Elastic Properties Of Carbonate Rocks Research Articles

The influence of stress on the fracture and elastic properties of carbonate rocks controlled by strike-slip faults: a novel rock-physics modelling perspective

SUMMARY The fine-scale fractures within strike-slip faults substantially impact the flowing capacity. However, effective methods for their characterization are still lacking, making it challenging to predict hydrocarbon accumulation patterns. In this study, we conducted microscopic statistics, ultrasonic experiments and theoretical modelling to analyse the fracture density and elastic characteristics within the strike-slip fault and investigated the impact of stress. Our findings reveal that the fracture density in the fault core is 3–4 times higher than that in the damage zone, and the acoustic velocity is 13–18 per cent lower under atmospheric pressure. With the rising confining pressure, the fracture density initially decreases rapidly and then slowly, while the acoustic velocity follows the same increasing trend. The gradually slowing trend indicates that the majority of fractures close within the range of 0–20 MPa. Moreover, the stress sensitivity of the bulk modulus is higher than that of the shear modulus. The stress sensitivity is higher in the fault core than in the damage zone, which correlates strongly with the variation in fracture density. These indicate that the stress sensitivity in the fault-controlled rock is attributed to stress-induced fracture deformation, predominantly manifested as volumetric compression deformation. During the geological evolution, differences in tectonic faulting, fluid filling and compaction within the fault zone contribute to present heterogeneity in fracture density. Finally, our research demonstrates a strong correlation between theoretical prediction results and underground logging, drilling and core data. These findings can help predict the underground fracture distribution and elastic response of carbonate reservoirs controlled by strike-slip faults.

Effects of Regimes of Water Saturation on Static Elastic Properties of Carbonate Rocks

Effects of Regimes of Water Saturation on Static Elastic Properties of Carbonate Rocks

Investigating the analytical relationship between pore geometry and other pore space properties in carbonate rocks

Although pore geometry plays an important role in carbonate rock physics modelling, few studies have been carried out on its analytic relationship with other pore space properties such as pore space stiffness. We propose an analytical workflow based on the differential effective medium (DEM) to estimate the elastic properties of carbonate rocks. The validity of our results is then cross-checked with the Xu and Payne model on a real carbonate dataset. This workflow establishes a direct and quantitative link between the pore geometry of carbonate rock and its other pore space properties such as the Biot coefficient and pore space stiffness. This relationship can, furthermore, be utilized in defining rock physics templates (RPTs) to investigate the role of pore geometry on the rock elastic properties. Furthermore, we extended the Biot–Gassmann–Krief (BGK) model through our proposed workflow by establishing a theoretical framework to relate the main components of the BGK model to the pore geometry usually estimated in the laboratory or empirically. This can help to investigate the impact of fluid substitution on each of these main components. Our investigation suggests that the higher the Biot and Gassmann coefficients, the more sensitive the rock is to fluid substitution. Moreover, this analytical workflow has been employed to examine the role of selecting different rotational spheroids (i.e. oblate and prolate) on the modelled velocities. Our results show that the modelled velocities depend on this selection in such a way that prolate pores are less sensitive to the variations in their pore aspect ratio compared with oblate pores.

Linking elastic properties of various carbonate rocks to their microstructure by coupling nanoindentation and SEM-EDS

Characterizing the elastic properties of carbonate rocks is a crucial parameter in geotechnical and reservoir engineering. However, these natural materials exhibit a wide variety of microstructures, even when they belong to the same facies, leading to a significant dispersion of their elastic properties. We focus on six selected rocks, for which global porosity is shown to be not the only factor controlling elasticity. This study aims to understand which additional microstructural parameters impact the rocks’ elastic properties by means of nanoindentation coupled with microscopic observations and analyses. A complete procedure is developed to combine nanoindentation measurements with Scanning Electron Microscopy (SEM) - Energy Dispersive Spectroscopy (EDS) analyses to identify volume fractions and elastic properties of the mineral phases in each rock. The macroscopic Young’s moduli are estimated using analytical homogenization and are finally compared with the values obtained from macroscopic experiments. We find that the mineral composition and mechanical properties are critical parameters involved in carbonate rocks’ elastic behavior. However, while capturing the overall trend, homogenization is found to overestimate Young’s modulus. A discussion on the possible impact of cracks and non-spherical pores is conducted to explain this overestimation. Besides, microindentation tests are carried out to explore higher scales, which remain too small, however, to characterize the macroscopic Young’s modulus of carbonate rocks.

Impact of diagenesis and pore aspects on the petrophysical and elastic properties of carbonate rocks from southern Lebanon

Impact of diagenesis and pore aspects on the petrophysical and elastic properties of carbonate rocks from southern Lebanon

The heterogeneity of petrophysical and elastic properties in carbonate rocks controlled by strike-slip fault: A case study from yangjikan outcrop in the tarim basin

The petrophysical and elastic properties of the carbonate rocks controlled by strike-slip fault are still poor understood due to their significant complexities and strong heterogeneities, causing challenges for the exploitation and development of these carbonate reservoirs. To better comprehend the heterogeneity of petrophysical and elastic properties of the fault-controlled carbonate rocks, a small carbonate strike slip fault zone is selected, which is located in Yangjikan section in the Tarim basin. We combine the geostatistical, microscopic observation, petrophysical and ultrasonic analyses to characterize and understand the complexities and heterogeneity of petrophysical and elastic properties with different distance to the main fault core. The results show significant complexities and heterogeneities of petrophysical and elastic properties, and the variations of rocks drilled from the fault core are relatively drastic compared to those from the damage zone. The equivalent pore aspect ratios of the rocks are calculated from the differential effective medium theory, the values in the fault core are much higher compared to those from the damage zone, which can discriminate the pore network architectures and can represent reference for determination of the boundary of fractured damage zone. The controlling factors on the heterogeneity of the petrophysical and elastic properties for the selected fault zone are discussed, which mainly include the influence of fault structure position on fracture development, fluid selective filling on effective fracture and pore development, and the sequence on pore development. The results can contribute to the recognition and prediction of the petrophysical and elastic properties and hydrocarbon exploration in carbonate strike-slip fault zone in the Tarim Basin, and can provide reference for the construction of integrate multiscale heterogeneities models.

Determination of DynamicElastic Properties of Anah Formation, Near Rawa city / Western Iraq Using Ultrasonic Technique

The aim of the current study is to determine the elastic properties of carbonate rocks using ultrasonic method. Forty rock samples of Anah formation were collected at different depths from four wells drilled at the study area . The relationship between wave velocities and elastic properties of rocks was defined. Regression analyses to define these relations were applied. The results indicate that the elastic properties of the rocks show a linear relationship with both P- and S-wave velocities. The best relationship was obtained between both Young's modulus and Shear modulus with Vs in the determination of the coefficient ( R2 ), with values of 0.91 and 0.94, respectively. Bulk modulus and Lame’s constant were better correlated with Vp than with Vs in the determination of R2,with values of 0.92 and 0.83, respectively. Poisson’s ratio showed a good correlation using the ratio of Vp/Vs in the determination of R2, with a value of 0.81. The main output of this study shows that the ultrasonic method is a useful tool for the prediction of the elastic dynamic properties of sample rocks and that it can be used as an economical , simple and non- destructive method, especially for engineering purposes. 

Petrophysical and acoustic assessment of carbonate rocks, Zahle area, central Lebanon

Transport and acoustic measurements have been conducted on fifteen rock samples collected from central Lebanon to characterize the rock properties and to assess the impact of lithology, pore types, pore sizes, and textural parameters on the storage capacity and elastic characteristics. The spontaneous imbibition of selected samples was examined by detecting the moving capillary front across a sample. The coefficient of capillarity derived from the spontaneous imbibition is positively correlated with permeability. Seismic velocities in the studied rocks vary widely and are positively correlated with the rock density. Matrix-supported rocks with a larger proportion of micropores have lower seismic wave velocities, whereas the grain-supported carbonates exhibit low to moderate porosity and higher acoustic velocities. The elastic properties of the studied carbonates indicate a granular, rather than a crystalline, texture for the majority of the studied rocks. The widely variable elastic behavior of basically carbonate rocks implies that seismic reflection profiles in carbonate sequences may contain seismic reflections that do not result from non-carbonate intercalations but which result mainly from variable porosity, pore types, and shapes in the carbonate rocks themselves. This study provides important information on the textural, petrophysical, and elastic properties of carbonate rocks which are crucial for the assessment and understanding of the seismic reflection sections in subsurface carbonate reservoirs.

Bounds for Pore Space Parameters of Petroelastic Models of Carbonate Rocks

Abstract—This work is devoted to constructing parametric mathematical models of effective elastic properties of carbonate rocks based on the effective medium theory (petroelastic models). These models have recently been particularly in demand for exploration geophysics because they link the elastic properties of hydrocarbon reservoir rocks with the parameters of the void space—the shape and volume concentration of pores, cracks, and voids, and the degree of their connectivity. These parameters are determined from the measured velocities of elastic waves. However, the number of the unknown model parameters is, as a rule, larger than the number of the measured quantities so that such problems are underdetermined. In this case, the inverse problem of finding the model parameters may have an infinite number of solutions. Constraining the sought parameters with taking into account their physical meaning and existing experimental data can significantly increase the reliability of the obtained results and reduce the region of possible solutions of the inverse problem. In this work, we propose new approaches for constraining variations in the unknown model parameters which cannot be established from direct measurements, namely, for the connectivity of voids, crack porosity, and crack aspect ratio. Based on the correlation between the parameter of connectivity of voids and permeability, we developed an approach for constraining the range of variations in the parameter of connectivity of voids which relies on the Kozeny–Carman equation. The results of triaxial testing of rock samples on a servo hydraulic testing machine (press) are used for estimating the upper limit of crack porosity and assessing the crack shape. The characteristics of microstructure of the studied rocks obtained with the use of the established constraints increase the reliability of the constructed petroelastic models for carbonate rocks. These models can be subsequently used in various geophysical studies implying a relationship between the analyzed processes or properties and the microstructure of the rocks.

Predicting acoustic-wave velocities and fluid sensitivity to elastic properties in fractured carbonate formation

Estimation of S-wave velocity is one of the most critical steps for prestack seismic inversion. Based on the petrophysical model of fractured carbonate rocks, theoretical methods are firstly investigated for estimating P- and S-wave velocities in the presence of fractures. Then, the methods of calculating elastic properties in fractured carbonate rocks are discussed. The mineral concentration, total porosity, and fracture porosity from core X-ray diffraction and routine core measurements or log interpretation results are used to estimate the P- and S-wave velocities. In the given carbonate rock model, the elastic properties of carbonate rocks with different porosity and fractures are calculated. Two field tests prove that the proposed new method is effective and accurate. Furthermore, the model is useful for fluid identification, which is one of the most outstanding problems for carbonate reservoir description. The simulation results suggest that the larger the fracture porosity is, the easier fluid typing. In Tahe Oilfield, the elastic properties of different fluid zones indicate that bulk modulus and Young’s modulus are more sensitive to fluid than shear modulus, the Lamé constant, and Poisson’s ratio.

Simulation of elastic properties in carbonates

Predicting the elastic properties of carbonate rocks is crucial for the oil industry. However, the standard models that estimate effective elastic properties in porous media have many limitations in carbonate rocks. One main reason is highly complex pore-space structures, produced in carbonates by diagenesis and other geological processes, which create heterogeneities at several scales. Recently developed image acquisition systems, based on X-ray computed tomography, allow description of the spatial distribution of grains and pores in scanned samples at high resolution. Numerical simulations can then predict the elastic properties using the geometry of each phase (grains matrix and pore space). In this paper, we apply a new efficient automatic segmentation technique based on bi-level thresholding to separate grains and pores phases in 3D X-ray CT scans. Then we assess the ability of a finite-element simulation technique commonly used on sandstones to estimate the elastic properties of carbonate rocks under different fluid-saturation conditions.

Laboratory measurements of elastic properties of carbonate rocks during injection of reactive CO2-saturated water

[1] To investigate the coupled physical and chemical effects of injecting CO2-rich water into carbonate rock samples, we monitor the elastic and transport properties of six carbonate rocks, along with the calcium content and pH of the pore fluid under constant confining pressure. Carbonate samples range from calcite limestones containing dolomite to pure calcite mudstones, which allow us to study how mineral composition and microstructure affect the magnitude of the observed changes. The elastic properties of both the saturated and dry rock (i.e., rock frame) show a gradual loss of sstrength upon injection, as testified by the continuous decrease in the dry P- and S-wave velocity (and by proxy the bulk and shear moduli). The magnitude of the observed changes in the elastic properties varies among the samples, with a maximum relative change of 24.7% (871 m/s) and 21.2% (443 m/s) in P- and S- wave velocities, respectively. The decrease is also accompanied by a relative increase in permeability (up to 495%) and porosity (up to 19%). The observed changes likely derive from a change in microstructure, which is monitored over time via scanning electron microscopy. The variation in porosity results from two competing and interdependent processes: the chemical dissolution of calcite and the resulting mechanical compaction under pressure. The results of this study show that, upon injection of fluids that are in chemical disequilibrium with the hosting rock, the variation of the elastic properties cannot be described by existing rock-physics models.