Diagenetic evolution vis-a-vis reservoir characteristics of Dhosa sandstones, Ler dome, Kachchh, western India (original) (raw)
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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
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 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
2007
The diagenetic processes of the Tabei sandstones in the Tarim Basin include compaction, cementation (quartz overgrowths, calcite, clay minerals and a minor amount of pyrite), and dissolution of the feldspar and calcite cement. Porosity was reduced by compaction from an assumed original 40% to about 22.1%. Cementation reduced porosity to 26.6%. The Tabei sandstones lost a little more porosity by compaction than by cementation. Quartz cementation, especially syntaxial quartz overgrowth, is a major cause of porosity-loss in many reservoirs in moderately to deeply buried sandstone. Calcite cementation played a key role in the porosity evolution of sandstones. At the early stage of burial, the early calcite cement occupied most of the pore spaces resulting in significant porosity. On the other hand, some primary porosity has been preserved due to incomplete filling or the presence of scattered patches of calcite cement. In addition to calcite, several clay minerals, including illite and chlorite occurred as pore-filling and pore-lining cements. The pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurred as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration of penetrability of the reservoir. Calcite cement dissolution was extensive and contributed significantly to the development of secondary porosity.
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.
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.
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.
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.
Journal of Asian Earth Sciences, 2012
The Lower Cretaceous Biyadh Formation in the Masila Basin is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Biyadh Formation more specifically on the diagenesis and relate with reservoir quality, are limited. Based on core samples from one well in the Kharir oilfield, western central Masila Basin, this study reports the lithologic and diagenetic characteristics of this reservoir. The Biyadh sandstones are very fine to very coarse-grained, moderate to well sorted quartzarenite and quartzwacke. The diagenetic processes recognized include mechanical compaction, cementation (carbonate, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cement and feldspar grains. The widespread occurrences of early calcite cement suggest that the Biyadh sandstones lost a significant amount of primary porosity at a very early stage of its diagenetic history. Based on the framework grain-cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-filling clay cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cement and feldspar grains. In addition to calcite, several different clay minerals including kaolinite and chlorite occur as pore-filling and pore-lining cements. Kaolinite largely occurs as vermiform and accelerated the minor porosity loss due to pore-occlusion. Chlorite coating grains helps to retain primary porosity a by retarding the envelopment of quartz overgrowths. Porosity and permeability data exhibit good inverse correlation with cement. Thus, reservoir quality is controlled by pore occluding cement. Diagenetic history of the Biyadh sandstones as established here is expected to help better understanding and exploitation of this reservoir. The relation between diagenesis and reservoir quality is as follows: the initial porosity was decreased by compaction and cementation and then increased by dissolution of early calcite cement and feldspar grains. The reservoir quality is also affected by depositional environment controls of grain size, sorting and matrix. Thus, best good quality reservoir rocks were deposited in braided river channels environment, where no inhibited authigenic clays and high percentages of detrital quartz.