What laboratory-induced dissolution trends tell us about natural diagenetic trends of carbonate rocks (original) (raw)
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Microstructures and physical properties in carbonate rocks: A comprehensive review
Marine and Petroleum Geology, 2019
Carbonate rocks are well-known to be tremendously heterogeneous. They mainly consist of component particles (from biological and non-biological origin) embedded in a lime-mud matrix and/or in a cement (composed of even smaller particles). The size, shape, density and spatial arrangement of those particles, alongside with natural fractures and cracks (although those are certainly not exclusive to carbonate rocks), define a microstructural pattern that is known to have a great influence on rock physical properties. Thus, to understand carbonate rock systems at large scales (formation, reservoir...), geophysicists have to study them at the pore scale, hoping to resolve the so-called "upscalling" problem. With this in mind, unravelling and identifying the relations between physical properties and carbonate rock microstructures is paramount for a global comprehension of a carbonate rock system. Since the late nineties, several research groups and authors have worked on documenting and providing significant insights into the microstructural parameters controlling the physical response of several rock properties (porosity, permeability, electrical conductivity, elastic, seismic and mechanical properties...) in carbonates. This article proposes a review of this specialized literature, from the early and recent contributions in rock physics, with emphasis on the recent studies on carbonate rocks from the Paris basin.
Sedimentary Geology, 2014
A dataset of 214 ultrasonic velocity and porosity measurements on Barremian-Aptian carbonates from Provence (SE France) provides well-constrained velocity-porosity transforms and allows the quantification of the impact of pore type and diagenetic history on these velocities. A numerical approach (EPAR: equivalent pore aspect ratio) was used to link diagenetic transformations, pore network evolution and elastic properties. Three categories of samples characterized by their dominant pore type were discriminated from the velocity and porosity database by means of the EPAR values derived from bulk (K-EPAR) and shear (μ-EPAR) moduli: 1) purely microporous limestones (low K-and μ-EPAR b 0.22), 2) samples with preserved intergranular and moldic pores (intermediate K-and μ-EPAR), and 3) vuggy limestones (K-and μ-EPAR N 0.3). Three velocity-porosity trajectories related to three diagenetic paths were defined and quantified from the Urgonian database: 1) EPARpreserving micro-scale cementation of micrite, 2) non-EPAR-preserving dissolution with moldic pore development and 3) EPAR-preserving sparry calcite cementation of molds. Equivalent Pore Aspect Ratio can therefore be regarded as a robust tool to decipher diagenetic trends in velocity-porosity transforms and may help predicting pore architecture from subsurface data.
Compaction and Failure in High Porosity Carbonates: Mechanical Data and Microstructural Observations
Pure and Applied Geophysics, 2009
We investigated systematically the micromechanics of compaction in two carbonates of porosity above 30%, Majella grainstone and Saint Maximin limestone. The composition, grain size and pore surface area of these rocks were determined. Hydrostatic compression experiments were performed under dry and wet conditions beyond the onset of grain crushing. A significant water weakening effect was observed in both rocks. A set of conventional triaxial experiments was also performed on both rocks under dry conditions at confining pressures ranging from 3 to 31 MPa. Microstructural observations were carried out on the deformed samples. The mechanical behavior of these high porosity carbonates is dominated by shear-enhanced compaction associated in most cases with strain hardening. Stress-induced cracking and grain crushing are the dominant micromechanisms of deformation in both rocks. In Majella grainstone, compactive shear bands appeared at low confinement, in qualitative agreement with the deformation bands observed in the field. At higher confining pressures, compaction localization was inhibited and homogeneous cataclastic flow developed. In Saint Maximin limestone, compaction localization was observed at all confining pressures. An increasing number of compactive shear bands at various orientations appeared with increasing strain. These new data suggest that compaction localization is important in the mechanical compaction of high porosity carbonates.
Effects of pore structure on velocity and permeability in carbonate rocks
Introduction 18 Methods 19 Image parameter-pore shape factor γ 28 Sensibility analysis of pore shape parameter γ 29 Correlation of γ and permeability 34 Variability of permeability and γ within a plug 38 Discussion: γ derived from OLM and ESEM 43 Conclusion 44 CHAPTER 2: ROLE OF MICRO-POROSITY FOR THE ACOUSTIC BEHAVIOR OF
Deformation bands in porous carbonate grainstones: Field and laboratory observations
Journal of Structural Geology, 2012
Recent field-based studies documented deformation bands in porous carbonates; these structures accommodate volumetric and/or shear strain by means of pore collapse, grain rotation and/or sliding. Microstructural observations of natural deformation bands in carbonates showed that, at advanced stages of deformation, pressure solution helps to reduce the grain size, enhancing comminuted flow and forming narrow cataclastic zones within the bands. In contrast, laboratory studies on the mechanics of deformation bands in limestones identified grain crushing, pore collapse and mechanical twinning as the micromechanisms leading to strain localization. Here, we present a multidisciplinary field and laboratory study performed on a Cretaceous carbonate grainstone to investigate the microprocesses associated to deformation banding in this rock. A quantitative microstructural analysis, carried out on natural deformation bands aimed at defining the spatial distribution of pressure solutions, was accompanied by a force chain orientation study. Two sets of triaxial experiments were performed under wet conditions on selected host rock samples. The deformed samples often displayed a shear-enhanced compaction behavior and strain hardening, associated with various patterns of strain localization. We constrained the pressure conditions at which natural deformation bands developed by reproducing in laboratory both low and high angle to the major principal stress axis deformation bands. The comparison among natural and laboratory-formed structures, allowed us to gain new insights into the role, and the relative predominance, of different microprocesses (i.e. microcracking, twinning and pressure solution) in nature and laboratory.
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.
Hydromechanical behavior of heterogeneous carbonate rock under proportional triaxial loadings
[1] The influence of stress paths representative of reservoir conditions on the poromechanical behavior and coupled directional permeabilities evolution of a heterogeneous carbonate has been studied. Our experimental methodology is based on performing confined compression tests keeping constant a stress path coefficient K = Ds r /Ds a ratio of the radial and axial stress magnitudes, commonly assumed to be representative of reservoir stress state evolution during production. The experiments are performed in a triaxial cell specially designed to measure the permeability in two orthogonal directions, along and transverse to the direction of maximum stress. The tested rock is a heterogeneous bioclastic carbonate, the Estaillades limestone, with a bimodal porosity, of mean value around 28% and a moderate permeability of mean value 125 mdarcy. Microstructural analyses of initial and deformed samples have been performed combining X‐ray tomography and microtomography, scanning electron microscopy (SEM) observations, and mercury injection porosimetry. The microstructural heterogeneity, observable by SEM, is characterized by the arrangement of the micrograins of calcite in either dense or microporous aggregates surrounded by larger pores. The spatial distribution of the two kinds of aggregates is responsible for important density fluctuations throughout the samples, recorded by X‐ray tomography, which characterizes the mesoheterogeneity. We show that this mesoheterogeneity is a source of a large directional variability of permeability for a given specimen and also from sample to sample. In addition, the fluctuation of the porosity in the tested set of samples, from 24% to 31%, is an expression of the macroheterogeneity. Macroscopic mechanical data and the stress path dependency of porosity and permeability have been measured in the elastic, brittle, and compaction regimes. No significant effect of the stress path on the evolution of directional permeabilities is observed in the elastic regime. At failure, according to the selected stress path, either a limited or a drastic permeability decrease takes place. From the postmortem observations at different scales, we clearly show the impact of the mesoheterogeneities on the localization of compaction, and we identify the precursor of the shear‐enhanced compaction and pore collapse mechanisms (for K ≥ 0.25) as an intense microcracking affecting only the denser aggregates. Applying an effective medium theory adapted to our observations, we propose a porosity scaling to normalize the pressures at failure. It is then found that the normalized critical pressures evolve linearly with the stress path coefficient. Consequently, we put forward a new definition of the yield cap for this type of carbonate, which is parameterized by the stress path coefficient. Citation: Dautriat, J., N. Gland, A. Dimanov, and J. Raphanel (2011), Hydromechanical behavior of heterogeneous carbonate rock under proportional triaxial loadings,
Depositional Facies, Pore Types and Elastic Properties of Deep-Water Gravity Flow Carbonates
Journal of Petroleum Geology, 2014
Quantitative petrographic analyses of deep-water resedimented carbonates from the Gargano Peninsula (SE Italy) were integrated with petrophysical laboratory measurements (porosity, Pand S-wave velocities) to assess the impact of sedimentary fabrics and pore space architecture on velocity-porosity transforms. Samples of Upper Cretaceous carbonate came from the Monte Sant'Angelo, Nevarra and Caramanica Formations and can be classified into four depositional facies associations: F1, lithoclastic breccias; F2, bioclastic packtones to grainstones; F3, interbedded grainstones-packstones and wackestones; and F4, (hemi-) pelagic mudstones. Five pore type classes were distinguished: I and II, dominant intercrystalline microporosity; IIIa, dominant intergranular macroporosity; IIIb, dominant mouldic macroporosity; and IIIc, mixed intergranular and mouldic macroporosity. Pore type was found to strongly control velocity-porosity transforms, unlike depositional facies associations.