Hydraulic Properties Of Rocks Research Articles

Analysis of the unsaturated hydraulic properties of rocks using multiple laboratory methods

Abstract Proper characterization of the unsaturated hydraulic properties in rocks is significant for predicting fluid flow in soil, hydrogeologic, and petroleum science and engineering problems. In this study, we contributed rigorous analysis of the unsaturated hydraulic properties of three reservoir rock samples (Berea Sandstone, Guelph Dolomite, and Indiana Limestone). An improved version of the standard evaporation method (HYPROP) was developed to cater specifically to rock samples. The improved HYPROP setup enables measurements of local water pressures within rock samples without disturbing the upper portion of the samples. The obtained results were compared with those obtained using the conventional pressure plate method and a state-of-the-art nuclear magnetic resonance (NMR) method. Observed data were analyzed in terms of four different unimodal and bimodal hydraulic functions. The HYPROP data were found to be relatively close to the pressure plate data of two carbonate rocks. The NMR-based data were reasonably consistent with the HYPROP data, with differences likely due in part to the fact that they were obtained using two different 5-cm long plugs taken from the same core. Heterogeneity along the rock cores from which the samples were taken could be a major reason for the observed differences, and hence should be considered in reservoir analyses.

Fluid-driven fault nucleation, rupture processes, and permeability evolution in oshima granite — Preliminary results and acoustic emission datasets

This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in fine-grained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data under different confining pressures for stress-driven fractures and under different water injection conditions for fluid-driven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process, 2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3) extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupture velocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEs changes from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershock activity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 ​m2/s to 10–100 ​m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating that hydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuring the safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparation process for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected to be used for various purposes, including 1) as training data for artificial intelligence related to microseismic data processing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models and assessment methods for the relationship between microseismic characteristics and rock hydraulic properties, which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.

Study on Hydrogeological Problems in Engineering Geological Investigation

Before the formal construction of buildings, it is necessary to carry out effective investigation on the engineering geology, hydrogeology and other contents in the construction area. Investigation is not only an important link for the project management personnel to carry out the project construction in the early stage, but also an important link to ensure the safety in the project construction process and the stability in the building construction process. Therefore, in order to effectively avoid various geological risks during the construction process or after the completion of the building, the early engineering geological survey is of great significance. In the process of engineering geological investigation, hydrogeological problems are also important investigation items. This paper will discuss and study hydrogeological problems, and propose effective measures for engineering geological exploration by analyzing the hydraulic properties of rock and soil mass and the impact of hydrogeological problems on the project.

Modeling unsaturated flow in fractured rocks with scaling relationships between hydraulic parameters

Modeling unsaturated flow in fractured rocks is essential in various subsurface engineering applications, but it remains a great challenge due to the difficulties in determining the unsaturated hydraulic properties of rocks that contain various scales of fractures. It is generally accepted that the van Genuchten (VG) model can be applied to fractured rocks, provided that the hydraulic parameters could be representatively determined. In this study, scaling relationships between the VG parameters ( α and n ) and hydraulic conductivity ( K ) across 8 orders of magnitude, from 10 −10 m/s to 10 −2 m/s, were proposed by statistical analysis of data obtained from 1416 soil samples. The correlations were then generalized to predict the upper bounds of VG parameters for fractured rocks from the K data that could be obtained more easily under field conditions, and were validated against a limited set of data from cores, fractures and fractured rocks available in the literature. The upper bound estimates significantly narrow the ranges of VG parameters, and the representative values of α and n for fractured rocks at the field scale can then be determined with confidence by inverse modeling using groundwater observations in saturated zones. The proposed methodology was applied to saturated-unsaturated flow modeling in the right-bank slope at the Baihetan dam site with a continuum approach, showing that most of the flow behaviors in fractured rocks in this complex hydrogeological condition could be properly reproduced. The proposed method overcomes difficulties in suction measurement in fractured rocks with strong heterogeneity, and provides a feasible way for modeling of saturated-unsaturated flow in fractured rocks with acceptable engineering accuracy.

Experimental investigation of the influence of carbonated water on sandstone and carbonate rock properties

Laboratory measurements using nuclear magnetic resonance, scanning electron microscopy, and gas porosity and permeability analysis were conducted to acquire a petrophysical interpretation of the Carbon Tan Sandstone and Savonnieres Carbonate for potential carbon dioxide storage in subsurface formations. The relationships between pore structures, such as pore-size distribution, pore geometry, and porosity/permeability, were investigated near and far from the wellbore. At operating pressures of 2500psi (17.24 MPa) and temperatures of 176 °F (50 °C), carbonated water was injected into a composite core constructed of two similar core samples bounded by a compact disc located between them. The current results showed that a strong calcite dissolution took place near the injection position of both rock samples and led to improvements in the primary intergranular permeability and porosity, while the carbonate sample showed significant improvement compared to sandstone. The durable heterogeneous dissolution of calcite grains also led to the creation of new pores as intra-granular micro-pores. While at deeper depths from the injection position, it noticed an insignificant development in pore structure and its populations as well as rock hydraulic properties of both rock samples. In conclusion, the study revealed that the injected carbonated brine had a valuable impact on fluid-formation interactive, which improved rock's inlet properties compared with outlet.

Geothermal reservoir characterisation of Devonian carbonates in North Rhine-Westphalia (W. Germany): Mineralogy- and depofacies-related extrapolation of petrophysical parameters

Across Germany, coal-fired power plants will be shut down not later than 2038. In the Rhine-Ruhr area of western Germany, their waste heat is the main supply for one of Europe’s largest district heating networks. Because of the projected shutdown of coal-fired power plants, sustainable alternatives must be implemented. This paper evaluates the hydrothermal potential of Devonian carbonates. A depofacies and mineralogy model is proposed and discussed. Tentative conclusions are drawn based on petrophysical laboratory tests. Extrapolating the thermal and hydraulic rock properties into geothermal reservoir depths offers constraints for associated reservoir simulations. This task applies existing and derived extrapolation equations taking local pressure and temperature gradients into consideration. The change from a non-linear to a linear development at the critical crack-closure pressure provides evidence regarding the petrophysical in-situ reservoir conditions. Results show a positive effect of increased dolomite volumes on reservoir properties. The spatial distribution of fracture networks significantly affects the geothermal reservoir potential, whereas the impact of regionally distributed depofacies variations is moderate. The critical crack-closure pressure equals 40MPa for limestones and 60MPa for dolomitic limestones, as well as dolostones, representing depths of approx. 3.6 and 5.4km, respectively. At depths of 6km, non-linear and linear extrapolation principles must be applied accordingly. At that depth, the thermal conductivity decreases by 14 to 20% compared to the outcrop values, depending on the sample category. The equivalent decrease in porosity amounts to one to two orders of magnitude. The permeability decrease equals three to four orders of magnitude. The petrophysical values of outcrop samples discussed here plot, within the error range, in the same domain as those of the Malm carbonates in the Munich area. Results are considered encouraging for those concerned with the sustainable transition of the district heating network in the Rhine-Ruhr area. Side-strands of regionally important fault systems, often characterised by hydrothermal dolomitisation, combine tectonic and petrophysical aspects that are advantageous and highly relevant for hydrothermal operations.

Dynamic SV‐Wave Signatures of Fluid‐Saturated Porous Rocks Containing Intersecting Fractures

AbstractDetecting fracture intersections is crucial for understanding rock hydraulic properties. For this purpose, we study the dynamic SV‐wave signatures of fluid‐saturated porous rocks containing intersecting fractures. A theoretical model is derived using the dynamic Biot's poroelasticity equations. Using this model, we analyze the features of SV‐waves and compare to those of previously studied P‐waves. The results show that the dispersion and attenuation of SV‐waves caused by elastic scattering and FF‐WIFF (Fracture‐Fracture Wave‐induced Fluid Flow) have a similar dependence on properties of intersecting fractures and fluid as those of P‐waves. However, the FB‐WIFF (Fracture‐Background Wave‐induced Fluid Flow) causes much smaller dispersion and attenuation for SV‐waves than for P‐waves. In particular, such dispersion and attenuation of SV‐waves are negligibly small for the orthogonally intersecting fractures regardless of wave incidence angles. In addition to the dispersion and attenuation, the WIFF and elastic scattering also greatly affect the anisotropy properties, which gives rise to frequency‐dependent velocity and attenuation anisotropies for both SV‐ and P‐ waves. Such anisotropy properties are sensitive to fracture intersection angles and are quite different between SV‐ and P‐ waves. These complementary features of SV‐ and P‐ waves provide the basis for fracture intersection detection using the combined features of these two waves. By comparing our model to the known results for the limiting cases, we validate our model.

Biotite supports long-range diffusive transport in dissolution–precipitation creep in halite through small porosity fluctuations

Abstract. Phyllosilicates are generally regarded to have a reinforcing effect on chemical compaction by dissolution–precipitation creep (DPC) and thereby influence the evolution of hydraulic rock properties relevant to groundwater resources and geological repositories as well as fossil fuel reservoirs. We conducted oedometric compaction experiments on layered NaCl–biotite samples to test this assumption. In particular, we aim to analyse slow chemical compaction processes in the presence of biotite on the grain scale and determine the effects of chemical and mechanical feedbacks. We used time-resolved (4-D) microtomographic data to capture the dynamic evolution of the porosity in layered NaCl–NaCl/biotite samples over 1619 and 1932 h of compaction. Percolation analysis in combination with advanced digital volume correlation techniques showed that biotite grains influence the dynamic evolution of porosity in the sample by promoting a reduction of porosity in their vicinity. However, the lack of preferential strain localisation around phyllosilicates and a homogeneous distribution of axial shortening across the sample suggests that the porosity reduction is not achieved by pore collapse but by the precipitation of NaCl sourced from outside the NaCl–biotite layer. Our observations invite a renewed discussion of the effect of phyllosilicates on DPC, with a particular emphasis on the length scales of the processes involved. We propose that, in our experiments, the diffusive transport processes invoked in classical theoretical models of DPC are complemented by chemo-mechanical feedbacks that arise on longer length scales. These feedbacks drive NaCl diffusion from the marginal pure NaCl layers into the central NaCl–biotite mixture over distances of several hundred micrometres and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983).

Comparison of cell- and vertex-centered finite-volume schemes for flow in fractured porous media

Flow in fractured porous media is of high relevance in a variety of geotechnical applications, given the fact that they ubiquitously occur in nature and that they can have a substantial impact on the hydraulic properties of rock. As a response to this, an active field of research has developed over the past decades, focusing on the development of mathematical models and numerical methods to describe and simulate the flow processes in fractured rock. In this work, we present a comparison of different finite volume-based numerical schemes for the simulation of flow in fractured porous media by means of numerical experiments. Two novel vertex-centered approaches are presented and compared to well-established numerical schemes in terms of convergence behavior and their performance on benchmark studies taken from the literature. The new schemes show to produce results that are in good agreement with those of established methods while leading to less degrees of freedom on unstructured simplex grids.

Measuring Fault Zone and Host Rock Hydraulic Properties Using Tidal Responses

AbstractPore pressure diffusion along faults influences induced seismicity and rupture mechanics. In situ hydraulic diffusivity measurements along faults are rare and generally lower than inferred from seismicity migration. Here we use the tidal response of deep geothermal boreholes to measure fault diffusivity and permeability. Initial interpretations of the observation with a homogeneous confined aquifer model result in diffusivities of 10−3–10−1 m2/s. However, this model mixes signals from both the conduit and the host rock. We develop a model for tidal response with a fault passing through the aquifer based on the fault‐guided fracture network and solve for hydraulic properties in both the fault and the host rock. The resulting fault permeability is 2 × 10−14–7 × 10−14 m2 (90% confidence interval[CI]) and fault diffusivity is 0.08–0.33 m2/s (90% CI), which is 2 orders of magnitude higher than the host rock diffusivity in some wells, thus highlighting the role of faults as fluid conduits.

Addressing nonlinear transient diffusion in porous media through transformations

The nonlinear differential equation describing flow of a constant compressibility liquid in a porous medium is examined in terms of the Kirchhoff and Cole-Hopf transformations. A quantitative measure of the applicability of representing flow by a slightly compressible liquid – which leads to a linear differential equation, the Theis equation – is identified. The classical Theis problem and the finite-well-radius problem in a system that is infinite in its areal extent are used as prototypes to address concepts discussed. This choice is dictated by the ubiquity of solutions that depend on these archetypal examples for examining transient diffusion. Notwithstanding that the Kirchhoff and Cole-Hopf transformations arrive at a linear differential equation, for the specific purposes of this work – the estimation of the hydraulic properties of rocks, the Kirchhoff transformation is much more advantageous in a number of ways; these are documented. Insights into the structure of the nonlinear solution are provided. The results of this work should prove useful in many contexts of mathematical physics though developed in the framework of applications pertaining to the earth sciences.

Petrophysical Correlations for the Permeability of Coquinas (Carbonate Rocks)

The pore structure of many carbonate formations is known to be very complex and heterogeneous. Heterogeneity is manifested by the presence of different types, sizes, and shapes of pores resulting from sedimentation and diagenetic actions. These complexities greatly increase uncertainties in estimated rock hydraulic properties in that different permeability values may occur for samples having similar porosities. In order to understand the effects of pore structure and heterogeneity, petrophysical analyses were performed on coquina samples from the Morro do Chaves Formation (Barremian, Sergipe-Alagoas Basin), which is an analogue of Brazilian Pre-salt oil reservoirs of Itapema Formation in the Santos Basin. Routine core analyses, and NMR and MICP measurements were carried out to obtain pore body and pore throat distributions. Obtained T2 relaxation times were converted to pore size radii by matching the NMR and MICP curves. Pore-scale imaging and pore network modelling were performed using microCT scans and the PoreFlow software, respectively. Calculated permeabilities using PoreFlow showed excellent agreement with the routine laboratory measurements. Samples having pore bodies with a higher coordination number showed much larger permeabilities at similar porosities. This study includes a statistical analysis of various features that caused the observed differences in permeability of the coquinas, including the role of connectivity of the entire porous system. Limitations and challenges of the various techniques, and the imaging and pore-scale flow simulations, are discussed.

Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny–Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.

Digital rock physics in four dimensions: simulating cementation and its effect on seismic velocity

SUMMARY Porosity exerts a strong control on the mechanical and hydraulic properties of rocks, but can often only be imaged indirectly from the surface using geophysical measurements, such as seismic velocity. Understanding and quantifying the relationship between seismic velocity and porosity is therefore a fundamental goal of many rock physics models. Simulating the geological processes that control porosity to generate digital rocks, and numerically modelling wave propagation to estimate their elastic properties, allows for flexible and rapid calibration of velocity–porosity trends. Here, the initial deposition of two digital carbonate sediments are simulated: grainstone (near spherical grains) and coquina (anisotropic shell fragments). The gradual precipitation of cement is then simulated, resulting in a suite of 3-D volumes of varying porosity with otherwise constant and known mineral and grain phases. These models are then used as input to a 3-D acoustic staggered-grid finite difference simulation of wavefield propagation, from which we estimate bulk seismic velocity and calculate the estimated bulk modulus. The resulting bulk modulus varies systematically with respect to porosity within the physical limits imposed by the Hashin–Shtrikman bounds. The samples exhibit anisotropy in the measured velocity consistent with structural anisotropy due to the settling of elongate grains under gravity. We use the resulting bulk velocity–porosity trends to test competing rock physics models, including one that accounts for varying effective pore-aspect ratio with porosity. The results validate the hypothesis that there is a power-law relationship between effective pore aspect ratio and porosity. This relationship is consistent with similar results obtained from a suite of natural carbonate grainstones examined in the laboratory. The results show the optimal rock physics model to be relatively insensitive to the degree of anisotropy in the fabric of the starting material, and may now be used with more confidence to link observed changes in effective pore aspect ratio to changes in porosity due to a range of geological processes, for example fracturing, dissolution and compaction, where other process-based models are available.

Pore Structure Changes Occur During CO2 Injection into Carbonate Reservoirs

Observations and modeling studies have shown that during CO2 injection into underground carbonate reservoirs, the dissolution of CO2 into formation water forms acidic brine, leading to fluid-rock interactions that can significantly impact the hydraulic properties of the host formation. However, the impacts of these interactions on the pore structure and macroscopic flow properties of host rock are poorly characterized both for the near-wellbore region and deeper into the reservoir. Little attention has been given to the influence of pressure drop from the near-wellbore region to reservoir body on disturbing the ionic equilibrium in the CO2-saturated brine and consequent mineral precipitation. In this paper, we present the results of a novel experimental procedure designed to address these issues in carbonate reservoirs. We injected CO2-saturated brine into a composite core made of two matching grainstone carbonate core plugs with a tight disk placed between them to create a pressure profile of around 250 psi resembling that prevailing in reservoirs during CO2 injection. We investigated the impacts of fluid-rock interactions at pore and continuum scale using medical X-ray CT, nuclear magnetic resonance, and scanning electron microscopy. We found that strong calcite dissolution occurs near to the injection point, which leads to an increase in primary intergranular porosity and permeability of the near injection region, and ultimately to wormhole formation. The strong heterogeneous dissolution of calcite grains leads to the formation of intra-granular micro-pores. At later stages of the dissolution, the internal regions of ooids become accessible to the carbonated brine, leading to the formation of moldic porosity. At distances far from the injection point, we observed minimal or no change in pore structure, pore roughness, pore populations, and rock hydraulic properties. The pressure drop of 250 psi slightly disturbed the chemical equilibrium of the system, which led to minor precipitation of sub-micron sized calcite crystals but due to the large pore throats of the rock, these deposits had no measurable impact on rock permeability. The trial illustrates that the new procedure is valuable for investigating fluid-rock interactions by reproducing the geochemical consequences of relatively steep pore pressure gradients during CO2 injection.

Mudstone redox conditions at the Horonobe Underground Research Laboratory, Hokkaido, Japan: Effects of drift excavation

The mechanical and hydraulic properties of rocks around mine drifts change significantly during the construction and operation of a radioactive-waste repository, with air intrusion typically causing the oxidation of rock and groundwater in excavation-damaged zones (EDZ). Redox conditions in such zones associated with niches excavated in mudstone at the Horonobe Underground Research Laboratory (URL), which is believed to be generally representative of conditions that could exist in the EDZ of a repository, were studied with the aim of improving our understanding of factors that control redox conditions in such rock–groundwater systems. Groundwater Eh values around the niches have reducing values of less than −150 mV. The SO42− concentration, regarded as an oxidation indicator, is consistently as low as 1 μmol L−1. Gas occupies >50% of zone volumes, including CH4 and CO2 with traces of N2 and O2. Cores drilled from host rock around a URL gallery were analyzed, with no pyrite dissolution or precipitation of calcium sulfates being found. It is concluded that oxidizing conditions do not exist in the excavation-damaged zones, which is attributed to the suppression of air intrusion by the release of CH4 and CO2 from groundwater as pressures decreased and their accumulation in fractures. The modeling of oxygen diffusion into host rock further indicates that a reducing environment is maintained around the URL drifts.

Numerical calculation and multi-factor analysis of slurry diffusion in an inclined geological fracture

Slurry grouting plays an important role in water plugging for hydrogeological engineering and there are multiple factors that restrict the slurry flow. This study investigates the restriction mechanisms, based on a single inclined rough fracture, employing a space stepwise method (SSM) using multi-direction sectors (MDS) for calculating the diffusion of variable-viscosity slurry under constant flow. The specifically developed numerical algorithm is validated by experimental results. The spatio-temporal effects of major factors on the flow, and the rock hydraulic properties, were analyzed for cement-based slurry. The results show that the slurry flow calculated by MDS-SSM exhibits strong fitting with experimental results. The diffusion pattern no longer exhibits a circular plane, but rather a double semi-elliptical distribution. The fracture direction angle, especially for the upward vertical flow, must be considered in the case of a larger dip angle. The main controlling factor of the pressure field is the higher slurry viscosity in regions far from the injection hole, and the influence of dip angle is significantly greater closer to the hole. Roughness has an influence on the fracture hydraulic properties, and the required grouting pressure increases with an increase in roughness. The fracture aperture, viscosity coefficient, and diffusion radius are three key factors with strong sensitivity affecting the forecasting accuracy of grouting parameters. The role of the fracture dip angle can be neglected only in narrow fractures and long-distance diffusion with higher-viscosity slurry or larger pressure. The key threshold value can be obtained with a fitting formula under given conditions.

Correlation of near surface fractures with seismic radial anisotropy: An approach for near surface fracture identification

Fluid flow and solute transport in geologic environments are vital for natural systems, public well-being, and infrastructure that rely on understanding subsurface hydrology. Fractures strongly affect the hydraulic properties of rocks as they often serve as preferential flow paths for fluids. Therefore, the characterization of subsurface fractures is crucial to understand fluid flow in the geological environments and estimate the hydraulic properties of fractured-rock formations. Seismic radial anisotropy that is defined with respect to the difference between the velocity of a vertically polarized S-wave (SV) and one polarized horizontally (SH) can be used as a strong attribute for forecasting near surface fractures. We evaluate the correlation of seismic radial anisotropy with near-surface fractures. We obtain seismic radial anisotropy models at two sites with different bedrock geologies (one metamorphic-igneous and the other sedimentary) using dispersion analyses of the Rayleigh waves, for vertical polarization, and Love waves, for horizontal polarization. The seismic radial anisotropies at these two sites show a strong correlation with near surface fractures. We also perform a sensitivity analysis to obtain an optimum cut-off value to better interpret seismic radial anisotropy in terms of fracture probability.

Fast 4‐D Imaging of Fluid Flow in Rock by High‐Speed Neutron Tomography

AbstractHigh‐speed neutron tomographies (1‐min acquisition) have been acquired during water invasion into air‐filled samples of both intact and deformed (ex situ) Vosges sandstone. Three‐dimensional volume images have been processed to detect and track the evolution of the waterfront and to calculate full‐field measurement of its speed of advance. The flow process correlates well with known rock properties and is especially sensitive to the distribution of the altered properties associated with observed localized deformation, which is independently characterized by Digital Volume Correlation of X‐ray tomographies acquired before and after the mechanical test. The successful results presented herein open the possibility of in situ analysis of the local evolution of hydraulic properties of rocks due to mechanical deformation.

Estimation of the Non‐Darcy Coefficient Using Supercritical CO2 and Various Sandstones

AbstractNon‐Darcy flow (also known as high‐velocity flow, inertial flow, etc.) often occurs in the near‐well region of a reservoir during injection or production. This flow needs to be characterized and its origins fully understood, as it is a critical factor in reducing well productivity. The Forchheimer equation, which describes fluid flow considering an inertial effect, can be adopted to analyze non‐Darcy flow. In particular, the non‐Darcy coefficient in the equation represents inertial resistance in a porous medium and is an empirical value that depends on the pore geometry and fluid properties. This study, as part of research on geological CO2 storage, reports non‐Darcy flow tests with a high flow rate and examines the non‐Darcy coefficient by using supercritical CO2 and various sandstones. The dependence of the coefficient on the properties of the supercritical CO2 was also assessed in a series of non‐Darcy tests under different pore pressures. The coefficient varied with the properties of the supercritical CO2 and sandstone. As the permeability of sandstone increased, the non‐Darcy coefficient decreased nonlinearly and converged to a value. The results also indicate that the coefficient is reduced with a decreasing ratio of density to viscosity for the supercritical CO2. An equation predicting the coefficient was derived, having the advantage that both the hydraulic properties of rock and the fluid properties can be considered simultaneously in a dimensionally correct analysis.