Analytical model for uncertainty characterization of fracture intensity measurement in rock masses

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
Yu-Chen Lu ◽  
Yong-Ming Tien ◽  
Charng Hsein Juang ◽  
Himatul Farichah ◽  
Che-Jui Hsu ◽  
...  
Keyword(s):  
Analytical Model ◽  
Intensity Measurement ◽  
Rock Masses ◽  
Uncertainty Characterization ◽  
Fracture Intensity

2D quantitative analysis of fractures from high-resolution photos for the geomechanical characterization of rock masses

2021 ◽  
Author(s):  
Emmanuel Wyser ◽  
Lidia Loiotine ◽  
Charlotte Wolff ◽  
Gioacchino Francesco Andriani ◽  
Michel Jaboyedoff ◽  
...  
Keyword(s):  
High Resolution ◽  
Point Clouds ◽  
Mitigation Measures ◽  
Future Perspective ◽  
Rock Masses ◽  
Sampling Errors ◽  
Discontinuity Sets ◽  
Adverse Weather ◽  
Geomechanical Characterization

<p>The identification of discontinuity sets and their properties is among the key factors for the geomechanical characterization of rock masses, which is fundamental for performing stability analyses, and for planning prevention and mitigation measures as well.<br>In practice, discontinuity data are collected throughout difficult and time-consuming field surveys, especially when dealing with areas of wide extension, difficult accessibility, covered by dense vegetation, or with adverse weather conditions. Consequently, even experienced operators may introduce sampling errors or misinterpretations, leading to biased geomechanical models for the investigated rock mass.<br>In the last decades, new remote techniques such as photogrammetry,<em> Light Detection and Ranging</em> (LiDAR), <em>Unmanned Aerial Vehicle</em> (UAV) and <em>InfraRed Thermography </em>(IRT) have been introduced to overcome the limits of conventional surveys. We propose here a new tool for extracting information on the fracture pattern in rock masses, based on <em>remote sensing </em>methods, with particular reference to the analysis of high-resolution georeferenced photos. The first step consists in applying the <em>Structure from Motion</em> (SfM) technique on photos acquired by means of digital cameras and UAV techniques. Once aligned and georeferenced, the orthophotos are exported in a GIS software, to draw the fracture traces at an appropriate scale. We developed a MATLAB routine to extract information on the geostructural setting of rock masses by performing a quantitative 2D analysis of the fracture traces, based on formulas reported in the literature. The code was written by testing few experimental and simple traces and was successively validated on an orthophoto from a real case study.<br>Currently, the script plots the fracture traces as polylines and calculates their orientation (strike) and length. Subsequently, it detects the main discontinuity sets by fitting an experimental composite Gaussian curve on histograms showing the number of discontinuities according to their orientation, and splitting the curve in simpler Gaussian curves, with peaks corresponding to the main discontinuity sets.<br>Then, for each set, a linear scanline intersecting the highest number of traces is plotted, and the apparent and real spacing are calculated. In a second step, a grid of circular scanlines covering the whole area where the traces are located is plotted, and the mean trace intensity, trace density and trace length estimators are calculated.<br>It is expected to test the presented tools on other case studies, in order to optimize them and calculate additional metrics, such as persistence and block sizes, useful to the geomechanical characterization of rock masses.<br>As a future perspective, a similar approach could be investigated for 3D analyses from point clouds.</p>

Analysis of Pressure Interference Tests in Unconventional Gas Reservoirs: A Gas Condensate Example from Montney Formation

2021 ◽  
Author(s):  
Behjat Haghshenas ◽  
Farhad Qanbari
Keyword(s):  
Analytical Model ◽  
Hydraulic Fracture ◽  
Transient Analysis ◽  
Gas Condensate ◽  
Production Well ◽  
Monitoring Well ◽  
Interference Test ◽  
Shale Reservoirs ◽  
Montney Formation

Abstract Characterization of hydraulic fracture system in multi-fractured horizontal wells (MFHW) is one of the key steps in well spacing optimization of tight and shale reservoirs. Different methods have been proposed in the industry including core-through, micro-seismic, off-set pressure data monitoring during hydraulic fracturing, pressure depletion mapping, rate-transient analysis, pressure-transient analysis, and pressure interference test. Pressure interference test for a production and monitoring well pair includes flowing the production well at a stable rate while keeping the monitoring well shut-in and recording its pressure. In this study, the coupled flow of gas in hydraulic fractures and matrix systems during pressure interference test is modeled using an analytical method. The model is based on Laplace transform combined with pseudo-pressure and pseudo-time. The model is validated against numerical simulation to make sure the inter-well communication test is reasonably represented. Two key parameters were introduced and calculated with time using the analytical model including pressure drawdown ratio and pressure decline ratio. The model is applied to two field cases from Montney formation. In this case, two wells in the gas condensate region of Montney were selected for a pressure interference test. The monitoring well was equipped with downhole gauges. As the producing well was opened for production, the bottom-hole pressure of the monitoring well started declining at much lower rate than the production well. The pressure decline rate in the monitoring well eventually approached that of the producing well after days of production. This whole process was modeled using the analytical model of this study by adjusting the conductivity of the communicating fractures between the well pairs. This study provides a practical analytical tool for quantitative analysis of the interference test in MFHWs. This model can be integrated with other tools for improved characterization of hydraulic fracture systems in tight and shale reservoirs.

Stochastic Characterization of Epoxies to Predict Performance Uncertainty of Photonic Packages

2004 ◽  
Author(s):  
S. Radhakrishnan ◽  
G. Subbarayan ◽  
L. Nguyen ◽  
W. Mazotti
Keyword(s):  
Analytical Model ◽  
Stochastic Analysis ◽  
Coupling Efficiency ◽  
Viscoelastic Behavior ◽  
Material Behavior ◽  
Considerable Uncertainty ◽  
Stochastic Characterization ◽  
Degree Of Confidence ◽  
Extensive Experimental Data

There is considerable uncertainty in the prediction of performance of a system mainly due to idealizations in geometry, material behavior, and loading history. Uncertainties in geometry can be predicted and controlled using tighter tolerances. However, the models currently used to describe material behavior are mostly deterministic. To predict the coupling efficiency of a photonic system to greater degree of confidence, stochastic analysis procedures are necessary. As part of this analysis, the behavior of materials must be stochastically characterized. In this paper, we present extensive experimental data on thermally and UV-cured epoxies typically used in photonic packages to enable stochastic analysis. The test data includes the viscoelastic behavior. We present analytical model to obtain the variation in the displacement of the epoxies resulting from its stochastic viscoelastic behavior. We utilize the analytical model to predict the uncertainty in the coupling efficiency of a generic photonic package.

Using cave data for improving the reliability of karst groundwater flow models

2020 ◽  
Author(s):  
Mario Parise ◽  
Isabella Serena Liso
Keyword(s):  
Carbonate Rock ◽  
Soil Mechanics ◽  
Main Direction ◽  
Image Process ◽  
Rock Masses ◽  
Variable Size ◽  
Flow Models ◽  
Bedding Planes ◽  
Karst Processes

<p>Rock masses are typically anisotropic and heterogeneous, due to presence of sin-sedimentary discontinuities as bedding planes and of post-depositional features such as joints and faults. When compared to soil mechanics, therefore, a greater complexity of the simulation models for rock masses derives, which is further increased when dealing with carbonate rock masses. Beside the aforementioned types of discontinuities, other features are produced by karst processes; these latter are able to create highly complex networks of voids and conduits, with passages of variable size, which may reach dimensions enterable by man. These features definitely represent the larger discontinuity families within carbonate rock masses, in terms of size, frequency, and pervasiveness, and significantly control the flow of water.</p><p>The peculiar characteristics of karst require dedicated approaches to take into the due account the presence of its typical landforms (voids, conduit/caves of variable size, swallow holes, etc.), and their variable functionality as well. Ignoring karst features in the analysis and characterization of carbonate rock masses, any approach followed, or model implemented, will inevitably result in too great uncertainties (if not errors), and in incorrect information to the engineers.</p><p>What stated above is true also as regards the study of water flow in fractured carbonate rock masses, that cannot be initiated without considering the stratigraphic and structural discontinuity families. To implement flow models scholars typically start from traditional structural-geological surveys, characterization of rock masses through the classical geomechanical approaches, and elaboration of outcrop pictures elaborated by means of image process softwares. The statistical outcomes are then used as parameters in mathematical models, where also the hydrogeological boundary conditions need to be defined.</p><p>A significant step forward in this approach is the use of data directly collected underground, through surveys within the cave systems. The data so collected can be used with a two-fold goal: first, to add a view from the inside of the karst underground landscapes to what is generally observed only at the surface; second, to validate the models, when these are initially implemented only with surface data.</p><p>Plan maps of explored cave systems may be useful to determine in first approximation the main direction of development of the karst processes. Reliable maps of caves are nowadays available, that can be used to extract the main direction of karstification, as well as the average size of the explored karst conduits and passages. All these informations are precious underground-truth data that are definitely worth to be included in hydrogeological models aimed at improving them and their reliability as well.</p><p> </p>

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