Conditions of Compaction and Development of Diagenetic Microstructures in the Dafla and Subansiri Sandstones, Westernarunachal Pradesh, India (original) (raw)
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Porosity and grain size controls on compaction band formation in Jurassic Navajo Sandstone
Geophysical Research Letters, 2010
1] Determining the rock properties that permit or impede the growth of compaction bands in sedimentary sequences is a critical problem of importance to studies of strain localization and characterization of subsurface geologic reservoirs. We determine the porosity and average grain size of a sequence of stratigraphic layers of Navajo Sandstone that are then used in a critical state model to infer plastic yield envelopes for the layers. Pure compaction bands are formed in layers having the largest average grain sizes (0.42-0.45 mm) and porosities (28%), and correspondingly the smallest values of critical pressure (∼22 MPa) in the sequence. The results suggest that compaction bands formed in these layers after burial to ∼1.5 km depth in association with thrust faulting beneath the nearby East Kaibab monocline, and that hardening of the yield caps accompanied compactional deformation of the layers. Citation: Schultz, R. A., C. H. Okubo, and H. Fossen (2010), Porosity and grain size controls on compaction band formation in
Proceedings of the National Academy of Sciences, India Section A: Physical Sciences, 2013
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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.
Tectonophysics
We present evidence for the existence of tabular zones of localized deformation in aeolian sandstone, that accommodate pure compaction. In this sense they are analogs for anticracks or closing mode I fractures such as pressure solution surfaces or stylolites. The so called "compaction bands" are exposed in outcrops of the Jurassic Navajo Sandstone in the Kaibab monocline, Utah. They are characterized by lack of shear offset across their plane, volume loss, micro fracturing and very little grain crushing or comminution. Based on their geometry, two kinds of compaction bands are distinguished: the first kind is 0.5-1.5 cm thick and fairly straight over lengths of about 5-10 m. The second kind is 0.1-0.5 cm thick over lengths up to 2 m, and is conspicuously crooked with wavelengths of 1-5 cm and amplitudes of a few mm to a few cm.
Petroleum Science, 2015
In order to analyze the factors influencing sandstone mechanical compaction and its physical property evolution during compaction processes, simulation experiments on sandstone mechanical compaction were carried out with a self-designed diagenetic simulation system. The experimental materials were modern sediments from different sources, and the experiments were conducted under high temperature and high pressure. Results of the experiments show a binary function relation between primary porosity and mean size as well as sorting. With increasing overburden pressure during mechanical compaction, the evolution of porosity and permeability can be divided into rapid compaction at an early stage and slow compaction at a late stage, and the dividing pressure value of the two stages is about 12 MPa and the corresponding depth is about 600 m. In the slow compaction stage, there is a good exponential relationship between porosity and overburden pressure, while a good power function relationship exists between permeability and overburden pressure. There is also a good exponential relationship between porosity and permeability. The influence of particle size on sandstone mechanical compaction is mainly reflected in the slow compaction stage, and the influence of sorting is mainly reflected in the rapid compaction stage. Abnormally high pressure effectively inhibits sandstone mechanical compaction, and its control on sandstone mechanical compaction is stronger than that of particle size and sorting. The influence of burial time on sandstone mechanical compaction is mainly in the slow compaction stage, and the porosity reduction caused by compaction is mainly controlled by average particle size.
2009
Compaction energies calculated in this paper for the Utah bands, G c = 55-120 kJ/m 2 , and for the Nevada bands, G c = 30-60 kJ/m 2 , are consistent with those estimated from laboratory experiments despite major differences in band length, thickness, degree of grain fracturing, and remote stress state. Using the field measurements of bands from both sites in the recently proposed inverse relation between the magnitude of remote bandnormal compression and compaction band thickness predicts values of band-normal compression of 24-30 MPa for the Utah bands and 31-62 MPa for the Nevada bands. Given that compaction bands at both sites are steeply dipping, these values correspond to a regional tectonic compression oriented subhorizontally at the time of band growth. The results suggest that the compaction bands formed at relatively shallow paleodepths of 0.92-1.3 km at the Utah site and 0.54-1.1 km at the Nevada site, in accord with estimates of the thickness of overlying stratigraphic cover during Sevier-Laramide deformation at both sites. Growth of compaction bands at both field sites was likely facilitated by favorable host rock properties (well-sorted, coarse-grained, high-porosity sandstone sequences) deformed within a thrust faulting tectonic environment.
Tectonophysics, 2009
This study combines field observations and laboratory analyses to identify and characterize predominantly bed-parallel compaction bands in the aeolian Aztec Sandstone exposed in the Valley of Fire State Park, Nevada. These bed-parallel compaction bands display morphological and geometrical characteristics of deformation bands of various modes previously described in the literature, such as positive relief, echelon geometry, "bridge" and "eye" structure, and zonal occurrence. Portions of some bands cross-cut sedimentary layers, thereby distinguishing themselves from depositional bedding. Laboratory image analyses of several samples collected from bed-parallel bands, using a computational rock physics algorithm, show that their porosities are less than half that of the host rock and their permeability is nearly one order of magnitude less. In addition, the study area includes compaction bands that have dip angles ranging from sub-horizontal to greater than 20°. Parts of these bands have even higher dip angles and show evidence for increasing intragranular fracturing and shearing as the band inclination increases. We attribute this variation to shearenhanced compaction, a mechanism proposed earlier by experimental rock mechanists. One of the implications of the occurrence of localized compaction in the form of discrete bands parallel to flat-lying and low-angle bedding is that it provides an alternative or an additional mode to a vertically continuous compaction in loose or poorly cemented sediments. If pervasive, bed-parallel compaction bands with significantly lower porosity than that of the surrounding undeformed rock should result in a significant heterogeneity and vertical anisotropy in seismic velocities and hydraulic properties of granular rocks.
The Glauconitic sandstone is well exposed in the Newari area of Sonbhadra district of Uttar Pradesh, India. Conjugate pairs of kink bands are confined within the laminated sandstone and are present half km west of Newari near the confluence of a tributary with the Son river. The conjugate kink bands are plunging at 13 0 and 36 0 in SE (S58 0 E) and NE (N56 0 E). This shows that ephemeral compressional stress regime was responsible for the development of conjugate set of kink bands. The stress axis would have been oriented from NE-SW direction. A major fault F1 passes through the glauconitic sandstone in the west of the Newari village. This fault is a reverse fault and strikes at N25ºW -S25ºE. Another fault F2 oblique to F1 passes in the direction N70ºE-S70ºW. In view of the fact that the kink bands are confined within the laminated sandstone, it is inferred that they have been formed as a result of penecontemporaneous deformation and suggest seismic activities that might have occurred around 1080±40 Ma ago as a result of activation of the faults present in the Newari area of the Sonbhadra district, Uttar Pradesh, India those may be companion faults of the Son-Narmada Fault system.
Effects of pre-existing faults on compaction localization in porous sandstones
Tectonophysics, 2018
The formation of deformation bands can significantly modify the strength and transport properties of porous sedimentary rocks. Among the different types of deformation bands, compaction bands exhibit porosity reduction with little to no shear displacement. Natural compaction bands have previously been reported and studied in only a few areas. They often coexist with faults and other localized deformation structures. We mapped the geometrical relation between compaction bands, shear bands and faults in Lower Cretaceous porous sandstone at Makhtesh Katan, Israel. To understand the effect of pre-existing faults on the formation of compaction bands, we conducted deformation experiments on pre-faulted Bentheim sandstones. These experiments produced compaction bands consistently intersect the pre-existing fault. To gain better mechanical understanding of the observed band geometry, we also carried out three-dimensional (3D) numerical simulations with the input elastic moduli and yield strength well-constrained from the deformation experiments. We demonstrated that the formation of deformation bands is dictated by stress concentrations associated with the pre-existing fault. Frictional slip along the heterogeneous fault plane can produce a local stress concentration that would be responsible for further localized damage and the development of deformation zones. When fault slip is restricted (a possible result of high confinement), compaction bands initiate at high stress concentration sites resulting from geometrical irregularities of the fault. Finally, using a plane-strain twodimensional (2D) linear-elastic model with the geometry of the faults mapped in the outcrop, we were able to provide a mechanical explanation of the distribution for deformation bands observed at the Makhtesh Katan study area.
Conditions and implications for compaction band formation in the Navajo Sandstone, Utah
Journal of Structural Geology, 2011
Observations from quartz-rich eolian Navajo Sandstone in the Buckskin Gulch site in southernmost Utah show that pure compaction bands only occur in sandstones where current porosity > 0.29 AE 3, permeability > 10 AE 7 darcy, and grain size > 0.4 mm e properties restricted to the lower and most coarsegrained and well-sorted parts of grain flow units within the dune units. Hence a direct correlation between stratigraphy and band occurrence has been established that can be used to predict deformation band occurrences in similar sandstone reservoirs.