Deformation Of Sedimentary Rocks Research Articles

Anisotropic continuum framework of coupled gas flow – adsorption – deformation in sedimentary rocks

AbstractSolid deformation is always a crucial factor of gas transport in sedimentary rocks. While previous studies always adopt the assumption of isotropic poroelastic deformation, anisotropic poroelastoplastic deformation is rarely considered, despite anisotropy being a ubiquitous property of natural sedimentary rocks. In this work, an anisotropic poromechanical model is established to analyze the matrix porosity and apparent permeability evolutions during the process of gas migration. Using a thermodynamic formulation that treats the fluid–solid interface as an independent phase, we derive a rate form for matrix porosity and obtain the new dissipation function that contains three parts: dissipations from solid deformation, gas adsorption, and fluid flow. For gas adsorption, we justify the rationality of the adopted model; for fluid flow, the updated porosity can be substituted into sophisticated apparent permeability models for full‐scale analysis; and for solid deformation, a recently developed constitutive model appropriate for rocks exhibiting transverse isotropy in both the elastic and plastic responses is adopted in this work. Through the novel stress‐point simulation incorporating two effective stress measures and adsorption strain, new patterns of apparent permeability are obtained, which fit the experimental data quite well and cannot be reproduced from the assumption of isotropic poroelasticity. The advantages of our poromechanical model include thermodynamic consistency and the ability to employ finite‐element‐based formulation. Finally, an initial‐boundary value problem of gas production considering anisotropic plasticity is conducted, and the effects of the bedding plane and different adsorption models are highlighted.

Petroleum system analysis and thermal evolution of the deepwater NW Borneo fold-thrust belt

The generation of hydrocarbons in source rocks can lead to overpressure, which can support development of detachments and the deformation of sedimentary rocks. In turn, the deformation of rock units by e.g., large-scale overthrusting can lead to tectonic-driven burial. Tectonic-driven burial can generate overpressure, which in turn can influence the petroleum system. In fold-thrust belts, an integrated understanding of both, the tectonic and the petroleum systems is important for understanding the potentially complex interaction of faulting, folding and fluid geochemistry. This study combines structural restoration and basin-modeling techniques to provide a comprehensive view of the fold-thrust system offshore northwest Borneo.In the deepwater region offshore northwest Borneo a major fold-thrust belt is present. The thrust belt is characterized by a mix of gravity-driven folding and faulting in a southwestern domain, and deep-seated crustal deformation in a northeastern domain. Oil and gas preferentially accumulated in thrust-top anticlines. The NW Borneo fold-thrust belt has a low taper angle; likely related to fluid overpressure along the basal detachment. The basin models presented in this study are based on an integration of regional 3D seismic-reflection interpretation, borehole analysis and 2D kinematic restoration. 2D petroleum systems modeling shows oil and gas generation and expulsion from Middle Miocene coaly source rocks since the Late Miocene, migration of the hydrocarbons through carrier beds and faults, and the accumulation of oil and gas in thrust-hangingwall anticlines. Vertical gas leaks modeled are comparable with gas clouds observed on 3D seismic-reflection data. The risk of biodegradation was estimated for reservoirs shallower than 1000–1500 m, and their burial is influenced by uplift due to thrusting. Combined tectonic and thermal modeling of the fold-thrust belt indicates the initiation of shortening at the time when the maturation of the source rock at the basal detachment was within the oil window. The timing of the maximum shortening rate, however, exhibits regional variations across the fold-thrust belt. In the gravity-driven fold thrust system in the southwest, the primary control on the peak of shortening is the maturation of the source rock at basal detachment level (gas window). In contrast, the peak of shortening in the northeast with the deep-seated crustal-driven system is interpreted as being primarily controled by the intensity and timing of the external stress.

Fold–Thrust Deformations of New Siberia Island (Novosibirsky Islands, Russia): Age, Morphology, and Genesis of Structures

Detailed lithological, stratigraphic, and structural studies of the fold-thrust structures were conducted on New Siberia Island. We have established that the jointly deformed complexes of the Upper Cretaceous–Middle Neopleistocene are overlapped by undeformed sediments of the Upper Neopleistocene. This fact confirms the completion of the deformation process at the end of the Middle Neopleistocene. An additional argument excluding the ancient age of dislocations is the result of the fission track dating for apatites. The resulting track ages of apatites significantly exceeded the age of deformed rocks, which was reliably established by the other methods. In deformed complexes, unlithified permafrost rocks predominate. Folded structures are characterized by joint deformation of sedimentary rocks, formation ice and ice-ground, inconsistency of fold orientation and different direction of structural evolution in the northern and southern parts of the island New Siberia. Considering the correspondence of the established age of dislocations to the age of the largest Pleistocene glaciation, all these facts allow us to state that the fold-and-thrust deformations of the island New Siberia are glaciodislocations.

Cretaceous intracontinental rifting and post-rift inversion in NE Brazil: Insights from the Rio do Peixe Basin

The breakup of Pangea in the Mesozoic placed the South American and African plates under horizontal extension, which triggered rifting and the formation of intracontinental basins in NE Brazil. The subsequent geodynamic evolution changed the forces acting upon the South American plate because of the simultaneous development of the Mid-Atlantic Ridge (MAR) and the Andes. The problem we address in this work is the effect of the changing stress field on intracontinental deformation in NE Brazil, and we used the intracontinental Rio do Peixe Basin (RPB) as case study. We used remote sensing, shuttle radar topography, geophysical data, and detailed structural geology to address this problem. Based on the integrated analysis of brittle deformation within the basin, at the basin boundaries, and in the host basement, we conclude the following: (1) In the Cretaceous, the Rio do Peixe Basin formed from an approximately NW–SE tension, as deduced from brittle deformation in sedimentary rocks within the RPB and bounding master faults. (2) Subsequently, the maximum compressive stress that acted upon the study area shifted from vertical to horizontal, and was oriented approximately ENE–WSW. The new compressive stress field inverted the RPB, which is recorded in the basin at all scales. (3) The inversion of the RPB is consistent with the stress field imposed by the MAR push (to the west) and the Andean push (to the east), which have kept the South American plate under ENE–WSW horizontal compression since the late Cretaceous.

Transition from extensional to compressional magnetic fabrics in the Cretaceous Cabuérniga basin (North Spain)

The transition between extensional and compressional-driven magnetic fabrics in sedimentary rocks is explored in this paper through the study of an example of the Basque–Cantabrian basin. In the area where extensional structures prevail and no superimposed deformation is observed, except for gentle large-scale folds, the magnetic fabric is interpreted as extensional, in consistency with mesostructural (tension gashes) and macrostructural (large-scale faults) data. Compressional tectonic fabrics are unequivocally interpreted in the area with cleavage development related to the buttressing of the syn-rift sequence against faults located near the northern basin margin. In this area, kmax is oriented according either to the intersection lineation or the dip direction of cleavage planes. In the area located in-between, where no macroscopic evidence of either compression or extension exist, there is a transitional fabric between compressional (resulting from the modification during inversion of a previous sedimentary or extensional fabric) and extensional (inherited from the extensional stage) magnetic fabrics that correlate with subtle evidences at the microscopic scale (pressure shadows, deformation and re-orientation of nodules). Therefore, the magnetic fabric is revealed as an exceptionally sensitive marker of deformation in sedimentary rocks. This transition in the magnetic fabric occurs within a length of 6.25 km along the cross-section that correlates with a thickness of 200 m of the stratigraphic pile. These results indicate that even in the absence of clear structural markers of compressional deformation, extensional magnetic fabrics can be only interpreted when there is a minimum separation (in the vertical or the horizontal) to the cleavage front.

Kilometer-scale chemical reaction boundary patterns and deformation in sedimentary rocks

We use three-dimensional (3D) seismic data to image patterns developed by kilometer-scale chemical reaction boundaries to demonstrate that chemical patterns are scaleable phenomena. The patterns develop in biosiliceous marine successions due to the dissolution of opal-A (biogenic silica) and reprecipitation as opal-CT (Crystobalite and Tridymite) during burial. The reaction boundary patterns comprise roughly circular regions where the reaction boundary has preferentially advanced. These regions are up to 2.7 km wide, and c. 50–200 m in height and are termed cells. The cells form by amalgamation with adjacent juvenile cells. They also form by the incorporation of much smaller regions surrounding the cells where the chemical change has already occurred that we term ‘satellites’ (50 m wide). The reaction results in enhanced rates of sediment compaction hence differential advancement of reaction boundaries causes differential subsidence of the overburden, inducing folding and faulting of the overburden above the cellular promontories. We propose three potential mechanisms for the development of kilometer-scale reaction boundary patterns: (a) mass transport of silica by advection (b) perturbation of isotherms as a result of convective or conductive heat transport or (c) establishment of a positive feedback loop between fluid production due to the reaction, hydraulic fracturing and the upward and lateral transport of fluids. This study provides the first insights into how strongly patterned diagenetic reaction boundaries evolve at a basin scale, an initial conceptualization of the potential range of reaction boundary morphologies that could exist in this diagenetic system, and the likely mechanisms that could control them. Furthermore it demonstrates that the discipline of ‘seismic diagenesis’ could represent a completely new approach for the study of chemical diagenetic processes in sedimentary rocks.

Growth of stylolite teeth patterns depending on normal stress and finite compaction

Stylolites are spectacular rough dissolution surfaces that are found in many rock types. They are formed during a slow irreversible deformation in sedimentary rocks and therefore participate to the dissipation of tectonic stresses in the Earth's upper crust. Despite many studies, their genesis is still debated, particularly the time scales of their formation and the relationship between this time and their morphology. We developed a new discrete simulation technique to explore the dynamic growth of the stylolite roughness, starting from an initially flat dissolution surface. We demonstrate that the typical steep stylolite teeth geometry can accurately be modelled and reproduce natural patterns. The growth of the roughness takes place in two successive time regimes: i) an initial non-linear increase in roughness amplitude that follows a power-law in time up to ii) a critical time where the roughness amplitude saturates and stays constant. We also find two different spatial scaling regimes. At small spatial scales, surface energy is dominant and the growth of the roughness amplitude follows a power-law in time with an exponent of 0.5 and reaches an early saturation. Conversely, at large spatial scales, elastic energy is dominant and the growth follows a power-law in time with an exponent of 0.8. In this elastic regime, the roughness does not saturate within the given simulation time. Our findings show that a stylolite's roughness amplitude only captures a very small part of the actual compaction that a rock experienced. Moreover the memory of the compaction history may be lost once the roughness growth saturates. We also show that the stylolite teeth geometry tracks the main compressive stress direction. If we rotate the external main compressive stress direction, the teeth are always tracking the new direction. Finally, we present a model that explains why teeth geometries form and grow non-linearly with time, why they are relatively stable and why their geometry is strongly deterministic while their location is random.

Orogen‐scale decollements

The continental lithosphere responds to stress by deforming as a generally layered medium. Deep seismic reflection data, coupled with a variety of ancillary geological and geophysical data, are interpreted to provide images of fault zones that tend to form moderately dipping ramp structures in mechanically rigid layers, and flat detachments in mechanically weak layers. This geometry is similar to ramp and flat structures observed at smaller scales in thrust and fold belts and leads to the interpretation that most orogens are underlain by orogen‐scale décollements in a manner that is analogous to so‐called “thin skin” deformation in sedimentary rocks. Décollements may occur within the crust (for example, near the base of a sedimentary section or in the middle crust), near the Moho, in the subcrustal lithosphere, or in the asthenosphere. Even intracratonic basement‐cored (“thick skin”) uplifts that occasionally occur in foreland regions such as the Wyoming province are probably large (crustal) scale versions of ramp/flat features observed in supracrustal rocks and are thus likely caused by the same fundamental tectonic processes.

On the detection of weak strain parallel to the bedding by magnetic anisotropy: A mathematical model study

Five mathematical models of the superposition of deformational magnetic fabric on sedimentary magnetic fabric are presented. These models are represented by various combinations of pure shear and simple shear. The diagrams of the variations in the main magnetic anisotropy parameters with strain can help in recognizing weak ductile deformation in sedimentary rocks.

Effect of geological compaction on the deformation of sedimentary rocks : Koide, H; Hoshino, K; Endo, G Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 1, P211–214. Publ Rotterdam, A A Balkema, 1979

Effect of geological compaction on the deformation of sedimentary rocks : Koide, H; Hoshino, K; Endo, G Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 1, P211–214. Publ Rotterdam, A A Balkema, 1979

A geochemical investigation of pressure solution and the formation of veins in a deformed greywacke

Pressure solution and vein formation often occur simultaneously in shear zones during the deformation of sedimentary rocks. The mineralogical and chemical variations around a typical example of an en echelon zone of quartz veins from north Cornwall are discussed in detail. Solution of quartz is confined to the shear zone and occurs along discrete surfaces. Accumulation of insoluble minerals along these surfaces gives rise to spaced pressure solution cleavage. Petrographic data show that during pressure solution the breakdown of felspar and epidote results in the crystallisation of clay mineral, quartz and siderite. Redistribution of silica within the shear zone by pressure solution does not account for all the quartz in the veins, or for the observed increased concentration of iron and calcium. It is concluded that material was introduced from an external source into the shear zone.

Genetic and Geometric Relations Between Structures in Basement and Overlying Sedimentary Rocks, with Examples from Colorado Plateau and Wyoming

Field studies of jointing, faulting, and folding in the San Juan-Grand Canyon region, Arizona, and the Big Horn Mountains-North Laramie range, Wyoming, show that tectonic movements are primarily vertical. Maximum deformation of the rocks occurs along narrow, linear zones which appear to follow elements of a primordial fracture pattern in the Precambrian basement. Sedimentary rocks play a passive role in the formation of folds and structural lineaments. Fold geometries are determined by the developing geometry of the basement surface. The basic causes and mechanisms of deformation are generated in basement rocks below the level of the sedimentary strata. Structures in the sedimentary strata are of secondary origin, generated as a result of folding following basement deformation. Prominent fracture trends of Precambrian age in the basement rocks of the Grand Canyon region are present as major elements of the joint patterns in overlying sedimentary rocks. Large-order structural lineaments in the Big Horn Mountains region are long, narrow zones of deformation in sedimentary rocks which reflect deformations in the underlying basement rocks. Areally, structural lineaments follow some element of the regional fracture pattern.