale. Local thickening of shale marks the position of the shelf margin. Sandstone geometries may reflect ancient shelf features. Small-scale facies over 305 m may represent large sand waves such as are observed on modern shelves. The elongate northwest-trending lenses are similar in size and geometry to modern marine sand ridges, and the large area of sandstone may have been the site of close-spaced sand ridges. End_of_Article - Last_Page 784------------

SANDSTONE RESERVOIR GEOMETRY OF NON-MARINE SEDIMENTS IN THE TOOLACHEE GAS FIELD

The concept of Genetic Increments of Strata (GIS) has been applied to correlations of the non-marine rocks of the Early Permian Patchawarra Formation of the Cooper Basin. Boundaries of GIS in the non-marine rocks are related to a dynamic model of non-marine deposition in which discrete sandstone bodies result from channel activity.In the 9 wells in the Toolachee Gas Field area of about 150 sq. miles, log correlations based on these principles determined eight major sandstone bodies, six of which hold gas reserves. The sandstone bodies are elongate and sinuous. They have cross-sectional dimensions of about 5 miles wide by up to 60 ft thick. Faulting and differential compaction have influenced the locations of the axes of the channel sandstone bodies.The value of mapping the geometry of the channel sandstones in the Cooper Basin lies in establishing a possible trapping mechanism which is independent of structural closure and which requires only a structural dip nonperpendicular to the channel sandstone direction; and providing a geologic basis for gas reserve estimates, the positioning of future appraisal and development wells and the prediction of field extensions and nearby new fields.An estimate of the proven-probable gas in place in the Toolachee Gas Field (560 BCF) based on the channel sandstone mapping is comparable with estimates based on lumping all pay intervals together in each well and drawing geometric pay isoliths. Estimates of possible reserves are increased by the mapping because of the introduction of the trapping mechanism of sandstone margins. The Toolachee Field has the potential to be perhaps doubled in size.

Modeling of Noncontinuous Fort Union and Mesaverde Sandstone Reservoirs, Piceance Basin, Northwestern Colorado

Abstract A recent Federal Power Commission study indicated up to 600 trillion ft of natural gas in place in the Rocky Mountains in low-permeability place in the Rocky Mountains in low-permeability Cretaceous and Tertiary nonmarine sandstones. This type of reservoir rock bas been studied in the surface and subsurface in the Piceance Basin area of northwestern Colorado. The sandstone geometry and orientation are characterized in this paper. A "random intersection" technique is developed that uses the geological information to generate a spectrum of reservoir models that may be used to simulate the performance of conventional as well as hydraulically and nuclearly fractured wells. Example reservoir models for fractured wells are compared with reservoir models for nonfractured wells. In general, point-bar sandstones can be simulated by radial models and channel-fill sandstones by linear models. In a sequence of channel-fill sandstones with Piceance Basin geometry, an average well will be Piceance Basin geometry, an average well will be connected to about 18 percent of the in-place reservoir volume in a 320-acre area. Connected reservoir volumes of greater than 70 percent in a 320-acre area are calculated for fractured wells with fracture wing dimensions of 2,000 ft, with actual values depending on fracture extent and pervasiveness. The percent of connected reservoir pervasiveness. The percent of connected reservoir volume decreases as well spacing increases. Introduction Selecting an appropriate model for reservoir simulation can be a difficult task, especially if a minimum amount of subsurface data are available. In many areas, the reservoir rock outcrops within a reasonable distance of the field. Thus, the meager subsurface data can be supplemented by outcrop studies. This paper briefly summarizes the results of outcrop studies on the Mesaverde and Fort Union formations in northwestern Colorado and presents an evaluation of some reservoir models generated by using the outcrop information. This study was an attempt to use all available information sources to supplement the usual subsurface data. It is recommended that data from studies of rock types and geometries be used to help develop that best reservoir model possible; otherwise, important information is being ignored. SUMMARY OF GEOLOGY GEOLOGICAL SETTING The Piceance Basin is located in northwestern Colorado. The basin is a large structural downwarp with a sedimentary sequence more than 20,000 ft thick. The principal gas-bearing units are a series of fluvial Tertiary and Cretaceous sandstone lenses in the Fort Union and Mesaverde formations. A schematic section of the horizons encountered in the Project Rio Blanco area is presented in Fig. 1. A more comprehensive geological description is presented in Appendix A. presented in Appendix A. SUMMARY OF OUTCROP STUDY The Fort Union-Mesaverde sandstone bodies studied in outcrops along the periphery of the northern Piceance Basin appear to be predominately fluvial channel-fill deposits with some point-bar sandstones. The point-bar sandstones occur in the lower Fort Union section. The most commonly observed thickness was between 20 and 30 ft (manly channel-fill sandstones) and the log mean length/thickness ratio (L/h) was 35 for all of the observed sandstones lenses, with a minimum of about 19/1 and a maximum of about 140/1. Length/width (L/W) ratios (shape of body in plan view) average 2-4/1 for the Fort Union point-bar sandstones) and greater than 10/1 for the Mesaverde channel-fill sandstones (Appendix B). Average length/width/thickness (L/W/h) ratios are the following. Sandstone Formation Type L/W/h Fort Union Point-bar 190/90/1(Typical Case) - (7,600/3,200/40 ft) Mesaverde Channel-fill 140/14/1(Typical Case) − (3,500/350/25 ft) SPEJ P. 175

Why Explore the Northeast Margins of Los Angeles Basin?: ABSTRACT

Significant oil finds recently have been made in the northeasternmost Los Angeles basin. Exploration in the area has lagged because of supposed structural complexity and limited stratigraphic concepts. The development of stratigraphic concepts since the early 1950s now allows us to reinterpret and refine depositional patterns and resolve some of the structural complexity. Unlike other parts of the Los Angeles basin, land is still available in many areas and lease costs are reasonable, hence, a review of older records and recomputation of older geophysical work in addition to application of new and improved field and stratigraphic theory can lead to new oil finds. This is especially true along the basin edge with emphasis on source and distribution of sands. Exploration is best done before urbanization and attendant increased costs of operation. The new West Mahala pool can be used as a case history. The pool was discovered by M. J. Castro as a stratigraphic trap in late Miocene, Puente Formation sediments. The producing measures are in fan and canyon turbidite deposits in upper to middle bathyal sediments (800-3,000-ft water depth). There are two producing zones--the Willis and Langstaff zones. The sandstone geometries suggest fan deposition for the Willis, and channel or canyon facies for the Langstaff. Recovery factors, gas drive, and decline rates are typical of sands given this interpretation. Porosity and permeability data support these contentions. Reworked and shallow-water foraminifers are considerably End_Page 433------------------------------ more abundant in the displaced shallow-water sands. The probability of finding other fields which are somewhat analogous to the West Mahala pool are good. Geologic models used in exploration should include deep-water turbidite fan-channel complexes which may be distributed along the northeast side of the Chino, Puente, and San Jose Hills. End_of_Article - Last_Page 434------------

Patterns of Flysch Deposition of Lower Stanley Group (Mississippian), Ouachita Mountains, Oklahoma and Arkansas: ABSTRACT

A southern proximal and a northern distal flysch facies are recognized in lower Stanley strata over an area of 5,000 sq mi in the southern and central Ouachita Mountains. Four distinctive tuffs (25-120 ft thick) interbedded with marine graywackes and shales serve as key units for detailed correlation of 8 sections 500-1,500 ft thick. Sandstone geometry, lithology, sedimentary structures, and ratio of sandstone to shale in the proximal and distal facies are similar to modern deep sea fans and associated basin sediments off the southern California coast. Individual sandstones appear to be discontinuous finger- to fan-shaped bodies on isopach and paleocurrent maps. A gradational contact (10-100 ft) between the Arkansas Novaculite and the overlying lower Stanley strata over most of the Ouachitas records a gradual change from predominantly biological/chemical precipitation to clastic sedimentation. A local high, or highs, in the Ouachita trough is indicated by (1) novaculite conglomerate lenses, (2) an angular unconformity, and (3) thinning of the tuffs and strata between the tuffs. The lower 500 ft of the Stanley Group is predominantly a distal flysch facies of shales and thin (6-in.) siltstones over much of the Ouachitas. The distal facies was superseded by a prograding wedge of proximal flysch facies in the southern Ouachitas. The proximal facies changes laterally to a distal flysch facies in the central Ouachitas. The source area may have been a northeastern extension of the buried Luling overthrust front of Texas. End_of_Article - Last_Page 642------------

Quantitative Basin Analysis of Permo-Carboniferous Dunkard Group in Ohio, Pennsylvania, and West Virginia: ABSTRACT

It long has been known that the depositional strikes of some facies variables in ancient fluvial regimes are generally perpendicular to the inferred paleoslope. We propose that this is an effective criterion for selecting facies components whose regional distributions were primarily slope induced. A statistical model based on the postulated geometric relation between the paleocurrent pattern and the regional facies trends provides a means of identifying the trend components that were controlled by the depositional slope. On the basis of 134 measured sections in the Permo-Carboniferous Dunkard Group, paleoslope response components of 5 facies variables were selected using this model. Examination of these trends in conjunction with crossbed readings made at 389 localities reveals (1) a high concentration of clastics on the southeast, consisting primarily of thick belt sandstones (subgraywackes) and red mudstones, (2) a northern drainage outlet characterized by abundant freshwater limestone, coal, sheet sandstone, and gray-green shales, and (3) a second drainage basin to the west with sheet sandstones, red mudstones, and few limestones or coals. Analysis of the slope-induced facies trends indicates that sandstone geometry and distribution were controlled by the configuration of the paleoslope whereas the formation of limestone, coal, red mudstone, and nonred shale depended primarily on the relative positions of the groundwater table and the depositional surface. The Dunkard Group was deposited on a northward to westward sloping alluvial plain from which distributaries emptied into seas on the northeast and southwest of the present Dunkard basin. End_of_Article - Last_Page 349------------

Geometry of Fluvial and Deltaic Sandstones (Pennsylvanian and Permian), North-Central Texas: ABSTRACT

Upper Pennsylvanian and Lower Permian rocks of the eastern shelf in north-central Texas are composed of 10-15 repetitive sequences including open shelf, deltaic, fluvial, and interdeltaic depositional systems. Sediments derived from the Ouachita Mountains and associated piedmont were transported westward across a narrow coastal plain. Fluvial and deltaic sandstone facies define a southwest paleoslope of about 5 mi. Sandstones are delta-front, distributary-mouth-bar, distributary- and fluvial-channel, and destructional-bar facies. Distributary patterns represent distal deposition in the upslope area. Belt sandstones, typified by unusually thick fluvial channels, prograded far downslope. Composite patterns include distributary and belt sandstones representing complex progradational history. Rocks display ½° northwest regional dip; negative structure residuals outline a broad area within which 70% of the deltaic facies were deposited. Elongate sandstones generally are arranged parallel with paleoslope in vertically offset patterns controlled by differential compaction of fluvial and deltaic sands and interdistributary muds. Multistory sandstone bodies were deposited along narrow, structurally unstable belts which were periodically overloaded and later reoccupied by prograding deltas. Initial Cisco deltas followed a paleosurface grain controlled by underlying bank limestones; this paleoslope orientation was maintained during deposition of 1,200 ft of Cisco strata. Each fluvial-deltaic system inherited its geometry from previous systems and, in turn, provided control for the next deltaic episode. Stratigraphic and structural mapping utilizing mud decompaction techniques confirm the roles played by compaction and stru ture in controlling the geometry of sandstone bodies. End_of_Article - Last_Page 2033------------

Diagenetic Aspects of Lower Morrowan, Pennsylvanian, Sandstones, Northwestern Oklahoma

Diagenesis has profoundly altered the reservoir capacity of some lower Morrowan sandstones in the Anadarko basin. Definitions of sandstone geometry, depositional environment, etc., comprise only part of the information necessary to explore intelligently for hydrocarbons in these rocks. Most of the lower Morrow sandstones were deposited in a broadly transgressive system. Two basic types of sandstone are recognized: (1) Type A is a very nearshore, clean, well sorted, non-glauconitic, non-calcareous sandstone deposited in a high energy environment; (2) Type B is a seaward facies of Type A, deposited under lower energy conditions and is normally poorly sorted, glauconitic, calcareous, and here and there shaly. Petrographic analyses indicate Type A sandstones have either (1) extreme pressure solution and no permeability, or (2) moderate to minor pressure solution with secondary quartz overgrowth cement. These rocks are generally permeable when medium- to coarse-grained and impermeable if fine-grained. Upper and lower edges of some sand bodies are tightly cemented with CaCO3 possibly through ionic impedance at the sand-shale boundary. Type B sandstones have been diagenetically altered by minor secondary quartz overgrowth and pressure solution, extensive carbonate cementation, and some authigenic clay. Commercial permeability is associated with secondary removal of carbonate cements. Such reservoirs have random shapes and are difficult to predict or evaluate. A qualitative petrographic rock fabric classification based on relative degree of pressure solution, type of grain outlines and contacts, amount and type of cement and porosity is useful in mapping their geographic distributions. Integration of this type data into normal subsurface exploration methods is helpful for the understanding of the lower Morrow in the area studied.

Visual Examinations of Fluid Behavior in Porous Media - Part I

Abstract An exploratory study was made to examine the possibilities of a visual approach in investigations into microscopic mechanisms of fluid behavior in porous media. Appropriate apparatus and techniques were developed so that microscopic phenomena could he recorded on color movie film as well as be observed visually. The observation flow cells in which the fluid behavior studies were made were essentially single-layered matrices of spheres between plates, sometimes all-glass, sometimes all-Lucite and sometimes a combination of the two. The fluids were limited to water and a filtered crude oil. Two flow regimes were observed during the flow of the immiscible liquids: channel flow and slug flow. In the former, transport was effected through stable networks of interconnecting channels; and in the latter, part of the movement took place in the form of slugs. Under certain conditions, flood-front patterns were found to be different depending upon which liquids were the displacing and displaced phases and not depending upon whether the matrix was water-wet glass or oil-wet Lucite. Residual formations of oil and water were observed and are described. Some of the ramifications and significance of the observed phenomena are discussed. Introduction In recent years considerations of microscopic mechanisms of fluid flow in porous media have taken on greater significance. Much needs to be learned before the fundamentals of petroleum technology are completely established. For example, many unanswered questions exist in connection with relative permeability, displacement phenomena, residual fluid formations, flow structure, etc.; and further analytical mathematical formulations are seriously indicated. It is hoped that systematic investigations into the microscopic mechanisms connected with the behavior of fluids in porous media will shed some light on some of the problems extant. Until recently microscopic mechanisms have been considered almost exclusively as speculative hypotheses. Within the past few years, however, the problem has been submitted to a limited number of experimental investigations. Nuss and Whiting made some studies on the pore-space geometry of sandstones and limestones by impregnating cores with an inert plastic and leaching the solid matrices to leave behind plastic models of the pore spaces. Schaefer traced pore spaces microscopically through lengths of limestone cores by cutting away thin sections from the exposed faces normal to the line of view.