Interstitial Clay Research Articles

Geologic Controls on the Production Characteristics of Cyclical, Mixed Carbonate-Clastic Gas Reservoirs, Lower Permian Chase Group. Guymon-Hugoton Field, Oklahoma: ABSTRACT

The Lower Permian Chase Group, Guymon-Hugoton field, Oklahoma, is composed of interlayered carbonates, siliciclastics, and evaporites deposited in cyclical, shallowing-upward sequences on a gently dipping, low-relief shelf. Each cycle forms a reservoir layer comprised of laterally continuous, successively shallower water marine carbonates and siliciclastics capped and separated by shaly red beds and paleosols. Reservoir studies indicate that individual reservoir layers have contrasting permeabilities and volumes, are not in pressure communication and exhibit different depletion characteristics. No virgin pressures have been revealed by recent drilling, indicating that no new gas has been discovered and that the current well-spacing pattern has been efficiently draining the field. Siltstones and sandstones consist of framework quartz, feldspar, mica, and rock fragments and interstitial clay, carbonate, and anhydrite; porosity is primarily intergranular. Within cycles, limy or dolomitic skeletal, pelletal, and oolitic subtidal grainstones to wackestones grade upward into intertidal to supratidal wackestones and mudstones. Intergranular and crystal- or grain-moldic pore types and a well-developed, laterally continuous, intercrystalline, pore system, produced by dolomitization and independent of depositional texture and other pore types, provide fair to excellent porosity and permeability within individual reservoir layers. Lateral continuity of the intercrystalline pore network and individual reservoir layers promotes good fieldmore » drainage. Shaly layers are composed of shaly mudstones and argillaceous carbonates that exhibit low permeabilities and high threshold entry pressures. Primary components include illitic, chloritic, and smectitic clays, authigenic carbonate and anhydrite, and detrital quartz, feldspar, and micaceous silt.« less

Estimation of the Migration Parameters for the Boom Clay Formation by Percolation Experiments on Undisturbed Clay Cores

ABSTRACTThe safety assessment of the repository for high level radioactive waste in the Boom clay formation requires reliable data for the migration parameters. The experimental set-up and the interpretation method is briefly described for percolation experiments on undisturbed clay cores drilled from the formation and results are reported. The undisturbed clay cores are drilled perpendicular and parallel to the stratification of the formation to study the isotropy of the formation. To represent the real situation as close as possible, in-situ interstitial clay pore water is used as percolating liquid.Parameter values determined in the percolation experiments are presented for bromine, iodine and tritiated water. Darcy velocity and effective stress are used as variables. Anisotropy of the formation is demonstrated for the hydraulic conductivity, but is found to be trivial for the dispersion parameters. A general relation between the apparent dispersion constant, the diffusion accessible porosity and the Darcy velocity is also given.

Mechanically Infiltrated Clays: Recognition and Influence in Fluvial Reservoirs of Reconcavo Basin, Brazil: ABSTRACT

Fluvial sandstones and conglomerates of the Sergi Formation (Jurassic) are the main reservoirs of the Reconcavo basin in northeastern Brazil. These reservoirs contain significant amounts of interstitial detrital clays resulting from early diagenetic mechanical infiltration. The infiltration developed under arid/semiarid conditions, where the lowered water table allowed muddy waters of episodic runoff to infiltrate through the coarse alluvium. The main clay concentrations occurred in the upper phreatic zone and in proximity to sources of influent seepage. It is difficult to identify infiltrated clays in ancient sedimentary rocks due to a lack of well-established petrographic criteria. In this work, a series of petrographic criteria is proposed to recognize these clays in clastic reservoirs. These criteria include the anisophachous coatings of tangentially accreted lamellae and the geometric patterns developed due to shrinkage. The infiltrated clays are among the main controls of reservoir properties, and the horizons of maximum clay concentration are the main internal barriers in most Sergi reservoirs. In general, infiltrated clays damage reservoir quality by creating macroheterogeneities and microheterogeneities, by decreasing recovery efficiency and permeability, and by increasing water saturation. Also, they can cause formation damage either by their swelling properties or through the migration of loose particles left bymore » shrinkage. As demonstrated in the Sergi Formation, infiltrated clays must be adequately identified for the definition of proper procedures for drilling, completion, reservoir development, and EOR programs.« less

Diagenetic alteration of detrital biotite in Proterozoic sedimentary rocks from Sweden

The alteration of detrital biotites has been studied in two clastic Proterozoic sedimentary sequences from southern and central Sweden, namely the Visingsö Group and the Dala Sandstone, respectively. The results showed that the biotites are altered through replacement by clay minerals (illite, chlorite and less commonly kaolinite). Biotite may either be replaced pseudomorphically (one biotite crystal by one clay mineral crystal) or by fine-crystalline clay minerals which merge into the interstitial clay matrix. In reddish rocks, biotite may be associated with pigmentary hematite and in greenish rocks with pyrite. The variation in the two textural habits of biotite alteration, i.e., pseudomorphic or fine crystalline, is related to physico-chemical properties of pore solution and nature of biotite particles.

古期深層風化殻の形成と後期第三紀以降の地形化作用 ＩＩ 風化殻の形成と地形

Wide and flat planes found on top of mountains are often related to deep weathering crusts of the Miocene and Pliocene Ages. Because surfaces of the crusts are porous and mechanically weak, they are easy to suffer from aeolian and frost actions, and flattened during glacial ages.Process of weathering is significant to the morphogeny and therefore to the recent morphology in Japan. In this respect the mechanism of deep weathering is discussed. In aquifer or waterholding parts of the crust, rocks as well as water change chemical properties in course of weathering reactions from surface to bottom. Near the surface rocks are leached under acidic conditions with CO2 and water. Beside silica, alkali and alkali-earth are romoved in ground water to react and replace mother rocks beneath. Further removed materials are deposited as interstitial clay or opal under nutral or slightly alkaline conditions. Therefore by removal of weathering products the reaction continues in the same direction to change chemical conditions, and form an almost closed system between rocks and ground water in the aquifer. The weathering crust includes a whole pack of reacted, replaced and deposited materials in the aquifer.Taking granitic rocks as typical components of the earth's crust, layered structure of weathering crusts are described. They are made up of 3 layers of horizontal zones as follows : In the top of the granitic crust completely leached rocks are found as saprolites, in which original textures of rocks are presurved, although most minerals except quartz are converted into kaolinite, halloysite or gibbsite. Density of original rock (2.68g/cm3 in a fresh granodiorite) is reduced to 1.0g/cm3 in dry condition. Here almost 60% of materials are leached. The upper part of the layer is red coloured by ferric oxides, while lower part is white by halloysites. Because rocks are porous, lightened and weakened, the upper most part of the crust is often removed by wind and the crust is truncated by wide aeolian surfaces.In the second layer, rocks are moderately weathered manganese and ferrous hydroxides are deposited beside removed clay minerals, tuch as halloysite and vermiculite. Quartz and most feldspars are not decomposed, but micas are changed ingo vermiculite. The layer is 1.8-2.0g/cm3 in density. It is represented by the montmorillonite zone in another kind of weathering crust, containing dacite, dacite tuff and another volcanics.In the third layer, rocks are not changed chemically nor minerallogicaly, but they are fractured or fragmented by open clacks along grain boundaries or cleavages. Density of the rock is reduced to 2.4-2.0g/cm3 in this layer by leaching reaction of percolating water.Change in density by weathering is closely related to the geomorphology especially to the inclination of slopes along valleys.

Reservoir Quality of Lower Jurassic Muddy Sandstone Reservoirs, Western Sverdrup Basin, Arctic Canada: An SEM Study: ABSTRACT

Clayey sandstones of the Lower Jurassic King Christian Formation, deposited in progradational sequences of shelf and deltaic environments, are the principal gas reservoirs in the deeper areas (about 2000 m and greater burial depth) of the western Sverdrup basin. The sandstones are dominantly fine-grained and argillaceous. Clay content ranges from 8% to greater than 30%. A scanning electron microscope (SEM) study of these compacted and tight sandstones revealed abundant leached porosity and microporosity in the interstitial detrital clay matrix. Clay diagenesis revealed by SEM includes dissolution of illitic clay matrix and carbonaceous clays, and growth of kaolinite and illite. Clay diagenesis occurred during intermediate to deep burial. The intensity of clay mineral transformation correlates well with organic metamorphic facies. Burial leaching of the clay matrix can be attributed to an increase of P/sub CO/sub 2// and a buildup of H/sup +/ in the pore fluids. Acidic fluids possibly migrated into the reservoir from the underlying and overlying source shales associated with increasing maturation temperatures. Hydrocarbon production from the deeper reservoirs in the western Sverdrup basin will be primarily from secondary leached porosity in the clay matrix, where late-stage cementation was arrested by earlier hydrocarbon migration. Full reservoir quality and potential more » of these clayey sandstones can be evaluated only by detailed SEM examination of core materials and well cuttings. « less

Stratigraphy and Petroleum Potential of Berea Sandstone in Larkin and Williams Fields, Midland and Bay Counties, Michigan: ABSTRACT

The Berea is an Early Mississippian deltaic sandstone confined to the eastern side of the Michigan basin. The Berea Sandstone consists of three members: upper, middle, and lower. Only the upper and middle members are present in the Larkin and Williams area. The middle member is the main reservoir, and scanning electron microscope studies indicate that the sand has primary, interparticle porosity with some secondary leaching of interstitial clays and feldspathic grains. Over the past 5 years, wells have been drilled 2500 ft into the Berea along a structure between Midland and Bay Counties. The structure is a northwest-southeast-trending anticline that plunges northwest into the basin. A review of the wells drilled along this anticline reveals a progression of structural-stratigraphic traps within the middle Berea member. At the southeast end of each reservoir (the updip end), a stratigraphic pinchout cuts across the middle Berea member creating a barrier to oil migrating updip along the northwest-southeast structural trend. These pinch-outs are narrow with a north-northeast orientation and are considered to be abandoned, mud-filled channels cutting across an apron sheet sand, which is interpreted to be a beach-strand-plain complex. Because the middle Berea member has excellent porosity and permeability, many wells inmore » the field have flowed oil with initial production ranging between 75 and 350 BOPD. The original oil in place is estimated to be more than 23 million bbl of oil; only 1.4 million bbl of oil has been produced.« less

The application of lithogeochemistry in the search for unconformity-type uranium deposits, Northern Saskatchewan, Canada

Lithogeochemical-mineralogical haloes around unconformity-type uranium deposits in northern Saskatchewan can expand the size of drill targets up to fifteen times. The deposits are located at or near the unconformity between Aphebian metamorphosed basement rocks in close proximity to Archean granitoids and overlying unmetamorphosed sandstones of the Helikian Athabasca Group. Deposits studied include Key Lake (Deilmann), Midwest Lake and Eagle Point. Unconformity-type deposits are associated with broad alteration haloes in the overlying sandstones and more restricted haloes in the basement rocks. The haloes in the sandstone are localized around steeply dipping fault structures and are characterized by zones of intense leaching of specular hematite and detrital heavy mineral layers and by changes in chemistry related to clay mineral alteration and tourmalinization. Clay mineral alteration haloes are common in the sandstone and basement host rocks. Interstitial clays consist mainly of kaolinite and illite with lesser amounts of chlorite. The ratio K 2O/AI 2O 3 proved useful in delineating illite-kaolinite patterns in the sandstone and in the uppermost portions of the paleoweathering profile in basement rocks. The Midwest deposit is characterized by a broad bell-shaped zone (500 m across strike) of high K 2O/AI 2O 3 ratios (>0.18) in which illite is the dominant clay mineral. The sandstone above the Deilmann deposit, on the other hand, is characterized by silicification and kaolinitization with low K 2O/AI 2O 3 ratios (<0.04). This kaolinite cap overprints a preexisting illite zone. Anomalously high boron values are characteristic of the three deposits considered in this study. Boron anomalies are similar in extent to the anomalous clay mineral alteration haloes. Altered sandstones commonly contain aggregates of radiating magnesium-rich dravite needles within the clay matrix. The interpretation of boron patterns is problema tical however, mainly because of the detrital tourmaline component in sandstones and metamorphic tourmalines present in the Aphebian metasediments. Trace elements such as U, Ni, As and Co are generally of limited use in expanding targets in sandstone because their haloes are restricted to a few tens of metres horizon-anomalies along the steeply dipping zones of mineralization related to fault structures. Uranium (>3 ppm) does form an anomaly more than 200 metres laterally across the Midwest deposit. At the Deilmano deposit anomalous uranium dispersion is restricted to within a few metres of high grade ore. In the basement rocks, the various layers of the paleoweathering profile are geochemically overprinted up to 250 m from mineralization. Bleaching related to illitization and chloritization is associated with enrichment in K 2O, MgO, B, S, U, As, Ni and P 2O 3. The ratio Fe 2O 3/MgO is useful in delineating chloritization in the upper portion of the paleo weathering profile. Deposits with large root extensions in the Aphebian metasediments such as Eagle Point, have intense dravite-chlorite-illite alteration zones which are restricted to within a few metres of mineralization across strike. ‘Quartzite” units are alteration related. The complexity of the basement lithology inhibits the use of individual elements as alteration guides other than in the intensely altered zone. The application of multivariant techniques, element ratios and clay mineralogical work prove useful in identifying the mineralogical changes at Eagle Point.

Sedimentology and Development of Shallow Heavy Oil Deposit, Eastburn Field, Missouri: ABSTRACT

Eastburn field, Vernon County, Missouri, produces heavy, 21° API, crude oil at a depth of 110 ft (33 m) from a thin, 20 to 30 ft (6 to 9 m), sandstone stratigraphic trap in the Cherokee Group of Middle Pennsylvanian age. Sedimentary structures, grain-size trends, and geometry of the sandstone and the nature of associated sediments indicate the fluvial-deltaic origin of the reservoir. Development drilling at very close spacing, 200 ft (60 m) between wells, provided information from which a sedimentologic model of the Eastburn field reservoir could be developed early in project life. From this model, strategies were proposed that guided further drilling and completion of wells, extension of the field, and placement of production facilities. Development drilling guided by the sedimentologic model resulted in tripling the known volume of the heavy oil resource, with a minimum number of dry development wells being drilled. The reservoir sandstone is composed mostly of medium to very-fine sand-sized quartz, rock fragments, and mica, with abundant interstitial detrital silt and clay. Authigenic kaolinite clay, and calcite and siderite cements reduce reservoir quality and contribute to problems in production, such as low injectivity of steam and exhaust gases in the thermal recovery process. Identification of the permeability reducing minerals aided in design of well-stimulation treatments and contributed to increased productivity. In a few places, where contouring of the sandstone thickness was doubtful, production performance of individual wells provided additional data to guide the geologic interpretation. This synergistic approach helped to minimize the cost and maximize the efficiency of the field development. End_of_Article - Last_Page 566------------

Geologic Analysis for Enhanced Oil Recovery, Madison Block, Greenwood County, Kansas: ABSTRACT

Five oriented cores from the Cities Service Co. enhanced oil-recovery project, Madison Block (Unit B) of the Seeley-Wickfield, were analyzed. Primary production, air, and water drives in the Middle Pennsylvanian Bartlesville Sandstone (Cherokee Group) have produced 12.5 million bbl of oil with 18.6 million bbl remaining. Six depositional facies are recognized in the cores. The End_Page 942------------------------------ facies are, in ascending order, a prodelta shale and siltstone facies, a distributary channel sandstone facies, an overbank shale and siltstone facies, an interdistributary bay and splay channel facies, an estuarine sandstone, shale, and siltstone facies, and a lagoonal sandstone and siltstone facies. This genetic vertical sequence package, typical of fluvial-deltaic sediments, is typified by an upward change in the scale of sedimentary structures, an increase in radioactivity of the gamma ray log, a decrease in grain size, a decrease in permeability, and a subsequent increase in the amount of interstitial clay matrix. Permeability is primarily controlled by packing, sorting, the presence of ductile rock fragments, and the amount of clay matrix. Permeability of the distributary channel sandstone facies, the primary reservoir, decreases from 60 to 100 md in trough cross-bedded sandstones to 20 to 60 md in rippled sandstones and siltstones. Low permeability values (0 to 20 md) are characteristic of facies containing siltstone and shale. The distributary channel sandstone facies (28 to 62 ft or 8 to 19 m thick) is continuous across the pilot project area and varies in thickness in a predictable manner. Dip directions of trough cross-beds observed in four oriented cores suggest that the distributary channel flowed to the west-southwest across the project area. The overbank shale and siltstone facies and the interdistributary bay and splay channel facies are not continuous across the project area and are interpreted to have been deposited in the topographically low area adjacent to the distributary channel. End_of_Article - Last_Page 943------------

Wilmington Field, California, Polymer Flood A Case History

The failure of the Ranger Zone Fault Block V polymer flood in the Wilmington field is discussed. The apparent poor results indicate the need for better reservoir information and improved knowledge of polymers and their behavior underfield and reservoir conditions. Introduction The ever-increasing world demand for crude oil, combined with dwindling reserves and the need to improve efficiencies of waterflood operations, resulted in laboratory studies and field tests of recovery processes that would improve the mobility ratio. It has long been recognized that improved mobility ratios should bring about increased displacement efficiencies, thereby resulting in greater oil recovery. When added to injection water, the Dow Pusher chemicals, which are high molecular-weight, water-soluble polymers, decrease the water mobility in porous media polymers, decrease the water mobility in porous media many times more than would be expected from the increased viscosity of the injected brine. In early 1967 Dow approached the unit operator of the Fault Block V Unit, Wilmington oil field, with a proposal to add polymer to the existing waterflood. A portion of the unitized area of the Ranger Zone was designed for a Pusher flood with injection beginning in July 1969. Pusher flood with injection beginning in July 1969. Initial polymer concentration was 150 ppm, which was increased to the designed concentration of 250 ppm later in the life of the flood. The Pusher flood area, the pattern of injection wells, and the producers included in this study are shown in Fig. 1. Geology and Reservoir Characteristics The Wilmington oil field, as shown in Fig. 2, is located in Long Beach, Calif.; about 30 miles south of Los Angeles. Development of the seven oil-bearing zones began in 1937. Full-scale waterflooding on the south flank of the Ranger Zone was started in 1958, in the later stages of primary depletion. The field is cut by a system of north-south faults that divides the producing zones into a series of "fault block" reservoirs. The Ranger Zone reservoir in Fault Block V is bounded by the Harbor Entrance fault on the west and the Golden Avenue-Daisy Avenue faults on the east, as shown in Fig. 3. This pool is unitized between the Harbor Entrance fault and the Los Angeles County flood control channel. The eastern third of the pool is operated under a cooperative agreement with Standard Oil Co. of California. Pay zones are found from about 2.200 to more than 7,500 ft. The vertical pay intervals are divided into seven zones, more or less depending on edge-water profiles. The Ranger zone, found at depths ranging from about 2,500 to 4,000 ft. has the greatest areal extent and spans the Pliocene-Miocene contact. The Ranger Zone sands are arkosic (composed of feldspars. quartz. micas, heavy minerals, and some interstitial clays). They are generally loose to friable and range from thin interbeds to beds that are 10 to 5O ft thick. The sand units are blanket-type insofar as the over-all zone is concerned, although individual members are extremely lenticular within the zone. Because of their unconsolidated nature, core porosities (30 to 40 percent) measured at surface pressure are high. Recent studies indicate considerably lower reservoir porosities and higher connate water saturation than were porosities and higher connate water saturation than were measured at the initiation of the Ranger Zone flood. Permeabilities are generally high and run into the darcies. Permeabilities are generally high and run into the darcies. JPT P. 1473

Warm Air Coking Sand Consolidation Field Results In Viscous Oil Sands

Abstract Warm air coking is a completion technique that has been used to prevent the production of sand into wells producing from unconsolidated sand formations. It is accomplished by injection of heated air into the formation around a producing wellbore until the crude oil becomes oxidized into an insoluble coke or resin which binds the sand grains together. In addition to stabilizing the loose sand, the heated air stimulates oil production. Results of several field tests where loose sand reservoirs saturated with viscous crude oils have been consolidated in the producing wellbore are presented and discussed, as are illustrations of the stimulated producing rates and descriptions of the equipment used in performing the sand consolidation. Based on results of the field tests, the details of a typical completion and the potential of the technique as a completion tool are analyzed. Introduction Sand control has been acknowledged as a producing problem in unconsolidated sand reservoirs for many years. As the viscosity of the produced crude increases, the sand control problem becomes more complex. In the early days of the development of shallow, unconsolidated sand reservoirs containing viscous crude oils, many of the oil operators contended that the sand should be produced with the oil. In early wells, provisions were made to bail both sand and oil from open-hole completions. Later, slotted liners with 0.18 to 0.20-in. openings were used which supported the wellbore but permitted the oil to carry sand into the well. Today, slotted liners, screens and gravel packs are the primary completion tools for wells producing viscous oil from unconsolidated sands. The only major change in California in recent years has been a general reduction of the slot size to 0.100 in. or less in an attempt to exclude the loose sand. Even though each of these mechanical methods has achieved some degree of success, each has inherent disadvantages. None of the mechanical devices affords permanent protection from recurring sand production. With mechanical devices in the wellbore, multiple completions are difficult. There are problem cases where mechanical devices have been completely unsatisfactory. The degree of selectivity is limited and interbedded water-bearing formations must be contended with in some producing areas. Several sand consolidation methods are presented in the literature. The diversity of approach emphasizes the fact that intensive research efforts have been directed toward the development of an effective sand control completion. Incentive for this research has been provided by several factors: There is a need to maintain high productivity while controlling sand production. This is especially true in low gravity oil reservoirs that have not been developed because of sanding problems. A reduction of permeability can occur in some unconsolidated sands when they are permitted to move. If the unconsolidated sands contain interstitial clay, the reduction of permeability can be substantial since the clay particles become redistributed during movement. In these cases it would be desirable to consolidate the sand in the initial completion. Well and workover costs caused by sand influx could be eliminated. The recent development of thermal recovery processes with their greatly accelerated rates of production emphasized the immediate need for permanent sand control (as well as some degree of selectivity) before many of the unconsolidated reservoirs can be successfully depleted by secondary methods. Thermal recovery processes have demonstrated their greatest application in viscous oil reservoirs which in turn present some of the most severe cases of sand control. This paper presents field test results of the warm air coking process. The potential of this method of sand consolidation in viscous oil sands has been demonstrated by stabilizing unconsolidated sand in several wells producing 12 and 14 degrees API gravity oil. In addition to consolidating the wellbores, the heat generated by the injected air has stimulated oil production for a limited period. JPT P. 35ˆ

LOG INTERPRETATION IN SANDSTONE RESERVOIRS

By comparison with carbonate rocks sandstones are texturally homogeneous; in consequence the interpretation from well logs of the fluid content and physical properties of sandstones is relatively simple. From an exploration standpoint one significant fact must be gleaned from the log: Will the formation of interest produce oil or gas? The precise porosity and thickness of the formation and its exact hydrocarbon saturation are, initially, secondary considerations. Some of the principal difficulties involved in determining interstitial water resistivity, porosity and formation resistivity are examined. It is confirmed that the so‐called “low zone” significantly decreases the resistivity of an oil‐bearing sand when this resistivity is found from an induction log. Theory and laboratory experiment confirm that diffusion and convective mixing of the filtrate and interstitial water do little to mitigate the problem. It is suggested that future correction charts for induction logs recognize this fact. New data bearing on the dirty sand problem show that if formations contain interstitial clay the interpretation procedure suggested by A. J. de Witte is substantially correct. It is pointed out that the real problem is to decide the manner in which the clay content of a typical dirty sand is disposed. Measurements on the effect of the porosity of sandstones on the difference between velocities through them when dry and fully water‐saturated disclose an interesting paradox: The velocity difference is a maximum when the porosity is a minimum. Significant differences in velocity between gas‐ and water‐saturated sandstones are not to be expected in the porosity range of practical significance.

An Evaluation of the Procedures Used in the Determination of the Grain Densities of Petroleum Reservoir Minerals

Published in Petroleum Transactions, AIME, Volume 210, 1957, pages 235–244. Abstract Several of the commonly used methods for determination of effective grain densities of minerals have been evaluated for accuracy and precision, and their applicability to various types of petroleum reservoir minerals tested. Consideration was given to the effect of consolidation, swelling clay, and wettability on these grain-density determinations. Procedures with helium displacement, a modified low-pressure Boyle's law porosimeter, and liquid displacement (water, n-decane, and n-octanol) were tested. The helium-displacement procedure was used primarily as an independent reference for which the effects of fluid-solid interaction, e.g., adsorption and wettability, were negligible. The procedures with the Boyle's law porosimeter and with liquid displacement are the methods in common use. Minerals investigated included calcite, West Texas limestone core samples, California sandstone core samples, and Wyoming bentonite. The number of samples tested, while not large, was adequate to permit application of statistical methods. Grain-density measurements on calcite (Iceland spar) provided a basis of comparison for the accuracy and precision of the procedures under investigation for a material with a high degree of chemical and physical homogeneity and for which fluid-solid interactions were at a minimum. Liquid-displacement procedures (water or n-decane) provided the greatest reliability and precision for measurement of the grain densities of the limestone tested. Gas-displacement procedures (helium or Boyle's law porosimeter) provided the greatest reliability and experimental convenience, if not the greatest precision, for the measurement of the grain densities of the swelling clay, Wyoming bentonite, and the shaly sandstones which contained appreciable amounts of swelling, interstitial clays. These experiments were designed to evaluate the applicability of the grain-density procedures in common use to some of the less tractable minerals-tight limestones, shaly sandstones, and swelling clays. The results should provide a useful basis for a selection of the method most suitable for application to the various petroleum reservoir minerals encountered and especially for use in the estimation of formation porosity.

Glauconitic Mica in the Morrison Formation in Colorado

AbstractGlauconitic mica occurs as interstitial clay in a bed of fine-grained sandstone, 15 feet thick, in the upper part of the Brushy Basin shale member of the Morrison formation of Late Jurassic age on Blue and Lone Tree Mesas near Uravan, Montrose County, Colorado. This glauconitic mica, similar to other material ordinarily called glauconite, is interesting because the Morrison formation is generally regarded as nonmarine in origin, whereas glauconite commonly forms in a marine environment.The identifying properties of the glauconitic mica are: strong 001 d spacing, 9.97A; very weak 002, 5.01A; strong 003, 3.34A; 060, 1.51A; green color, pleochroic; X and Z indices, approximately 1.578 and 1.600; SiO2 49 percent, Al2O3 18 percent, Fe2O3 13 percent, FeO 1.3 percent, MgO 2.8 percent, K2O 7.8 percent, TiO2 1.1 percent, ignition loss 6 percent, others approximately 1 percent.The glauconitic sandstone is underlain by variegated mudstones about 480 feet thick, which contain montmorillonite (with very sparse relicts of shards), illite, quartz, and also, in several layers, scanty analcime. The Burro Canyon formation of Early Cretaceous age overlies the glauconitic sandstone.This paper discusses alternative origins of the glauconitic mica possible within the framework of an appropriate chemical environment other than, and apart from, one typically marine.

Pennsylvanian Rocks of Eastern Interior Basin

Pennsylvanian rocks of the Eastern Interior basin underlie about 53,000 square miles in Illinois, Indiana, and western Kentucky, with small outliers in Missouri and Iowa, attaining maximum thickness of about 2,500 feet in southeastern Illinois. At the beginning of the Pennsylvanian there was a regional southwest slope furrowed by numerous subparallel valleys as deep as 200 feet. An eastward slope prevailed along the western border of the basin with smaller valleys. Subjacent strata range in age from the Middle Ordovician St. Peter sandstone to the Upper Mississippian Kinkaid limestone. Because of topographic unevenness and early Pennsylvanian tectonism, the early Pennsylvanian Caseyville and Tradewater units vary from zero to 1,200 feet. Movements along the LaSalle anticl ne and Duquoin monocline are reflected in an isopach map of this interval. In later Pennsylvanian Carbondale and McLeansboro time the intervals increase regularly toward the southeast, showing that the present southeast border of the basin is due to post-Pennsylvanian deformation. Structural relief on the No. 2 coal ranges from +700 to -913 feet. Similar systems of nomenclature are used in Illinois and Kentucky but different names are employed in Indiana. The significant features of 46 key beds are described. Clastic ratios average about 8 parts clastic to 1 non-clastic. Sand-shale ratios are extremely variable due to lenticular sandstones at more than 20 positions. Many sandstones occupy channels excavated into underlying strata; others seem to be off-shore barrier beach deposits. There are marine limestones at about 25 different positions, generally thickening toward the western border of the basin, but each has its individual pattern of distribution. Lower Pennsylvanian sandstones are highly quartzose and derived from older sediments; later sandstones are micaceous and feldspathic with much interstitial clay, evidently a first-cycle deposit from a metamorphic terrane. Coals are generally banded, and range in rank from high-volatile to medium-volatile bituminous. Refractory underclays ar found in the Lower Pennsylvanian in northern Illinois and in the area near St. Louis, Missouri. Cyclic sedimentation is very well displayed with at least 25 alternations of coal, marine limestone, shale, sandstone, and underclay. Early Pennsylvanian sediments came from the east and northeast but the source of the later micaceous sandstones is still uncertain. Most marine invasions came from the west, north of the Ozark uplift, but some in the early Pennsylvanian probably entered the basin from the east and south. The basin has produced about 5 billion tons of coal and 325 million barrels of Pennsylvanian oil. Other industries based on Pennsylvanian materials are refractories, common brick and tile, road metal, agricultural limestone, portland cement, rock asphalt, glass sand, foundry sand, and whetstone.

An Experimental Investigation of the S.P. and Resistivity Phenomena in Dirty Sands

Abstract The importance of the so-called "dirty sand" or "conductive solids" problem in electric log interpretation was first stressed in a paper presented in 1949. Since that time the problem has been generally recognized as a most serious one. Several research papers bearing on the theory of the effects of clay contaminants on reservoir rock resistivities have appeared. These papers, while contributing to the theory of the problem, have not offered any practical solution. In the present paper an experimental investigation has been made of the effects of ion-exchange materials on the electrical properties of natural and synthetic porous media. The method used to make synthetic dirty sands is entirely novel and has proved a valuable guide to a better understanding of the properties of dirty sands generally. The effects of ion-exchange materials on both the resistivity and self potential (S.P.) logs have been examined. From the data obtained it has been possible to formulate a simple, practical method whereby electrical logs of dirty sands can be qualitatively interpreted. The method is in all essentials identical to that presently in use for interpreting clean sands. New light has also been thrown on the significance of the term formation factor when it is applied to dirty sands. Introduction In 1949 a paper was presented which showed that the presence of so-called "conductive solids" introduced considerable complexities into the analysis of the resistivities of dirty sands, i.e., permeable formations containing clay. The reduction of the self potential (S.P.) resulting from the presence of interlaminated shale or interstitial clay in permeable formations has been discussed by Doll. Noteworthy papers which dilate further upon the effects of shale and clay on the resistivity of permeable formations are those of deWitte, Berg, Wyllie, and most recently, Winsauer and McCardell. The last authors have endeavored to elucidate the chemistry of the resistivity phenomena in dirty sands in terms of an adsorption hypothesis. Specifically, they attribute the electrolytic conductivity of shales and clays within a permeable formation to an ionic double-layer effect and, for this reason, regard the term "conductive solids" as a misleading one. Some consideration has been given to the effect of dirty sands on the S.P. by Wyllie and by McCardell, Winsauer and Williams.

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.

Evaluation Of Capillary Character In Petroleum Reservoir Rock

Abstract Improved apparatus, methods, and experimental techniques for determining thecapillary pressure-saturation relation are described in detail. In thisconnection a new multi-core procedure has been developed which simplifies theexperimental work in the study of relatively homogeneous reservoirs. The basictheory concerning the Leverett capillary pressure function has been extendedand has been given some practical application. Some discussion is presented toindicate the relationship of relative permeability to capillary pressure, andto provide a new description of capillary pressure phenomena by introducing theconcept of the psi function. Introduction For the purposes of this paper the capillary character of a porous mediumwill be defined to express the basic properties of the system, which produceobserved results of fluid behavior. These basic properties may be classified inthe following manner, according to their relationship to:The geometrical configuration of the interstitial spaces.This involves consideration of the packing of the particles, producing pointsof grain contact, and variations in pore size distribution. The packing itselfis often modified by the secondary processes of mineralization which introducesfactors of cementation, and of solution action which causes alteration of porestructure.The physical and chemical nature of the interstitial surfaces.This involves consideration of the presence of interstitial clay coatings, theexistence of non-uniform wetting surfaces; or, more generally, a considerationof the tendency towards variable interaction between the interstitial surfacesand the fluid phases saturating the interstitial spaces.The physical and chemical properties of the fluid phases in contact withthe interstitial surfaces. This involves consideration of the factors of surface, interfacial and adhesiontensions; contact angles; viscosity; density difference between immisciblefluid phases; and other fluid properties. Fine grained, granular, porous materials such as found in petroleum reservoirrock possess characteristics which are expressible bypermeability,porosity, andthe capillary pressure-saturation behavior of immisciblefluids in this medium. These three measurable macroscopic properties dependupon the microscopic properties enumerated above in a manner which defines thecapillary character. T.P. 2594

PROPERTIES OF SANDSTONES AS A REFRACTORY MATERIAL*

AbstractSandstories from Chungking were tested for their properties as a refractory material. Chemical, petrographical, rational, and sieve analyses were made; properties, such as porosity, refractoriness, specific gravity, thermal expansion, and resistance to spalling. were determined; and studies were made on changes in firing up to 1550°C.No inversion of the quartz grains in the rock into tridymite or cristohalite could be detected. The interstitial clay substances fused first, and the quartz grains then dissolved gradually into the glassy matrix on firing at high temperatures.Being free from mineralogical and structural changes, unusually low in thermal expansion and porosity, and good in spalling resistance after firing at high temperatures, sandstones are shown to be an excellent refractory if properly employed. Of the two kinds of rocks, the dense and the porous, the former was found much better in test for refractoriness under load. Prefiring of the material before lining in a furnace structure is desirable to eliminate the permanent expansion and to improve the resistance to spalling in the raw state.