Evolution of Fracture Aperture in Quartz Sandstone under Hydrothermal Conditions: Mechanical and Chemical Effects

Fractures efficiently affect fluid flow in geological formations, and thereby determine mass and energy transport in reservoirs, which are not least exploited for economic resources. In this context, their response to mechanical and thermal changes, as well as fluid–rock interactions, is of paramount importance. In this study, a two-stage flow-through experiment was conducted on a pure quartz sandstone core of low matrix permeability, containing one single macroscopic tensile fracture. In the first short-term stage, the effects of mechanical and hydraulic aperture on pressure and temperature cycles were investigated. The purpose of the subsequent intermittent-flow long-term (140 days) stage was to constrain the evolution of the geometrical and hydraulic fracture properties resulting from pressure solution. Deionized water was used as the pore fluid, and permeability, as well as the effluent Si concentrations, were systematically measured. Overall, hydraulic aperture was shown to be significantly less affected by pressure, temperature and time, in comparison to mechanical aperture. During the long-term part of the experiment at 140 °C, the effluent Si concentrations likely reached a chemical equilibrium state within less than 8 days of stagnant flow, and exceeded the corresponding hydrostatic quartz solubility at this temperature. This implies that the pressure solution was active at the contacting fracture asperities, both at 140 °C and after cooling to 33 °C. The higher temperature yielded a higher dissolution rate and, consequently, a faster attainment of chemical equilibrium within the contact fluid. X-ray µCT observations evidenced a noticeable increase in fracture contact area ratio, which, in combination with theoretical considerations, implies a significant decrease in mechanical aperture. In contrast, the sample permeability, and thus the hydraulic fracture aperture, virtually did not vary. In conclusion, pressure solution-induced fracture aperture changes are affected by the degree of time-dependent variations in pore fluid composition. In contrast to the present case of a quasi-closed system with mostly stagnant flow, in an open system with continuous once-through fluid flow, the activity of the pressure solution may be amplified due to the persistent fluid-chemical nonequilibrium state, thus possibly enhancing aperture and fracture permeability changes.

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Effects of pore fluid flow and chemistry on compaction creep of calcite by pressure solution at 150°C

Geofluids ◽

10.1111/j.1468-8123.2010.00323.x ◽

2011 ◽

Vol 11 (1) ◽

pp. 108-122 ◽

Cited By ~ 11

Author(s):

X. ZHANG ◽

C. J. SPIERS ◽

C. J. PEACH

Keyword(s):

Fluid Flow ◽

Pore Fluid ◽

Pressure Solution

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Numerical Research of Fluid Flow and Solute Transport in Rough Fractures under Different Normal Stress

Geofluids ◽

10.1155/2020/8845216 ◽

2020 ◽

Vol 2020 ◽

pp. 1-17

Author(s):

Min Wang ◽

Qifeng Guo ◽

Pengfei Shan ◽

Meifeng Cai ◽

Fenhua Ren ◽

...

Keyword(s):

Fluid Flow ◽

Shear Flow ◽

Solute Transport ◽

Normal Stress ◽

Three Dimensional ◽

Dispersive Transport ◽

Mean Velocity ◽

Flow Test ◽

Hydraulic Aperture ◽

Mechanical Aperture

The effects of roughness and normal stress on hydraulic properties of fractures are significant during the coupled shear flow test. Knowing the laws of fluid flow and solute transport in fractures is essential to ensure the nature and safety of geological projects. Although many experiments and numerical simulations of coupled shear flow test have been conducted, there is still a lack of research on using the full Navier-Stokes (N-S) equation to solve the real flow characteristics of fluid in three-dimensional rough fractures. The main purpose of this paper is to study the influence of roughness and normal stress on the fluid flow and solute transport through fractures under the constant normal stiffness boundary condition. Based on the corrected successive random addition (SRA) algorithm, fracture surfaces with different roughness expressed by the Hurst coefficient ( H ) were generated. By applying a shear displacement of 5 mm, the sheared fracture models with normal stresses of 1 MPa, 3 MPa, and 5 MPa were obtained, respectively. The hydraulic characteristics of three-dimensional fractures were analyzed by solving the full N-S equation. The particle tracking method was employed to obtain the breakthrough curves based on the calculated flow field. The numerical method was verified with experimental results. It has been found that, for the same normal stress, the smaller the fracture H value is (i.e., more tough the fracture is), the larger the mechanical aperture is. The ratio of hydraulic aperture to mechanical aperture ( e h / e m ) decreases with the increasing of normal stress. The smaller the H value, the effect of the normal stress on the ratio e h / e m is more significant. The variation of transmissivity of fractures with the flow rate exhibits similar manner with that of e h / e m . With the normal stress and H value increasing, the mean velocity of particles becomes higher and more particles move to the outlet boundary. The dispersive transport behavior becomes obvious when normal stress is larger.

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Shear-Thinning Fluid Flow in Variable-Aperture Channels

Proceedings ◽

10.3390/ecws-4-06426 ◽

2019 ◽

Vol 48 (1) ◽

pp. 28

Author(s):

Alessandro Lenci ◽

Vittorio Di Federico

Keyword(s):

Fluid Flow ◽

Pressure Gradient ◽

Flow Rate ◽

Geometric Model ◽

Shear Thinning ◽

Single Fracture ◽

Fracture Aperture ◽

Nonlinear Phenomenon ◽

Hydraulic Aperture ◽

Fluid Rheology

Non-Newtonian fluid flow in a single fracture is a 3D nonlinear phenomenon that is often averaged across the fracture aperture and described as 2D. To capture key interactions between fluid rheology and spatial heterogeneity, we adopted a simplified geometric model to describe aperture variability, consisting of adjacent one-dimensional channels with constant aperture, each drawn from assigned aperture distribution. The flow rate was then derived under the lubrication approximation for the two limiting cases of an external pressure gradient that was parallel/perpendicular to the channels; these two arrangements provided an upper/lower bound to fracture conductance. Fluid rheology was described via the Prandtl–Eyring shear-thinning model. Novel closed-form results for flow rate and hydraulic aperture were derived and are discussed; different combinations of parameters describing the fluid rheology and variability of the aperture field were considered. In general, flow rate depends, in a nonlinear fashion, on the dimensionless pressure gradient and distribution parameters.

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Intrinsic anisotropy in fracture permeability

Interpretation ◽

10.1190/int-2014-0230.1 ◽

2015 ◽

Vol 3 (3) ◽

pp. ST43-ST53 ◽

Cited By ~ 3

Author(s):

Mehdi Mokhtari ◽

Azra N. Tutuncu ◽

Gregory N. Boitnott

Keyword(s):

Fluid Dynamics ◽

Fluid Flow ◽

Hydraulic Fracture ◽

Numerical Data ◽

Fracture Aperture ◽

Fracture Permeability ◽

Fracture Geometry ◽

Mechanical Fracture ◽

Proppant Transport ◽

Intrinsic Anisotropy

Contrary to the assumption in cubic law, the surface of fractures has some degree of roughness, which impacts their fluid dynamics. Incorporating the effect of roughness can improve the simulation of fluid flow in fractures and faults, as well as proppant transport in hydraulic fracturing. To investigate the effect of roughness on the fluid flow, we created a fracture using the Brazilian test, and its roughness was measured using a laser profilometer. Experimental permeability measurements showed a reduction in permeability as the effective stress increased. However, the unmatching surfaces of the fracture prevented its complete mechanical closure. Numerical simulations of the fluid dynamics were conducted on the measured fracture geometry. We determined that the hydraulic fracture aperture is less than the mechanical fracture aperture and that there was anisotropy in the fracture permeability. The ratio of hydraulic fracture aperture to mechanical fracture aperture, as well as anisotropy in fracture permeability, increased when the fracture aperture decreased. The anisotropy in fracture permeability was 45% at the lowest simulated fracture aperture. Integrating the experimental and numerical data, we estimated the fracture porosity and fracture permeability.

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Mechanical-Chemical-Mineralogical Controls on Permeability Evolution of Shale Fractures

Geofluids ◽

10.1155/2018/7801843 ◽

2018 ◽

Vol 2018 ◽

pp. 1-18 ◽

Cited By ~ 1

Author(s):

Yunzhong Jia ◽

Yiyu Lu ◽

Jiren Tang ◽

Yi Fang ◽

Binwei Xia ◽

...

Keyword(s):

Fracture Surface ◽

Clay Mineral ◽

Chemical Constituents ◽

Gas Production ◽

Pressure Solution ◽

Fracture Aperture ◽

Permeability Evolution ◽

Fracture Permeability ◽

Free Face ◽

Hydraulic Aperture

We report experimental observations of permeation of CO2-rich aqueous fluids of varied acidic potential (pH) on three different shales to investigate mechanical, chemical, and mineralogical effects on fracture permeability evolution. Surface profilometry and SEM-EDS (scanning electron microscopy with energy-dispersive X-ray spectroscopy) methods are employed to quantify the evolution in both roughness on and chemical constituents within the fracture surface. Results indicate that, after 12 hours of fluid flow, fracture effective hydraulic apertures evolve distinctly under different combinations of shale mineralogy, effective stress, and fluid acidity. The evolution of roughness and transformation of chemical elements on the fracture surface are in accordance with the evolution of permeability. The experimental observations imply that (1) CO2-rich aqueous fluids have significant impact on the evolution of fracture permeability and may influence (and increase) shale gas production; (2) shale mineralogy, especially calcite mineral, decides the chemical reaction and permeability increasing when CO2-rich aqueous fluids flow through fractures by free-face dissolution effect; (3) clay mineral swelling reduces fracture aperture and additively calcite pressure solution removes the bridging asperities, which are the main reasons for fracture permeability decrease; (4) competition roles among clay mineral swelling, mineral pressure solution, and free-face dissolution determine how fracture permeability changes. Furthermore, a multiple parameter model is built to analyze effective hydraulic aperture evolution in considering above three mechanisms, which provide a reference to forecast fracture permeability evolution in shale formations.

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Nonlinear Flow Characteristics of a System of Two Intersecting Fractures with Different Apertures

Processes ◽

10.3390/pr6070094 ◽

2018 ◽

Vol 6 (7) ◽

pp. 94 ◽

Cited By ~ 4

Author(s):

Richeng Liu ◽

Yujing Jiang ◽

Hongwen Jing ◽

Liyuan Yu

Keyword(s):

Numerical Simulation ◽

Pressure Difference ◽

Critical Pressure ◽

Stokes Equations ◽

Nonlinear Flow ◽

Fracture Aperture ◽

Simulation Code ◽

Hydraulic Aperture ◽

Mechanical Aperture ◽

Forchheimer’S Law

The nonlinear flow regimes of a crossed fracture model consisting of two fractures have been investigated, in which the influences of hydraulic gradient, surface roughness, intersecting angle, and scale effect have been taken into account. However, in these attempts, the aperture of the two crossed fractures is the same and effects of aperture ratio have not been considered. This study aims to extend their works, characterizing nonlinear flow through a system of two intersecting fractures with different apertures. First, three experiment models with two fractures having different apertures were established and flow tests were carried out. Then, numerical simulations by solving the Navier-Stokes equations were performed and the results compared with the experiment results. Finally, the effects of fracture aperture on the critical pressure difference and the ratio of hydraulic aperture to mechanical aperture were systematically analyzed. The results show that the numerical simulation results agree well with those of the fluid flow tests, which indicates that the visualization techniques and the numerical simulation code are reliable. With the increment of flow rate, the pressure difference increases first linearly and then nonlinearly, which can be best fitted using Forchheimer’s law. The two coefficients in Forchheimer’s law decrease with the increasing number of outlets. When increasing fracture aperture from 3 mm to 5 mm, the critical pressure difference increases significantly. However, when continuously increasing fracture aperture from 5 mm to 7 mm, the critical pressure difference changes are negligibly small. The ratio of hydraulic aperture to mechanical aperture decreases more significantly for a fracture that has a larger aperture. Increasing fracture aperture from 5 mm to 7 mm, that has a negligibly small effect on the critical pressure difference will however significantly influence the ratio of hydraulic aperture to mechanical aperture.

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LAB-SCALE MODELING OF PORE FLUID FLOW IN SAMPLES OF MANMADE SUBSTANCE FROM TAILINGS PONDS

Физико-технические проблемы разработки полезных ископаемых ◽

10.15372/ftprpi20190504 ◽

2019 ◽

Keyword(s):

Fluid Flow ◽

Pore Fluid ◽

Scale Modeling ◽

Tailings Ponds

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Analysis of Fracture Roughness Control on Permeability Using SfM and Fluid Flow Simulations: Implications for Carbonate Reservoir Characterization

Geofluids ◽

10.1155/2019/4132386 ◽

2019 ◽

Vol 2019 ◽

pp. 1-19 ◽

Cited By ~ 9

Author(s):

Miller Zambrano ◽

Alan D. Pitts ◽

Ali Salama ◽

Tiziano Volatili ◽

Maurizio Giorgioni ◽

...

Keyword(s):

Fluid Flow ◽

Reservoir Characterization ◽

Flow Simulation ◽

Carbonate Reservoir ◽

Single Fracture ◽

Parallel Plates ◽

Surface Mapping ◽

Navier Stokes Equation ◽

Hydraulic Aperture ◽

Fracture Modeling

Fluid flow through a single fracture is traditionally described by the cubic law, which is derived from the Navier-Stokes equation for the flow of an incompressible fluid between two smooth-parallel plates. Thus, the permeability of a single fracture depends only on the so-called hydraulic aperture which differs from the mechanical aperture (separation between the two fracture wall surfaces). This difference is mainly related to the roughness of the fracture walls, which has been evaluated in previous works by including a friction factor in the permeability equation or directly deriving the hydraulic aperture. However, these methodologies may lack adequate precision to provide valid results. This work presents a complete protocol for fracture surface mapping, roughness evaluation, fracture modeling, fluid flow simulation, and permeability estimation of individual fracture (open or sheared joint/pressure solution seam). The methodology includes laboratory-based high-resolution structure from motion (SfM) photogrammetry of fracture surfaces, power spectral density (PSD) surface evaluation, synthetic fracture modeling, and fluid flow simulation using the Lattice-Boltzmann method. This work evaluates the respective controls on permeability exerted by the fracture displacement (perpendicular and parallel to the fracture walls), surface roughness, and surface pair mismatch. The results may contribute to defining a more accurate equation of hydraulic aperture and permeability of single fractures, which represents a pillar for the modeling and upscaling of the hydraulic properties of a geofluid reservoir.

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