Clay Minerals In Sandstones Research Articles

Genetic analysis and identification of low‐resistivity gas reservoirs of southwestern Sulige gas field in China

AbstractSulige gas field is the largest natural gas producing area in China. Due to the “water blocking” effect, the gas–water layer significantly influences the development of gas reservoirs. The existence of low‐resistivity gas layers in the He 8 member of the Shihezi Formation in the southwestern Sulige gas field makes it challenging to distinguish the gas layers from the gas–water layers using conventional identification methods. To effectively identify the low‐resistivity gas layers, their genetic mechanisms are analyzed by studying their lithology and pore structural characteristics based on the well logging and core experimental data. The low‐resistivity gas layers are main affected by three causes: (1) electrical conductivity of argillaceous laminae in sandstone, (2) additional conductivity of clay minerals, and (3) high bound water saturation caused by the development of micropores and clay minerals in sandstone. Herein, to effectively distinguish the low‐resistivity gas layer from the gas–water layer based on the genetic mechanism of the low‐resistivity gas layer, first, a gas‐bearing index was constructed to characterize the gas‐bearing properties of the reservoir using the neutron logging and density logging curves after eliminating the influence of the dispersed shale. Second, a model to calculate the bound water saturation was constructed by selecting sensitive parameters with respect to the causes of bound water. Then, two plots, namely the gas‐bearing index–natural gamma relative value cross‐plot and the bound water content–porosity cross‐plots, were constructed using the gas testing data, and the identification standard of the low‐resistivity gas and gas–water layers was established. The interactive identification of the two cross‐plots effectively distinguished the low‐resistivity gas layer from the gas‐water layer, thereby providing a basis for understanding the distribution of gas and water in the southwestern Sulige gas field, which may guide further exploration and the deployment of the development well pattern.

Diagenetic Fluid and Its Impact on Sandstone Reservoirs in the Southern Boxing Sag, Dongying Depression, Bohai Bay Basin, China

Diagenesis typically exerts a crucial impact on the formation of high-quality sandstone reservoirs in the Eocene Shahejie Formation, Dongying Depression. To better understand the formation process of petrophysical properties, this research conducts petrographic and geochemical analyses to investigate the nature of diagenetic fluids. Petrographic observations suggest that the dominant cements are carbonate, authigenic quartz, and clay minerals, accompanied with the dissolution of feldspar and calcite. The homogenization temperature of aqueous inclusions in quartz overgrowth usually exceeds 90°C corresponding to the maturity of organic matter. Quartz overgrowths contain higher amounts of CaO and Al2O3 than detrital quartz. This indicates that the siliceous fluid mainly originates from the dissolution of feldspar. Moreover, the conversion of clay minerals also provides trace amounts of silica into pore water during the burial process. Carbonate cements consist of early-stage calcite as well as late-stage Fe-calcite and ankerite. Calcite with relatively higher MnO proportions shows yellow luminescence and dissolution signs. Fe-calcite and ankerite cements have a higher homogenization temperature than that of quartz overgrowth and mainly concentrate in FeO and MgO as well as contain a small amount of Na+, K+, and Sr2+. The rare earth element (REE) pattern of bulk mudstone and carbonate cements as well as C–O isotopic evidences indicate that the diagenetic fluids of carbonate cementation are primarily controlled by the adjacent mudstone, whereas mineral dissolution and altered clay minerals in sandstone provide additional cations for the local reprecipitation of late-stage carbonate. Therefore, diagenetic fluids within sandstone reservoirs are typically subject to alkaline–acid–alkaline conditions and are influenced by internal sources in a closed system. Compaction significantly reduces the pore space of sandstone reservoirs in the Boxing Sag. Carbonate cementation further increases the complexity of pore structure and obeys the principle of mass balance.

SEM-EDX study on authigenic clay minerals in sandstone of Jatiluhur formation

The presence of authigenic clay minerals is usually found in sandstones where these minerals grow in the environment itself. Authigenic clay minerals provide benefits to sandstones, especially to determine the quality of porosity and permeability in sandstones. The samples in this study were collected from an outcrop of measured section at Cipamingkis’ River. The main goal of this study was to understand the presence of authigenic clay minerals in sandstones caused by the diagenetic process using Scanning Electron Microscope and Energy Dispersive X-Ray (SEM – EDX method. The results of this study were kaolinite, smectite, and illite found in very dominant amounts in sandstones as pore linings, pore fillings, replacement, and vug fillings.

Estuarine clay mineral distribution: Modern analogue for ancient sandstone reservoir quality prediction

AbstractThe spatial distribution of clay minerals in sandstones, which may both enhance or degrade reservoir quality, is poorly understood. To address this, clay mineral distribution patterns and host‐sediment properties (grain size, sorting, clay fraction abundance and bioturbation intensity) have, for the first time, been determined and mapped at an unprecedentedly high‐resolution in a modern estuarine setting (Ravenglass Estuary, UK). Results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite, although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary. Fluvial‐supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary. Detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite, chlorite and kaolinite. Chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse‐grained inner estuary dunes and tidal bars. Illite is relatively most abundant (as well as being most crystalline and most Fe–Mg‐rich) in fine‐grained inner estuary and central basin mud and mixed flats. Kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally‐influenced environments. Clay mineral distribution patterns in the Ravenglass Estuary have been strongly influenced by sediment supply (residence time) and subsequently modified by hydrodynamic processes. There is no relationship between macro‐faunal bioturbation intensity and the abundance of chlorite, illite or kaolinite. Based on this modern‐analogue study, outer estuarine sediments are likely to be heavily quartz cemented in deeply‐buried (burial temperatures exceeding 80 to 100°C) sandstone reservoirs due to a paucity of clay grade material (<0·5%) to form complete grain coats. In contrast, chlorite‐enriched tidal bars and dunes in the inner estuary, with their well‐developed detrital clay coats, are likely to have quartz cement inhibiting authigenic clay coats in deeply‐buried sandstones.

Biofilm origin of clay-coated sand grains

The presence of clay-sized particles and clay minerals in modern sands and ancient sandstones has long presented an interesting problem, because primary depositional processes tend to lead to physical separation of fine- and coarse-grained materials. Numerous processes have been invoked to explain the common presence of clay minerals in sandstones, including infiltration, the codeposition of flocculated muds, and bioturbation-induced sediment mixing. How and why clay minerals form as grain coats at the site of deposition remains uncertain, despite clay-coated sand grains being of paramount importance for subsequent diagenetic sandstone properties. We have identified a new biofilm mechanism that explains clay material attachment to sand grain surfaces that leads to the production of detrital clay coats. This study focuses on a modern estuary using a combination of field work, scanning electron microscopy, petrography, biomarker analysis, and Raman spectroscopy to provide evidence of the pivotal role that biofilms play in the formation of clay-coated sand grains. This study shows that within modern marginal marine systems, clay coats primarily result from adhesive biofilms. This bio-mineral interaction potentially revolutionizes the understanding of clay-coated sand grains and offers a first step to enhanced reservoir quality prediction in ancient and deeply buried sandstones.

Characterization of composition and structure of clay minerals in sandstone with ptychographic X-ray nanotomography

Three-dimensional analysis of microporous and fine-grained particles in natural stone is important for understanding their internal fluid flow processes and to allow their internal dynamics to be modeled. These processes are of great interest in oil, gas and groundwater studies, as well as for the weathering of natural building materials. For features above 1μm methods such as X-ray micro-computed tomography (μ-CT) can provide non-destructive, quantitative analysis. Non-destructive 3D imaging at resolutions below 300–400nm, however, has remained a challenge until recent developments at synchrotron beam lines. In this paper we visualize the microstructure of clay mineral samples extracted from two different sandstones at 3D spatial resolutions down to 45nm, using ptychographic X-ray computed tomography (PXCT). Furthermore, the relative humidity of the environment during these experiments was controlled in order to assess its influence on the analyzed samples. Based on these high-quality images, we were able to acquire non-destructively quantitative 3D information on mineral content and distribution, porosity and connectivity of clay mineral clusters inside sandstone.

Species Determination and Spectral Characteristics of Swelling Clay Minerals in the Pliocene Sandstones in Xinghai, Qinghai

X-ray diffraction (XRD) and Fourier infrared absorption spectroscopy (FTIR) were conducted to deepen our research on specific species and spectral characteristics of swelling clay minerals in the Pliocene sandstones in Xinghai, Qinghai province. XRD results show that swelling clay minerals are dominant clay minerals in the sandstones, which can be up to 97% in percentage. XRD patterns show 060 reflections of the samples occur both remarkably at 1.534 Å and 1.498 Å, indicating the samples contain physical mixtures of trioctahedral and dioctahedral swelling clay minerals, respectively. Further treatment of Li-300 degrees C heat and glycerol saturation shows the swelling clay minerals collapse to 9.3-9.9 Å with a partial expansion to -18 Å. This indicates the swelling clay minerals dominate montmorillonite and contain minor saponite. The montmorillonite shows no swelling after Li-300 degrees C heat and glycerol saturation because of Li+ inserting into the octahedral layers, which balances the layer charge caused by the substitution of Mg to Al. FTIR results show the samples are composed of a kind of phyllosilicate with absorbed and structural water, which is in agreement with the results of XRD. Absorbed peaks at 913, 842, 880 cm(-1), corresponding to OH associated with Al-Al, Al-Mg, and Al-Fe pairs, further indicates the minerals are dominant dioctahedron in structure. Meanwhile, absorbed peaks at 625 and 519 cm(-1), corresponding to coupled Si-O and Al-O-Si deformation, indicates parts of Si is replaced by Al in tetrahedron. The spectral characteristics of the samples are against the presence of beidellite and nontronite based on the results of XRD and FTIR, while demonstrating an,existence of montmorillonite. This study, to distinguish the specific species of swelling clay species in clay minerals, would be of great importance when using clay mineralogy to interpret provenance and climatic information.

A strategy for modelling the diagenetic evolution of seismic properties in sandstones

The geometrical distribution of various components in a composite sandstone is decisive for its overall stiffness and seismic velocities. Information about which constituents, for example, are load bearing, dispersed in pore fluid or present as contact cement is, therefore, necessary if the seismic properties are to be modelled reliably. A distribution scheme for quartz cement, K-feldspar and some of the most common clay minerals in sandstones (illite, kaolinite, smectite and chlorite) is suggested on the basis of thin-section observations made by a number of authors. This classification scheme facilitates rock physics modelling as a function of mineral concentrations. A composite rock physics model has also been developed to account for simultaneous combinations of mineral distributions. Well-known mineral reactions are used to make simple models of mineralogy versus temperature (depth) from different starting scenarios, as various minerals tend to follow different and predictable paths during burial and increasing temperature. The mineralogical trends are then entered into the composite rock physics model to produce the diagenetic evolution of seismic rock properties, and the procedure is used to estimate the effective rock properties of sandstones in a well log. The modelling allows deductions to be made about possible mineralogies and their distributions from seismic parameters. Finally, reflection coefficients resulting from sandstones subjected to various diagenetic processes are modelled and analysed. The results show that it is possible to discriminate between reflections emanating from the interfaces of a selection of common diagenetic scenarios.

WORDEN, R. H. & MORAD, S. (eds) 2002. Clay Mineral Cements in Sandstones. International Association of Sedimentologists Special Publication no. 34. viii + 509 pp. Oxford: Blackwell Science. Price £75.00 (paperback). ISBN 1 40510 587 9

WORDEN, R. H. & MORAD, S. (eds) 2002. Clay Mineral Cements in Sandstones. International Association of Sedimentologists Special Publication no. 34. viii + 509 pp. Oxford: Blackwell Science. Price £75.00 (paperback). ISBN 1 40510 587 9 - Volume 141 Issue 1

Thermogravimetry/evolved water analysis (TG/EWA) combined with XRD for improved quantitative whole-rock analysis of clay minerals in sandstones

AbstractCurrent methods of quantitative whole-rock clay mineral analysis of sandstones often provide little more than an estimate of clay mineral abundances, especially where the total clay mineral content is <10 wt% of the sandstone. More accurate determinations of clay mineral abundance in the whole rock can be made by combining thermogravimetry/evolved water analysis (TG/EWA) and X-ray diffraction (XRD) data. The TGA/EWA system incorporates a purpose built thermobalance linked to a water specific infrared detector which is used to measure quantitatively the clay mineral dehydroxylation water evolved from the whole rock when heated from 250°C to 900°C. This gives a measure of the total hydroxyl content of the clay minerals in the whole rock which, when combined with XRD analysis of a separated clay size-fraction, enables individual clay mineral abundances in the whole-rock sample to be determined. Results on artificial sand/clay mineral mixtures prepared with known amounts of different clay minerals (chlorite, illite and kaolinite) show that the accuracy of the combined method is most influenced by the accuracy of the XRD data. Errors associated with TG/EWA were found to be negligible by comparison. A case study is included in which the technique has been used to determine accurately the illite abundance in the Magnus Sandstone Reservoir, Northern North Sea.

Clay Microporosity in Reservoir Sandstones: An Application of Quantitative Electron Microscopy in Petrophysical Evaluation

Clay mineral microporosity in sandstones is measured using computer-assisted image analysis of back-scattered electron micrographs of petrographic sections. Diagenetic kaolinite has a variety of textures with microporosity values ranging from 15 to 61%. Diagenetic chlorite has a generally uniform grain-coating texture and microporosity of about 50%. Fibrous illitic clays are difficult to characterize by the same method (an average value of 63% microporosity was recorded), but analysis of stereo-pair micrographs from scanning-electron microscopy analyses reveals that illite commonly has microporosity of approximately 90%. Clay microporosity data are used to calculate effective pore volumes and volumes of clay-bound water for clay minerals in sandstones. Converting from wei ht percent clay to volume percent clay is important. Microporosity data are valuable input to Vshale evaluation where water saturation is associated with clay mineral type, texture, and volume.

Significance of K-Ar ages of authigenic illitic clay minerals in sandstones and shales from the North Sea

AbstractPetrographic, X-ray diffraction, and microprobe analyses have been used to assess the significance of illite K-Ar ages from sandstones of two North Sea wells. Three closely spaced samples in one well from the upper Statfjord Formation yield similar ages (69-79 Ma) although the illites formed from different precursor minerals. Pore-filling illite in the upper Brent and the Upper Skagerrak Formations from a second well formed by replacing groundmass clays and other detrital minerals. The average layer charge and K+ content increase slightly with depth (0.69-0.80 K+) due to minor reaction and crystal growth during burial diagenesis. These K-Ar ages increase from 15 to 33 Ma within a 500 m depth interval. The K-Ar age vs. depth relationship for these samples corresponds to the burial rate during the middle Tertiary. In examples of extensive illitization of pore-filling clays in sandstones with little subsequent evolution of the clay minerals, the K-Ar ages indicate the age of diagenetic events.In contrast, illitic minerals in shales from the Skagerrak Formation in the second well yield an age (108 Ma) that is much older than the clays in the sandstones, but is still younger than stratigraphic age. The K-Ar ages from illitic clay in shales reported in the literature can get younger, older, or remain essentially unchanged with increasing depth. These age vs. depth trends reflect the complex interplay of crystal growth and dissolution during diagenesis, as well as probable contamination by non-recrystallized detrital illites. The K-Ar ages of illitic clays, therefore, evolve in a different manner in shales than in sandstones.

Origin, Diagenesis, and Petrophysics of Clay Minerals in Sandstones. Sepm Special Publication No. 47 by David W. Houseknecht and Edward D. Pitman, 1992; No. of pages: 282. Price: SEPM members $61.00; non‐members $86.00

Origin, Diagenesis, and Petrophysics of Clay Minerals in Sandstones. Sepm Special Publication No. 47 by David W. Houseknecht and Edward D. Pitman, 1992; No. of pages: 282. Price: SEPM members $61.00; non‐members $86.00

Natural gamma-ray spectrometry in hydrocarbon-bearing sandstones from the Norwegian Continental Shelf

Abstract Concentrations of thorium (Th), uranium (U) and potassium (K) are measured using natural gamma-ray spectrometry (NGS) logs. The precision of NGS measurements in sandstones varies: K measurement is in general moderately good; Th measurement varies with the service company involved; U measurement is unreliable. Concentrations of Th, U and K in standard tables of minerals used commonly in log evaluation are not representative of the actual elemental concentrations found in sandstone minerals. Th/K cross-plots are shown to be unsuitable for the identification of clay minerals in sandstones. Illite cement cannot under normal geological circumstances be identified from the K content of the rock. Authigenic kaolinite has no particular affinity for concentration of Th. Th in sandstones is concentrated predominantly in detrital heavy minerals with up to 200f the total Th present in silt-sized and finer authigenic REE-phosphates and Th salts. Variation in the K content of micas from some Jurassic sandstones demonstrates the need for using formation-specific chemical data for the minerals of interest (micas, feldspars, clay minerals) as input parameters in normative calculations. Appropriate statistical control of the validity of Th, U and K contents for specific minerals is required.

Diagenesis and fluid flow in the San Juan Basin, New Mexico; regional zonation in the mineralogy and stable isotope composition of clay minerals in sandstone

K-Ar DATING OF ILLITE DIAGENESIS IN THE MIDDLE ORDOVICIAN ST. PETER SANDSTONE, CENTRAL MICHIGAN BASIN, USA: IMPLICATIONS FOR THERMAL HISTORY

Clay Mineral Diagenesis in Atoka (Pennsylvanian) Sandstones, Crawford County, Arkansas

ABSTRACT This study concerns the origin and composition of clay minerals in the lower part of the Atoka Formation (Pennsylvanian) of Crawford County, Arkansas. Samples studied are from a 237' core which penetrated a complex interval of interbedded sandstones and shales. Chemical and mineralogical variations in these rocks are primarily related to the post-depositional formation of iron-rich chlorite and destruction of kaolinite. Such effects increase with sandiness of the rocks and are thought to be related to the preferential circulation of formation waters through these relatively porous and permeable sandy sediments. Associated diagenetic phenomena include the formation of authigenic siderite rhombohedra and silica cementation; the latter being related to proximity to shale. The overall pattern of diagenesis is compatible with reducing alkaline conditions. Constancy of inter-element ratios suggests that chemical and mineralogical changes have occurred without gain or loss of a number of elements (Al, B, Ti, Ga, K, Rb) on a whole-rock basis. The most important chemical variation is a reciprocal relationship between iron and aluminum. Detrital interpretations of clay minerals should he made with caution; possible diagenetic effects must also he considered. Clay minerals in sandstone are particularly likely to be of diagenic origin.

Possible Uses of Clay Minerals in Search for Oil

During the last fifteen to twenty years, our understanding of the geologic significance of the clay minerals has increased from nearly zero to the point where we can begin to make some practical application of our knowledge. Following is a brief list summarizing our general knowledge. 1. We know the clay mineral composition of most of the formations in the United States. 2. Pre-Middle Mississippian clay suites are less complex than those in younger sediments. 3. The composition of clay suites may change drastically over an interval of a few feet or remain nearly constant throughout 5,000 feet of section. 4. Both source and environmental information can be obtained. 5. Expanded clays are contracted by burial. 6. The clay suites in limestones are as variable as those in shales. 7. Clay minerals in sandstones are more apt to have been altered after deposition than the clays in other rocks. 8. Once the clay mineral distribution pattern is established, reasonable environmental identifications can commonly be made. 9. If the environmental significance of the clay suites can be established by other means, the clay data can be used independently to identify environments near the control area. 10. Clays can best be used for environmental determinations in young sediments where deposition is relatively slow and environments are materially different. 11. Clay can be used for approximate time correlation where bentonite beds or unconformities are present and where there is a change in source material. 12. Relatively minor clay differences can be correlated for 10-50 miles. In the Upper Mississippian and Lower Pennsylvanian of the Mid-Continent, the clay suites reflect the source areas and tectonic history. Many formations in this interval contain distinctive clay suites which can be used for identification. Detailed correlations can be made by making detailed studies. Both in recent and ancient sediments (shales, limestones, and sandstones) clay mineral suites are related to depositional environments. Clays should be of value in locating the more effective energy barriers. In the recent, both sandstone bars and limestone reefs appear to act as barriers and cause different clay suites to be deposited on the landward and seaward sides. Environmental studies are best made by investigating the whole basin and determining the distribution pattern of the various clay facies. It has been shown that clays can be used to subdivide formations and to locate formation boundaries more accurately than can be accomplished by other techniques. Regional (1,000-2,000 miles) clay mineral zones occur in the Lower and Middle Ordovician and the Upper Mississippian. In the Ouachitas, kaolinite can be used to differentiate the geosynclinal and foreland facies. The relative sharpness of the X-ray diffraction peak of illite affords a good measure of the degree of metamorphism in this area. The available data suggest that there may be some relation between hydrocarbon production and expanded clay minerals. Most of the major producing formations in the United States contain an abundance of expanded clays (montmorillonite, mixed-layer-illite-montmorillonite, and chlorite-montmorillonite). Expanded clays retain their pore water to greater depths of burial than do the other clays. If hydrocarbons are formed at any appreciable depth, the shales containing expanded clays would be the main source of water to carry the hydrocarbons from the shales. Comparison of clay data and velocity data for Tertiary and Paleozoic shales of similar composition (montmorillonite) indicates that the rate of collapse of the expanded clay layers is related to depth and is independent of time. However, the loss of pore water (as shown by density and velocity data) from shale is closely dependent on time.