Petrography and diagenetic evolution of the Barail sandstones of Naga Schuppen belt, North East India: implication towards reservoir quality (original) (raw)
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Arabian Journal of Geosciences, 2018
The detrital mineralogy as well as diagenetic characters of the Dhosa Sandstone Member of Chari Formation exposed at the Lerdome, south of Bhuj was studied. In order to assess the potential of the Dhosa Sandstone as a reservoir, it is substantial to understand the diagenetic processes that are controlled largely by post-depositional cementation and compaction in addition to framework composition and original depositional textures. The petrologic analysis of 33 thin sections was carried out to discern primary composition and diagenetic features including primary and secondary porosity patterns. Monocrystalline quartz dominates the detrital mineralogy followed by polycrystalline quartz. Among the polycrystalline variety recrystallized metamorphic quartz surpasses stretched metamorphic quartz in terms of abundance. Feldspars comprise microcline and plagioclase where the former is dominant over the latter. Orthoclase too comprises a very small percentage. Mica, chert, rock fragments, and heavies form the remaining detrital constituent in descending order of their constituent percentage. The diagenetic precipitates are mainly carbonate (8.30%) and iron (7.80%) followed by clay (0.66%) and silica (0.88%) that are minor constituent of the total cementing material. The main paragenetic events identified are early cementation, mechanical compaction, late cementation, dissolution, and authigenesis of clays. The overall reservoir quality seems to be controlled by compaction and authigenic carbonate cementation. The minus cement porosity average 29.4%. The porosity loss due to compaction is 21.92% and by cementation is 29.71%. The loss of original porosity was due to early cementation followed by moderate mechanical compaction during shallow burial. Preservation of available miniscule primary porosity was ascribed to dissolution of carbonates and quartz overgrowth which resisted chemical compaction during deep burial. The studied sandstones may have low reservoir quality owing to existing porosity of less than 9%. More carbonate dissolution and its transformation in dolomite in sub-surface condition and macrofracture porosity may result in enhanced secondary porosity and good diagenetic traps.
Research Square (Research Square), 2023
The Neoproterozoic Bhander Group, the youngest and most widely distributed group of Upper Vindhyans, consists of about 1000 m thick succession of sandstone, shale, and limestone. Petrographic investigations reveal that the Bhander Sandstones are mineralogically mature and classified as quartzarenite and sublitharenite type, which is composed of varieties of quartz with scarcity of feldspar, lithic fragments, micas, and heavy minerals. The average framework composition of the Lower Bhander Sandstone is Qt 98.68 F 0.10 L 1.22, and Upper Bhander Sandstone is Qt 95.92 F 0.12 L 3.96. The provenance, tectonic setting and diagenesis of Bhander Sandstones are evaluated using integrated petrographic studies. Analysis reveals detrital derivation from granitic and metamorphic Precambrian basement source rocks of a craton interior with a minor quartzose recycled sedimentary rock. A scarcity of feldspar and lithic fragments suggests intense chemical weathering in a warm and humid paleoclimate. The diagenetic processes recognised include compaction, cementation, and dissolution, affecting the sandstone porosity, thereby directly affecting reservoir quality. Mechanical compaction, cements, authigenic clays, and dissolution and modification of unstable clastic grains are the major diagenetic components identified based on the framework grain-cement relationships. Compaction was more effective than cementation in affecting primary porosity. Cementation decreased porosity and permeability drastically. Kaolinite and silica (quartz) overgrowth are found as pore-filling and lining cements. Kaolinite fills pore spaces, reducing the porosity and permeability. Secondary porosity developed as a result of partial to complete feldspar dissolution. The diagenetic signatures observed in the Bhander Sandstones are suggestive of deep burial conditions. The reservoir quality of the studied sandstones is degraded by authigenic clay minerals and cementations but enhanced by the alteration and dissolution of unstable grains.
2019
In Central India the Upper Kaimur Subgroup of Vindhyan Supergroup, primarily consists of three lithounits-Dhandraul Sandstone, Scarp Sandstone and Bijaigarh Shale. The framework grains, mineralogy, matrix, pore properties and cements were identified. Average framework composition of the texturally super-mature Dhandraul Sandstone is Qt 99 F 0.1 L 0.8 and texturally less mature, Scarp Sandstone is Qt 99 F 0.2 L 0.8. The important diagenetic components identified based on the framework grain-cement relationships are mechanical compaction, cements, authigenic clays and dissolution and alteration of unstable clastic grains and tec-tonically induced grain fracturing. The early to intermediate stage of the diagnostic realm e.g., mechanical compaction, cementation, dissolution, and authigenesis of clays (dominantly kaolinite, mixed illite-smectite and minor illite). Mixed illite-smectite and illite occur as pore-filling and or lining during authigenic phases. Kaolinite and silica (quartz) overgrowth occur as pore-filling and lining cements. Compaction played an added role than the cementation in modifying the primary porosity. Cementation drastically reduced the porosity and permeability. Kaolinite fills pore spaces and caused reduction in the porosity and permeability of the sandstone. Secondary porosity development occurred due to partial to complete dissolution of feldspar. The diagenetic signatures observed in the Upper Kaimur Subgroup Sandstones are suggestive of intermediate burial (2-3 km depth). The reservoir quality of the studied sandstones is reduced by authigenic clay minerals (kaolinite, mixed illite-smectite and minor illite), cementations, and on other hand, it is increased by alteration and dissolution of unstable grains.
In this paper petrographic and heavy mineral account of the Barail sandstones of Zubza village area is presented. The sandstones are dominated with Quartz arenite. Few other petrographic types are Argillaceous Siltstone, Laminated Siltstone, Micaceous Quartz Arenite and Lithic Glauconitic Arenite. The modal composition reveals that the percentage occurrences of different constituents of these Barail sandstones range as Quartz (39.85% to 64.10%, Feldspar 5.27% to 8.25%, and Rock fragments 4.53% to 14.25%). However the rich Monocrystalline quartz implies their derivation from intrusive igneous rocks. The Predominance of unit quartz and undulose quartz collectively corroborate the dual sources of low rank metamorphic, and plutonic sources of variable pressure effects. QFL triangular plot infers the derivation of the sandstones from recycled orogenic sources. QmFRt triangular plot shows that the provenance of these Barail sandstones were mainly of mixed and dissected arc types. However, few of them also show their derivation from quartz arenite recycled origin.
Arabian Journal of Geosciences, 2019
The plethora of micro (μm)-to-mega (≥ 10 to ≤ 100 m) scale heterogeneities in marginal marine siliciclastic reservoirs makes their petrophysical analysis often cumbersome, and thus yield unrealistic reservoir parameters. Micro-scale heterogeneities typically occur at the microscopic scale, while the mega-scale is observable at the outcrop scale. A good understanding of the possible heterogeneities within sandstone reservoirs can enhance their quality assessment significantly. In this study, heterogeneities in analogue marginal marine sandstones of Nyalau and Balingian formations, NW Borneo, were qualitatively characterised using integrated field geology and geochemical analyses. The outcrops are typically characterised by an upwardcoarsening sequence, consisting of sandstone and argillaceous lithounits. The sandstones are moderate-to well-sorted, fine-to medium-grained with varying kurtosis and skewness. Estimated matrix composition in thin section ranges between 15 and 67%, thus classifying the sandstone as feldspathic litharenites to sublithearenite. Skolithos (Ophiomorpha) and Planolites are the commonly observed ichnofacies with bioturbation index of 0 to 90%. Three mineralogical relationships (denoted as MF) were defined based on quartz-feldspar-clay contents. Of these, reservoir units characterised by the MF-1 have better reservoir potential than the other two. Scanning and electron microscopy (SEM) revealed that the secondary pores created from grain dissolutions are partly to completely filled by networks of illite strands, kaolinite/dickite sheets, chlorite flakes, pyrite and very rarely laumontite. An integration of SEM, XRD and mineralogical evolution trend suggests that most of these pore-modifying minerals are of authigenic origin. This research concluded that pore-destroying alterations predominate pore enhancement modifications in the sandstones. Hence, fluid flow parameters and by implication production from the sandstone may be significantly impacted in a negative sense.
Petrography and Provenance of Surface Barail Sandstones, Kohima, Nagaland, India
Geological domains in North-Eastern India evolved though time after the rupture of the Gondwanaland. Collision of the Indian and the Burmese plates took place during the middle part of Cretaceous. Evolution of the Palaeogene Barail trough, Neocene Surma and Tipam Groups took place gradually. The Barail trough originated at the active margin of the Indo-Burmese plate convergence. The present study evaluates the petrographical studies of sandstone samples from Barail Group occurring in Kohima, Nagaland. It provides informations about mineralogical variations, and provenance of the area. Through the modal analysis it is clear that the sandstone samples fall mostly in the field of Quartz arenite, and point out a continental block provenance field. Framework grains are sand-sized to silt-sized particles of mainly detrital origin. The most common detrital grains are monocrystalline quartz (39.0-58.0%); polycrystalline quartz (1.8-9.6%); K-feldspar (2.7-7.2%); plagioclase (1.4-8.5%); collophane (0-3-3.1%); muscovite (0-1.5%); lithic fragments (2.1-10.4%); heavy minerals (trace). Lithic fragments are predominantly highly siliceous and finely textured. Among the main detrital framework grains, quartz constitutes. Sandstones encountered in the studied Sections have been classified as Quartz arenite, Laminated siltstone, Argillaceous Silstone and Lithic Glauconitic arenite in order of abundance.Further this study supports a humid climate during the deposition of the Barail Group of sediments.
Journal of the Geological Society of India, 2018
Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effects of diagenetic process such as compaction, cementation and dissolution on reservoir properties. The average framework composition of Ridge sandstone is Q 80 F 17 L 3 , medium-to coarse grained and subarkose to arkose. Syndepositional silty to clayey matrix (3% average) is also observed that occurs as pore filling. The diagenetic processes include compaction, cementation and precipitation of authigenic cements, dissolution of unstable grains and grain replacement and development of secondary porosity. The major cause of intense reduction in primary porosity of Ridge sandstone is early cementation which include silica, carbonate, iron, kaolinite, illite, smectite, mixed layer illite-smectite and chlorite, which prevents mechanical compaction. The plots of COPL versus CEPL and IGV versus total cement suggest the loss of primary porosity in Ridge sandstone is due to cementation. Cements mainly iron and carbonate occurs in intergranular pores of detrital grains and destroys porosity. The clay mineral occurs as pore filling and pore lining and deteriorates the porosity and permeability of the Ridge sandstone. The reservoir quality of the studied sandstone is reduced by clay minerals (kaolinite, illite, smectite, mixed layer illitesmectite, chlorite), carbonate, iron and silica cementation but on the other hand, it is increased by alteration and dissolution of the unstable grain, in addition to partial dissolution of carbonate cements. The potential of the studied sandstone to serve as a reservoir is strongly related to sandstone diagenesis. INTRODUCTION Sandstone diagenesis is of great importance in understanding the reservoir quality of sandstone. The reservoir quality is controlled by composition (Ehrenberg, 1990; Bloch, 1991), texture (Scherer, 1987; Atkins and McBride, 1992) and diagenetic processes (Lundegard, 1992). Diagenesis is also controlled by factors such as texture, detrital composition, environment of deposition and associated lithology (Burley et al., 1985; Morad et al., 2000). The detrital composition can influence the reservoir quality of sandstone by conditioning the pathway of both physical and chemical diagenesis (Bloch, 1994). The intraformational variations in the detrital composition of sandstone results in significant heterogeneity in reservoir quality of sandstone. The importance of compaction, both mechanical and chemical is regarded as less capable than cementation (Houseknecht, 1987; McDonald and Surdam, 1984; Lundegard, 1992). The effect of cementation on sandstone porosity is estimated easily i.e. the pore spaces are filled with cement and are observed in sandstone (Ehrenberg, 1995). Kachchh basin, in general constitutes a potential site for petroleum exploration. Scientists have worked on the prospects of hydrocarbon in Kachchh basin (Biswas and Deshpande, 1983). However, the understanding of the diagenetic controls on the reservoir of the Jurassic Jumara dome Ridge sandstone from the Kachchh basin is not thoroughly studied. Reservoir quality is one of the key controls on the efficient exploration of reservoir, and therefore, it is important to have a detailed understanding of the various diagenetic controls and their effects. The aim of the present study is to have a detailed diagenetic analysis. The analysis was undertaken to provide data that will help in understanding diagenesis with a goal on various diagenetic controls and reservoir quality of Ridge sandstone. GEOLOGICAL BACKGROUND The Kachchh basin is a pericratonic basin in the west of Indian peninsula (Biswas, 1987). The Kachchh basin covers entire Kachchh district in Gujarat state and extends between latitude 22°30' and 24°3 0' N and longitude 68° and 72° E (Fig.1). The Kachchh basin was formed due to rifting and counters clockwise rotation of Indian plate in the late Triassic/early Jurassic (Biswas, 1987). The basin is bordered by subsurface Nagarparker Massif in the north, Radhanpur-Barmer arch in the east and Kathiawar uplift towards the south (Biswas, 1982). Mesozoic sediments in the Kachchh basin range in age from Bajocian to Albian (Table 1) lay unconformably on the Precambrian basement (Bardhan and Datta, 1987). Mesozoic sediments are the rift fill sediments and constitute the major part of the basin fill (Biswas, 2002). Basin configuration was controlled by primordial fault pattern in the basement rocks (Biswas, 1977). The Mesozoic rocks are exposed in the Kachchh mainland, Wagad, Bela, Khadir, Patcham and Chorar islands in the great Rann of Kachchh ranging in age from middle Jurassic to lower Cretaceous. In the Kachchh mainland at Jumara dome mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic dominating Chari Formation (Bathonian to Oxfordian) are exposed. Jumara hills lie on the western flank of Kachchh mainland near great Rann of Kachchh and these hills form a dome which is doubly plunging anticline. Jumara dome located nearly 80 km NW of Bhuj. Geologically, the Jumara dome is famous locality in the Mesozoic strartigraphy of Kachchh for its abundant mega fossils and good Jurassic exposures. The lower part of the Jumara dome is represented by the Jumara Coral Limestone Member of Jhurio Formation, followed upward by the Echinoderm Packstone Member of Jhurio Formation, above this Spongy Limestone Member of Patcham Formation followed by Grey Shale Member of Chari Formation followed by Ridge Sandstone Member of Chari Formation overlain by Gypsiferous Shale Member of Chari Formation and on the top Dhosa Oolite Member of Chari Formation (Fig.2). SAMPLES AND METHODOLOGY The study is based on a total twenty samples representing different levels of measured litho-stratigraphic section at Jumara dome (Fig.2). The analytical techniques applied are thin section petrography, scanning
Arabian Journal of Geosciences, 2016
The Maastrichtian Pab Sandstone and the Danian Khadro Formation are among the major reservoirs of the region but are considered to be tight and are therefore poorly evaluated. A 551-m-thick section of the Pab Sandstone and 128-m-thick section of the Khadro Formation are measured and logged in detail. The measured units mainly composed of thin-to thick-bedded sandstone with subordinate mudstone and occasional marls that were deposited in the western passive margin of the Indian Plate. Eight and four depositional facies have been identified in the Pab and Khadro Formations, respectively, and are grouped into pro-delta, delta-front, and delta-plain facies associations which were deposited in fluvial-wave-dominated deltaic settings. Thirty-two samples of sandstones from Pab Sandstone and 20 from Khadro Formation are collected for reservoir and petrographic studies. The sandstone of studied formations are classified as quartz aernite, subarkosic, sublitharenite, and wackes. These are fine to coarse grain, subangular to rounded, and poorly to moderately sorted. The intense burial diagenesis resulted in compaction, extensive cementation, and authigenic mineralization which cause low values of porosity/permeability. Cements have filled all the available pore spaces and clay minerals block pore throats, thus resulting in major destruction of porosity and permeability. The late stage dissolution of unstable framework grains and cements has resulted in appreciable increase in secondary porosity. The petrographic studies and plug porosity/permeability results of outcrop samples suggest that laterally continuous and vertically stacked thick sandstone sequences of delta-plain and delta-front facies associations possess good values of porosity.
Diagenetic history of the Surma Group sandstones (Miocene) in the Surma Basin, Bangladesh
Journal of Asian Earth Sciences, 2012
This study examines the various diagenetic controls of the Miocene Surma Group sandstones encountered in petroleum exploration wells from the Surma Basin, which is situated in the northeastern part of the Bengal Basin, Bangladesh. The principal diagenetic minerals/cements in the Surma Group sandstones are Fe-carbonates (with Fe-calcite dominating), quartz overgrowths and authigenic clays (predominantly chlorite, illite-smectite and minor kaolin). The isotopic composition of the carbonate cement revealed a narrow range of d 18 O values (À10.3‰ to À12.4‰) and a wide range of d 13 C value (+1.4‰ to À23.1‰). The d 13 C VPDB and d 18 O VPDB values of the carbonate cements reveal that carbon was most likely derived from the thermal maturation of organic matter during burial, as well as from the dissolution of isolated carbonate clasts and precipitated from mixed marine-meteoric pore waters. The relationship between the intergranular volume (IGV) versus cement volume indicates that compaction played a more significant role than cementation in destroying the primary porosity. However, cementation also played a major role in drastically reducing porosity and permeability in sandstones with poikilotopic, pore-filling blocky cements formed in early to intermediate and deep burial areas. In addition to Fe-carbonate cements, various clay minerals including illite-smectite and chlorite occur as pore-filling and pore-lining authigenic phases. Significant secondary porosity has been generated at depths from 2500 m to 4728 m. The best reservoir rocks found at depths of 2500-3300 m are well sorted, relatively coarse grained; more loosely packed and better rounded sandstones having good porosities (20-30%) and high permeabilities (12-6000 mD). These good quality reservoir rocks are, however, not uniformly distributed and can be considered to be compartmentalized as a result of interbedding with sandstone layers of low to moderate porosities, low permeabilities owing to poor sorting and extensive compaction and cementation.
Petrophysical and petrographic characteristics of Barail Sandstone of the Surma Basin, Bangladesh
Journal of Petroleum Exploration and Production Technology, 2021
The Barail sandstone in the Surma Basin is a medium- to coarse-grained pinkish-colored rock exposed near the northeastern margin of Bangladesh. In this study, we evaluated the reservoir quality of the Barail sandstone based on its petrophysical and petrographic characteristics. Petrophysical analyses of outcropped samples showed that sandstones are made up of 16.48% porosity and 132.48 mD permeability. Sandstone density ranges from 1.94 g/cm3 to 2.37 g/cm3, with a mean value of 2.12 g/cm3, shown as moderately compacted sandstone. Integrated data such as bulk density, porosity, permeability, Rock Quality Index (RQI), Normalized Porosity Index (NPI), Flow Zone Indicator (FZI), compressive strength, etc. with their relationships indicate that Barail sandstone owing characters to become a good petroleum reservoir. The rock samples consisted mainly of quartz with an insignificant amount of rock fragments and plagioclase feldspar and are categorized as sub-arkose to sub-litharenite. The r...