Petrography and Diagenetic Evolution of the Proterozoic Kaimur Group Sandstones, Son Valley, 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.
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
Journal of Asian Earth Sciences, 2011
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
Current Science
Rock-thin section, scanning electron microscopy and X-ray diffraction analyses have been employed to describe in detail the mineralogical constituents, diagenetic alterations and their impact on reservoir quality of Oligocene Barail sandstones of Naga Schuppen belt, North East India. The Barail Group comprises of alternate beds of hard and compact sandstones with siltstone, shale, carbonaceous shale, and a few thin intermittent coal seams in the upper part of the rock sequence. Petrographic analysis indicates that quartz (42.02-55.02%) is the most dominant mineral constituent followed by rock fragments (6.85-15.67%) and feldspars (0.00-1.97%) with different types of cement in the studied sandstones. Quartz overgrowth, formation of pseudo matrix, authigenic growth of secondary minerals and precipitation of clay within the pore spaces tend to reduce the primary and secondary porosities of the rocks. However, in certain samples, the grain coating restricts or hinders cementation and preserves porosity during deep burial, but decreases permeability at pore throats. Partial dissolution and intragranular fracturing of the framework minerals provide sites for pore growth. Pyrite framboids and iron oxides inhibit quartz cementation, but infill pore spaces. The present study shows that original pore morphologies, as well as secondary porosities within the sandstones tend to be destroyed to a large extent by the diagenetic processes.
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.
Journal of Petroleum Geology, 2010
This paper assesses the diagenetic history of potential fluvial hydrocarbon reservoir rocks deposited within incised valley systems of the Lower Carboniferous Marar Formation in western Libya. Outcrop data were collected in the Tinedhan Anticline, located at the southern margin of the Ghadames Basin. Four discrete intervals with channelized sandstones were identified in a section dominated by alternating offshore mudstones and shallow-marine clastics. The incised channels were cut during major sea-level lowstands, and filled by fluvial sandstone packages up to 50 m thick. Fifty-eight samples from four different localities, representing three lowstand systems tracts, were analysed to obtain a statistically meaningful mineralogical and compositional dataset.In addition to burial compaction, three main diagenetic events influenced the reservoir quality of the sandstones. Firstly, early eodiagenesis involved kaolinitization of plagioclase grains. This began before subsequent calcite cementation, probably as a result of flushing by meteoric pore-waters. The deformation of kaolinite during later compaction resulted in the formation of pseudomatrix which further reduced porosity and permeability. Kaolinite is commonly transformed to illite at temperatures above 140°C in the presence of K-feldspar. Although K-feldspar was recorded in the samples, no illite was observed, suggesting that the Lower Carboniferous strata in the study area were not buried in excess of approximately 3.5 km.The second diagenetic phase was the precipitation of calcite cement, present either dispersed throughout the sandbodies or as concretions up to 2 m across, in both cases reducing reservoir quality. The high intergranular volumes (IGV) of calcite-cemented sandstones (ranging between 35% and 40%) suggest that cementation occurred at burial depths of <500 m. Sandstones without calcite cement have lower IGV of between 17% and 25% as a result of mechanical and chemical compaction. Stable C and O isotope analysis of the calcite cement also supports precipitation at shallow burial depths, indicating a meteoric pore-water source for the calcite. The third and final diagenetic stage was partial chloritisation of kaolinite during meso-diagenesis. The elevated temperatures required for this transformation indicate burial to a minimum depth of approximately 2.5 km, which is consistent with the compaction data.Despite these diagenetic effects, the fluvial sandstones have an average porosity of 12%, with a range from 0.5% up to 25%. Permeability measurements on four sandstone samples indicate that the development of pseudomatrix did not reduce permeability significantly.
2018
Framework mineralogy and heavy mineral analysis of Proterozoic Upper Kaimur Group Sandstones of the Vindhyan basin, Son Valley have been investigated on composition, provenance and tectonic setting. The studied sandstones are quartzarenite to sublitharenite in composition with high quartz, low feldspar, mica and low to moderate amounts of lithic fragments of metamorphic and sedimentary rocks. The detrital modal compositions of these sandstones reveal that these sandstones belong to the continental block, recycled orogen, rifted continental margin tectonic regime with maturity and stability of the source region. The characteristic heavy minerals are zircon, tourmaline, rutile, epidote, biotite, chlorite, staurolite, hornblende, hypersthene, garnet and opaques. The non-opaque heavy mineral assemblage of the sandstone is dominated by zircon, tourmaline and rutile (ZTR) suggests a recycled sedimentary source. Though heavy mineral suites of all the sandstone samples are by and large similar, but differences are seen in their frequencies of heavy minerals in a vertical succession. Mineralogical maturity coupled with characteristic heavy mineral associations is consistent with northern and northwestern palaeoflow and tectonic evolutionary history of the region that indicates Mahakoshal Group and Chhotanagpur granite gneiss present in the southern side of the study area show the source of the Upper Kaimur Group rocks.
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.
Diagenetic Features of Jurassic Fort Member Sandstone, Jaisalmer Formation, Western Rajasthan
Jaisalmer Formation consists of 360m thick succession of medium to coarse grained sandstones with interbeds of shale, claystone and occasional lignite that rest over Lathi Formation, is the basal part of the Jaisalmer basin. The rocks are exposed amidst desert, low mounds and shallow stone quarries. Sandstones were deposited in shallow marine to deltaic environments. The studied sandstones consist of abundant quartz followed by feldspar, mica, chert, rock fragments and heavy minerals. The study mainly deals with identification of various diagenetic features such as compaction, cementation and porosity evolution. During mechanical compaction rearrangement of grains took place and point, long and suture contacts were formed. The sandstones are cemented by iron oxide, silica overgrowth, carbonate and clay. Porosity has developed due to dissolution of iron, carbonate cement and feldspar grains. Dissolution and alteration of feldspar, lithic fragments and pressure solution were the main source of quartz cements. The sandstones show good amount of existing optical porosity with an average of 7.19%. Porosity reduction is mainly due to early stage of mechanical compaction and subsequent pervasive calcite and iron oxide cementation. Further, porosity reduced due to deposition of clay cement.
European Scientific Journal, ESJ, 2013
The Neogene Siwalik sequence of western Arunachal Pradesh comprises northward dipping thrust sheets structurally below the Main Boundary Fault (MBT) and above the Main Frontal Thrust (MFT). The Sub-Himalayan fold and thrust belt comprises four lithotectonic units between MBT and MFT. From oldest to the youngest these units are Kimi, Dafla, Subansiri and Kimin Formations. The Kimi Formation is equivalent to Lower Siwalik; Dafla and Subansiri formations are equivalent to the Middle Siwalik, while the Kimin Formations represent Upper Siwalik respectively. In the Kameng sector, Tipi Thrust is interpreted to be an intraformational thrust within Subansiri Formation; the Dafla Formations are trusted over the Subansiri Formation relatively at a higher structural level. Compaction and subsequent strong horizontal north to south compression led to the development of numerous zones of cataclasis in the Dafla and Subansiri sandstones. Earlier diagenetic fabrics in the sandstones have been modified considerably due to subsequent development of deformational grain scale microstructures under compression. The Pure Compaction Bands were formed in the initial stage under raised porosity and permeability. These are transformed to Shear Enhanced Compaction Bands and subsequently to Compactional Shear Bands when deformation assumes a simple shear mode under low porosity and permeability value. Higher degree of compaction is evident in the Dafla sandstone compared to that of the Subansiri sandstone which inferred on the basis of the type of the grain contacts, grain packing, frequency of pressure solution seams and segregated micaceous bands.