Assessment of two methods for quantitative measurement of rock fracture aperture

2013 ◽  
pp. 273-277 ◽  
Author(s):  
W Xiao ◽  
R Deng ◽  
C Xia
Keyword(s):  
Quantitative Measurement ◽  
Rock Fracture ◽  
Fracture Aperture

SPONTANEOUS IMBIBITION OF A WETTING FLUID INTO A FRACTURE WITH OPPOSING FRACTAL SURFACES: THEORY AND EXPERIMENTAL VALIDATION

Fractals ◽  
2019 ◽  
Vol 27 (01) ◽  
pp. 1940001 ◽  
Author(s):  
J. W. BRABAZON ◽  
E. PERFECT ◽  
C. H. GATES ◽  
L. J. SANTODONATO ◽  
I. DHIMAN ◽  
...  
Keyword(s):  
Neutron Radiography ◽  
Rock Fracture ◽  
Geometric Mean ◽  
Spontaneous Imbibition ◽  
Future Research ◽  
Fracture Aperture ◽  
Flat Plates ◽  
Fracture Surfaces ◽  
Si Model ◽  
Wetting Fluid

Spontaneous imbibition (SI) is a capillary-driven flow process, in which a wetting fluid moves into a porous medium displacing an existing non-wetting fluid. This process likely contributes to the loss of fracking fluids during hydraulic fracturing operations. It has also been proposed as a method for an enhanced recovery of hydrocarbons from fractured unconventional reservoirs. Numerous analytical and numerical approaches have been employed to model SI. Invariably, these idealize a fracture as the gap formed between parallel flat surfaces. In reality, rock fracture surfaces are rough over multiple scales, and this roughness will influence the contact angle and rate of fluid uptake. We derived an analytical model for the early-time SI behavior within a fracture bounded by parallel impermeable surfaces with fractal roughness assuming laminar flow. The model was tested by fitting it to experimental data for the SI of deionized water into air-filled rock fractures. Twenty cores from two rock types were investigated: a tight sandstone (Crossville) and a gas shale (Mancos). A simple Mode I longitudinal fracture was produced in each core by compressive loading between parallel flat plates using the Brazilian method. Half of the Mancos cores were fractured perpendicular to bedding, while the other half were fractured parallel to bedding. The two main parameters in the SI model are the mean separation distance between the fracture surfaces, [Formula: see text], and the fracture surface fractal dimension [Formula: see text]. The [Formula: see text] was estimated for each core by measuring the geometric mean fracture aperture width through image analysis of the top and bottom faces, while [Formula: see text] was estimated inversely by fitting the SI model to measurements of water uptake obtained using dynamic neutron radiography. The [Formula: see text] values ranged from 45[Formula: see text][Formula: see text]m to 190[Formula: see text][Formula: see text]m, with a median of 93[Formula: see text][Formula: see text]m. The SI model fitted the height of uptake versus time data very well for all of the rock cores investigated; medians of the resulting root mean squared errors and coefficients of determination were 0.99[Formula: see text]mm and 0.963, respectively. Estimates of [Formula: see text] ranged from 2.04 to 2.45, with a median of 2.24. Statistically, all of the [Formula: see text] values were significantly greater than two, confirming the fractal nature of the fracture surfaces. Future research should focus on forward prediction through independent measurements of [Formula: see text] and extension of the existing SI model to late times (through the inclusion of gravity) and fractures with permeable surfaces.

scholarly journals A Quasi-3D Numerical Model for Grout Injection in a Parallel Fracture Based on Finite Volume Method

Complexity ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-18
Author(s):  
Xiaolong Li ◽  
Meimei Hao ◽  
Yanhui Zhong ◽  
Bei Zhang ◽  
Fuming Wang ◽  
...  
Keyword(s):  
Analytical Solution ◽  
Finite Volume Method ◽  
Finite Volume ◽  
Rock Fracture ◽  
Diffusion Mechanism ◽  
Three Dimensional ◽  
Fracture Aperture ◽  
Grout Injection ◽  
New Model ◽  
Volume Method

The purpose of the present work is to develop a quasi-3D numerical method that can be used to study the diffusion mechanism of grout injection in a rock fracture based on the collocated structured grid of the finite volume method (FVM). Considering the characteristics of fracture in geometry that the aperture is much less than its length and width, the Hele-Shaw model is introduced to deduce the z-derivatives of velocities u and v at walls, which is a function of the relevant average velocity and the fracture aperture. The traditional difference scheme for the diffusive term is partly substituted with the derived analytical expressions; hence a three-dimensional problem of grout flow in the parallel fracture can be transformed into a two-dimensional one that concerns fracture aperture. The new model is validated by the analytical solution and experimental data on three cases of grouting in the parallel-plate fracture. Compared with the results from ANSYS-Fluent software, the present model shows better agreement with the analytical solution for the distribution of pressure and velocity. Furthermore, the new model needs less grid unit, spends less time, but achieves greater accuracy. The complexity of the grout flow field in the rock fracture is reduced; thus the computational efficiency can be improved significantly.

Coupled hydromechanical modeling of rock fractures under normal stress

2004 ◽  
Vol 41 (4) ◽  
pp. 686-697 ◽  
Author(s):  
M Bart ◽  
J F Shao ◽  
D Lydzba ◽  
M Haji-Sotoudeh
Keyword(s):  
Experimental Data ◽  
Normal Stress ◽  
Rock Fracture ◽  
Fluid Pressure ◽  
Fracture Aperture ◽  
Rock Fractures ◽  
Compression Tests ◽  
Void Space ◽  
Progressive Fracture ◽  
Single Rock Fracture

In this paper, a nonlinear poromechanical model is developed for a single rock fracture under normal stress. The fracture is represented by a set of voids, and the progressive fracture displacement is considered as a modification process of void space. Based on experimental data obtained from three representative rock fractures, the constitutive model is formulated through an extension of Biot poroelasticity theory to a saturated fracture. A generalized poroelastic coupling coefficient is introduced to describe the interaction between pore fluid pressure and fracture deformation. This coefficient is expressed as a function of fracture aperture. Five parameters involved in the model have been determined from mechanical and poromechanical compression tests. The validity of the model is checked on fluid flow tests under different normal stresses. Comparisons between numerical simulations and experimental data are provided.Key words: hydromechanical coupling, interfaces, joints, poroelasticity, rock mechanics, fractures.

scholarly journals Assessing Risk from DNAPLs in Fractured Aquifers

2002 ◽  
Vol 7 (2) ◽  
pp. 47
Author(s):  
D.N. Lerner ◽  
G.P. Wealthall ◽  
A. Steele
Keyword(s):  
Risk Assessment ◽  
Rock Fracture ◽  
Chlorinated Solvents ◽  
Fundamental Property ◽  
Nonaqueous Phase Liquids ◽  
Fracture Aperture ◽  
Fractured Aquifers ◽  
Phase Saturation ◽  
Hydraulic Aperture

Chlorinated solvents are among the most widespread pollutants of groundwater. As DNAPLs (dense nonaqueous phase liquids), they can move rapidly and in complex patterns through fractures to reach and contaminate large volumes of aquifer, and then dissolve to cause significant pollution of groundwater. However, clean-up of DNAPLs in fractured rocks is virtually impossible and certainly expensive. Risk assessment should be used to decide whether the pollution is serious enough to justify major expenditure on clean-up or containment. A key aspect of risk assessment for DNAPLs in fractured aquifers is to understand how deep they are likely to have penetrated through the fracture network. This paper addresses two aspects of such predictions: measuring fracture apertures in situ and the connectivity of fracture networks with respect to DNAPLs. Fracture aperture is an in-situ field technique that has been developed and implemented to measure aperture variability and NAPL entry pressure in an undisturbed, water-saturated rock fracture. The field experiment also provided the opportunity to measure the wetting phase relative permeability at residual non-wetting phase saturation. The RADIO (Radial Aperture Determination by the Injection of Oil) method employs a constant rate injection of a non-toxic NAPL into a fracture isolated by a double packer array. The method was applied at the field site in Scotland, and measured apertures out to ~5m from the borehole. It showed that hydraulic aperture (from packer tests) was a poor estimator of the controlling aperture for DNAPL movement. This is the first time such large-scale aperture measurements have been made, and the technique is the first which can provide useful aperture estimates for risk analysis of DNAPL movement.Network connectivity is a fundamental property of the fracture system. DNAPL connectivity extends the concept to take account of the fluid properties. 

Conversion of a Micro-CT Scanned Rock Fracture Into a Useful Model

2009 ◽  
Author(s):  
Dustin Crandall ◽  
Grant Bromhal ◽  
Duane H. Smith
Keyword(s):  
Rock Fracture ◽  
Fluid Motion ◽  
Natural Fracture ◽  
Fracture Aperture ◽  
Micro Ct ◽  
Parallel Plates ◽  
Micro Computed Tomography ◽  
Data Set ◽  
Physical Geometry ◽  
Flow Through

Within geologic reservoirs the flow of fluids through fractures is often orders of magnitude greater than through the surrounding, low-permeability rock. Because of the number and size of fractures in geological fields, reservoir-scale discrete-fracture simulators often model fluid motion through fractures as flow through narrow, parallel plates. In reality fractures within rock are narrow openings between two rough rock surfaces. In order to model the geometry of an actual fracture in rock, a ∼9 cm by 2.5 cm fracture within Berea sandstone was created and the aperture distribution was obtained with micro-Computed Tomography (CT) scans by Karpyn et al. [1]. The original scans had a volume-pixel (voxel) resolution of 27 by 27 by 32 microns. This data was up-scaled to voxels with 120 microns to a side to facilitate data transfer and for practicality of use. Using three separate reconstruction techniques, six different fracture meshes were created from this up-scaled data set, each with slightly different final geometries. Flow through each of these fracture meshes was evaluated using the finite-volume simulator FLUENT. While certain features of the fracture meshes, such as the shape of the fracture aperture distributions and overall volume of the void, remained similar between the different geometric reconstructions, the flow in different models was observed to vary dramatically. Rough fracture walls induced more tortuous flow paths and a higher resistance to flow. Natural fractures do vary in-situ, due to sidewall dissolution and mineral precipitation, smoothing and coarsening fracture walls respectively. Thus for our study the range of fracture properties was actually beneficial, allowing us to describe the flow through a range of fracture types. A compromise between capturing the geometric details within a domain of interest and a tractable computational mesh must always be addressed when flow through a physical geometry is modeled. The fine level of detail that is currently available from micro-CT scanning equipment can compound this problem. This study evaluates several methods of obtaining rational CFD meshes from a complex physical geometry, and discusses the benefits and disadvantages of the different procedures as they pertain to flow through a natural fracture in rock.

scholarly journals Numerical Simulation on Non-Darcy Flow in a Single Rock Fracture Domain Inverted by Digital Images

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Jianli Shao ◽  
Qi Zhang ◽  
Wenbin Sun ◽  
Zaiyong Wang ◽  
Xianxiang Zhu
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Digital Images ◽  
Rock Fracture ◽  
Inertial Force ◽  
Darcy Flow ◽  
Fracture Aperture ◽  
Rock Fractures ◽  
Single Rock Fracture ◽  
Fracture Domain

The influence of rock seepage must be considered in geotechnical engineering, and understanding the fluid flow in rock fractures is of great concern in the seepage effect investigation. This study is aimed at developing a model for inversion of rock fracture domains based on digital images and further study of non-Darcy flow. The visualization model of single rock fracture domain is realized by digital images, which is further used in flow numerical simulation. We further discuss the influence of fracture domain geometry on non-Darcy flow. The results show that it is feasible to study non-Darcy flow in rock fracture domains by inversion based on digital images. In addition, as the joint roughness coefficient (JRC) increases or the fracture aperture decreases, distortion of the fluid flow path increases, and the pressure gradient loss caused by the inertial force increases. Both coefficients of the Forchheimer equation decrease with increasing fracture aperture and increase with increasing JRC. Meanwhile, the critical Reynolds number tends to decrease when JRC increases or the fracture aperture decreases, indicating that the fluid tends to non-Darcy flow. This work provides a reference for the study of non-Darcy flow through rock fractures.

Semi‐automatic analysis of rock fracture orientations from borehole wall images

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 129-137 ◽  
Author(s):  
Bhaskar B. Thapa ◽  
Paul Hughett ◽  
Kenzi Karasaki
Keyword(s):  
Hough Transform ◽  
High Intensity ◽  
Input Data ◽  
Rock Fracture ◽  
Fracture Aperture ◽  
Test Cases ◽  
Rock Fractures ◽  
Tunnel Stability ◽  
Noisy Background ◽  
Intensity Contrast

We develop a semiautomatic method of identifying rock fractures and analyzing their orientations from digital images of borehole walls. This method is based on an algorithm related to the Hough transform which is modified to find sinusoidal rather than linear patterns. The algorithm uses the high‐intensity contrast between the fracture aperture and the rock wall, as well as the sinusoidal trajectory defined by the intersection of the borehole and the fracture. The analysis rate of the algorithm itself is independent of fracture contrast and network complexity. The method has successfully identified fractures both in test cases containing several fractures in a noisy background and in real borehole images. The analysis rate was 0.3–1.2 minutes/m of input data, compared to an average of 12 minutes/m using an existing interactive method. An automatic version under development should open new possibilities for site characterization, such as real‐time exploration and analysis of tunnel stability and support requirements as construction proceeds.

A quantitative image analysis method for the determination of cocontinuity in polymer blends

1993 ◽  
Vol 51 ◽  
pp. 894-895
Author(s):  
William A. Heeschen
Keyword(s):  
Image Analysis ◽  
Polymer Blends ◽  
Quantitative Measurement ◽  
Morphological Evolution ◽  
Phase Ratio ◽  
Irregular Shapes ◽  
Quantitative Image ◽  
Discrete Domains ◽  
A Domains

Two new morphological measurements based on digital image analysis, CoContinuity and CoContinuity Balance, have been developed and implemented for quantitative measurement of morphology in polymer blends. The morphology of polymer blends varies with phase ratio, composition and processing. A typical morphological evolution for increasing phase ratio of polymer A to polymer B starts with discrete domains of A in a matrix of B (A/B < 1), moves through a cocontinuous distribution of A and B (A/B ≈ 1) and finishes with discrete domains of B in a matrix of A (A/B > 1). For low phase ratios, A is often seen as solid convex particles embedded in the continuous B phase. As the ratio increases, A domains begin to evolve into irregular shapes, though still recognizable as separate domains. Further increase in the phase ratio leads to A domains which extend into and surround the B phase while the B phase simultaneously extends into and surrounds the A phase.

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