Cementation exponent as a geometric factor for the elastic properties of granular rocks

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. MR341-MR349
Author(s):  
Tongcheng Han ◽  
Zhoutuo Wei ◽  
Li-Yun Fu
Keyword(s):  
Elastic Properties ◽  
Geophysical Methods ◽  
Effective Medium ◽  
Geometric Factor ◽  
Rock Properties ◽  
Modeling Approaches ◽  
The Earth ◽  
Elastic Rock ◽  
Effective Medium Models ◽  
Electromagnetic Surveys

A geometric factor properly describing the microstructure of a rock is compulsory for effective medium models to accurately predict the elastic and electrical rock properties, which, in turn, are of great importance for interpreting data acquired by seismic and electromagnetic surveys, two of the most important geophysical methods for understanding the earth. Despite the applications of cementation exponent for the successful modeling of electrical rock properties, however, there has been no demonstration of cementation exponent as the geometric factor for the elastic rock properties. We have developed a workflow to model the elastic properties of clean and normal granular rocks through the combination of effective medium modeling approaches using cementation exponent as the geometric factor. Based on the dedicated modeling approaches, we find that cementation exponent can be adequately used as a geometric factor for the elastic properties of granular rocks. Further results highlight the effects of cementation exponent on the elastic and joint elastic-electrical properties of granular rocks. The results illustrate the promise of cementation exponent as a geometric link for the joint elastic-electrical modeling to better characterize the earth through integrated seismic and electromagnetic surveys.

ULTRASONIC ANGLE-DEPENDENT REFLECTIVITY IN COMPLEX ROCKS FOR IMPROVED INTERPRETATION OF SONIC AND ULTRASONIC LOGS

2021 ◽  
Author(s):  
Daria Olszowska ◽  
◽  
Gabriel Gallardo-Giozza ◽  
Carlos Torres-Verdín ◽  
◽  
...  
Keyword(s):  
Reflection Coefficient ◽  
Elastic Properties ◽  
Rock Properties ◽  
Laboratory System ◽  
Porous Rocks ◽  
Transmission Method ◽  
Reflected Waves ◽  
Acquisition Mode ◽  
Open Hole ◽  
Elastic Rock

Porous rocks are rarely homogeneous. Significant spatial variations in elastic properties are often observed in rocks due to depositional, diagenetic, and structural processes. In laminated sandstones, complex carbonates, or unconventional formations, elastic properties can vary on scales from millimeters to tens of meters. Detection of inhomogeneities and their size in rocks is crucial for fracture propagation design, height containment assessment, and for improving well/reservoir productivity. Most laboratory techniques used to measure rock elastic properties fail to distinguish mid-scale anisotropy; results are subject to spatial averaging effects. We introduce a new experimental method to measure continuous compressional- and shear-wave logs of core samples based on measurements of angle-dependent ultrasonic reflection coefficients. Simultaneously with reflected waves, we detect and interpret refracted waves as an independent way to estimate acoustic wave velocities to support the analysis. Our laboratory system is equipped with an array of receivers to continuously collect measurements. At each core location, we acquire acoustic waveforms at multiple transmitter-receiver angles using a pitch-catch acquisition mode (similar to standard sonic tools). This acquisition mode uses multiple receivers, allowing us to obtain measurements at different incidence angles without moving the sample and keeping the distance traveled by reflected waves constant, thereby eliminating the need for geometrical spreading corrections in reflection-coefficient calculations. Reflectivity-vs.-angle measurements are then matched with numerical simulations to estimate rock elastic properties. Ultrasonic reflection-coefficient measurements are successfully used to estimate dynamic elastic rock properties of homogeneous and layered rock samples. For homogenous samples, values are within a 5% range when compared to those obtained with the standard acoustic transmission method. Measurements acquired on natural and artificially constructed samples show significant departures from homogeneous behavior caused by layering. Laboratory reflection-coefficient measurements enable detection of inch-scale anisotropy within the rock, leading to improved assessment of formation elastic properties. Furthermore, continuous core measurements provide high-resolution reflection-coefficient information which is complementary to open-hole ultrasonic logs.

AN ADVANCED PETROPHYSICAL ORIENTED NUMERICAL METHOD FOR RELIABLE ASSESSMENT OF MECHANICAL PROPERTIES IN CARBONATE FORMATIONS AT THE PORE-SCALE DOMAIN

2021 ◽  
Author(s):  
Mehdi Teymouri ◽  
◽  
Zoya Heidari ◽  
Keyword(s):  
Mechanical Properties ◽  
Spatial Distribution ◽  
Pore Structure ◽  
Pore Pressure ◽  
Elastic Properties ◽  
Hydraulic Properties ◽  
Effective Medium ◽  
Pore Scale ◽  
Micro Scale ◽  
Effective Medium Models

Assessment of effective mechanical properties such as elastic properties and brittleness can be challenging in the presence of complex rock composition, pore structure, and spatial distribution of minerals, especially in the absence of acoustic measurements. Conventional methods such as effective medium modeling, are not reliable for assessments of mechanical properties in complex formations such as carbonates, because solid skeleton of carbonates does not consist of granular minerals with ideal shapes. The effective medium models also overlook both the spatial distribution of petrophysical properties, and the coupled hydraulic and mechanical (HM) processes, which causes significant uncertainties in geomechanical evaluations. The objective of this paper is to develop a numerical method to enhance assessment of effective mechanical properties of anisotropic and heterogenous carbonate formations by modeling the variation of effective stress and the evolution of corresponding strain. The developed method takes into account the coupled HM processes, the realistic spatial distribution of rock inclusions (i.e., rock fabrics), dynamic fluid flow, pore pressure, and pore structure. To achieve this objective, we develop a pore-scale numerical simulator by satisfying conservation equations and considering the coupling among relevant HM phenomena. We adopt peridynamic theory to discretize the micro-scale medium. The inputs to our numerical modeling include pore-scale images of rock samples as well as mechanical and hydraulic properties of each rock inclusion. We perform image processing on micro-CT scan images of rock samples to obtain a realistic micro-scale structure of both rock matrix (i.e., concentration, spatial distribution, and shape of rock constituents) and pore space. We then assign realistic mechanical and hydraulic properties to each rock constituent within the pore-scale medium. The outcomes of numerical modeling include the variation of effective stress and the evolution of corresponding strain by honoring the variability in mechanical/hydraulic properties of rock inclusions caused by their spatial distribution, pore pressure, pore structure, natural fractures, and dynamic fluid flow at the micro-scale domain. We then compare the outcomes of numerical models with the mechanical properties estimated based on effective medium models. We performed sensitivity analyses to quantify the effects of concentration and spatial distribution of rock constituents, divergence in spatial distribution of petrophysical, mechanical, and hydraulic properties of inclusions, pore structure and natural micro-fractures, and pore pressure on variations in effective elastic properties of rock samples. We estimated the elastic properties from the stress/strain curves obtained from numerical simulations. We observed significant errors (more than 30.6% relative error depending on the content and distribution of rock constituents) in estimated effective elastic properties by the effective medium models. These errors are due to overlooking the coupled HM analysis, the spatial distribution, actual shape and size of inclusions, pore-structure, and natural micro-fractures by such effective medium models. The presented advanced pore-scale numerical analysis will (a) enhance reliable assessments of effective elastic/mechanical properties of carbonates or any other rock type in the presence of pore pressure and dynamic flow, and (b) assist upscaling techniques for reliable geomechanical evaluation and assessment of fracture propagation in these formations at larger scales.

Textures and Microstructures in Peridotites from the Finero Complex (Ivrea Zone, Alps) and their Influence on the Elastic Rock Properties

2010 ◽  
Vol 160 ◽  
pp. 183-188 ◽  
Author(s):  
K. Ullemeyer ◽  
B. Leiss ◽  
M. Stipp
Keyword(s):  
Elastic Properties ◽  
Elastic Anisotropy ◽  
Earth’S Crust ◽  
Rock Properties ◽  
Ivrea Zone ◽  
Seismic Experiment ◽  
Internal Structures ◽  
Earth's Crust ◽  
Elastic Rock

In order to quantify differences in the elastic rock properties as a result of fabric differences, peridotite samples from the Finero complex were investigated with respect to their mineral textures and elastic properties. Our data indicate only weak to intermediate texture strengths and weak elastic anisotropy, which is too small to produce a significant acoustic contrast in a seismic experiment. Consequently, internal structures from peridotite bodies in the Earth's crust with such fabric characteristics cannot be resolved reliably.

Effect of Fluids on the Elastic Properties of 3D-Printed Anisotropic Rock Models

2021 ◽  
Vol 62 (5) ◽  
pp. 537-552
Author(s):  
Suresh Dande ◽  
◽  
Robert R. Stewart ◽  
Nikolay Dyaur ◽  
◽  
...  
Keyword(s):  
Wave Propagation ◽  
Elastic Properties ◽  
P Wave ◽  
Engine Oil ◽  
Rock Properties ◽  
Anisotropic Rock ◽  
Wave Velocities ◽  
Inclusion Model ◽  
3D Printed ◽  
Primary Porosity

Laboratory physical models play an important role in understanding rock properties and wave propagation, both theoretically and at the field scale. In some cases, 3D-printing technology can be adopted to construct complex rock models faster, more inexpensively, and with more specific features than previous model-building techniques. In this study, we use 3D-printed rock models to assist in understanding the effects of various fluids (air, water, engine oil, crude oil, and glycerol) on the models’ elastic properties. We first used a 3D-printed, 1-in. cube-shaped layered model. This model was created with a 6% primary porosity and a bulk density of 0.98 g/cc with VTI anisotropy. We next employed a similar cube but with horizontal inclusions embedded in the layered background, which contributed to its total 24% porosity (including primary porosity). For air to liquid saturation, P-velocities increased for all liquids in both models, with the highest increase being with glycerol (57%) and an approximately 45% increase for other fluids in the inclusion model. For the inclusion model (dry and saturated), we observed a greater difference between two orthogonally polarized S-wave velocities (Vs1 and Vs2) than between two P-wave velocities (VP0 and VP90). We attribute this to the S2-wave (polarized normal to both the layering and the plane of horizontal inclusions), which appears more sensitive to horizontal inclusions than the P-wave. For the inclusion model, Thomsen’s P-wave anisotropic parameter (ɛ) decreased from 26% for the air case to 4% for the water-saturated cube and to 1% for glycerol saturation. The small difference between the bulk modulus of the frame and the pore fluid significantly reduces the velocity anisotropy of the medium, making it almost isotropic. We compared our experimental results with theory and found that predictions using Schoenberg’s linear slip theory combined with Gassmann’s anisotropic equation were closer to actual measurements than Hudson’s isotropic calculations. This work provides insights into the usefulness of 3D-printed models to understand elastic rock properties and wave propagation under various fluid saturations.

Transient electromagnetic fields of a buried horizontal magnetic dipole

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. E481-E491 ◽  
Author(s):  
Andrei Swidinsky ◽  
Misac Nabighian
Keyword(s):  
Electric Field ◽  
Magnetic Dipole ◽  
Time Domain ◽  
Major Axis ◽  
Secondary Response ◽  
Burial Depth ◽  
Transient Electromagnetic ◽  
The Earth ◽  
Smoke Ring ◽  
Electromagnetic Surveys

Electromagnetic surveys using a vertical transmitter loop are common in land, marine, and airborne geophysical exploration. Most of these horizontal magnetic dipole (HMD) systems operate in the frequency domain, measuring the time derivative of the induced magnetic fields, and therefore a majority of studies have focused on this subset of field measurements. We examine the time-domain electromagnetic response of a HMD including the electric fields and corresponding smoke rings produced in a conductive half-space. Cases of a dipole at the surface and buried within the earth are considered. Results indicate that when the current in the transmitter is rapidly switched off, a single smoke ring is produced within the plane of the vertical transmitter loop, which is then distorted by the air-earth interface. In this situation, the circular smoke ring, which would normally diffuse symmetrically away from the source in a whole space, is approximately transformed into an ellipse, with a vertical major axis at an early time and a horizontal major axis at a late time. As measured from the location of the transmitter, the depth of investigation and lateral footprint of such a system increases with burial depth. It is also observed that the electric field measured in the direction of the magnetic dipole only contains a secondary response related to the charge accumulation on any horizontal conductivity boundaries because the primary field is always absent. This field component can be expressed analytically in terms of a static and time-varying field, the latter term adding spatial complexity to the total horizontal electric field at the earth surface at early times. Applications of this theoretical study include the design of time-domain induction-logging tools, crossborehole electromagnetic surveys, underground mine expansion work, mine rescue procedures, and novel marine electromagnetic experiments.

Using rock physics models to validate rock composition from multimineral log analysis

Geophysics ◽  
2021 ◽  
pp. 1-69
Author(s):  
Liwei Cheng ◽  
Manika Prasad ◽  
Reinaldo J. Michelena ◽  
Ali Tura ◽  
Shamima Akther ◽  
...  
Keyword(s):  
Quality Control ◽  
Reservoir Characterization ◽  
Rock Physics ◽  
Inequality Constraint ◽  
Effective Medium ◽  
Carbonate Reservoir ◽  
Log Analysis ◽  
Evaluation Tool ◽  
Rock Composition ◽  
Effective Medium Models

Multimineral log analysis is a quantitative formation evaluation tool for geological and petrophysical reservoir characterization. Rock composition can be estimated by solving equations that relate log measurements to the petrophysical endpoints of minerals and fluids. Due to errors in log data and uncertainties in petrophysical endpoints of constituents, we propose using effective medium models from rock physics as additional independent information to validate or constrain the results. In this paper, we examine the Voigt-Reuss (VR) bound model, self-consistent approximation (SCA), and differential effective medium (DEM). The VR bound model provides the first-order quality control of multimineral results. We first show a conventional carbonate reservoir study with intervals where the predicted effective medium models from multimineral results are inconsistent with the measured elastic properties. We use the VR bound model as an inequality constraint in multimineral analysis for plausible alternative solutions. SCA and DEM models provide good estimates in low porosity intervals and imply geological information for the porous intervals. Then, we show a field case of the Bakken and Three Forks formations. A linear interpolation of the VR bound model helps validate multimineral results and approximate the elastic moduli of clay. There are two major advantages to use our new method (a) rock physics effective medium models provide independent quality control of petrophysical multimineral results, and (b) multimineral information leads to realistic rock physics models.

Pengantar Geofisika

2020 ◽  
Author(s):  
Muhammad Syukri ◽  
Keyword(s):  
Geophysical Methods ◽  
Magnetic Method ◽  
Scientific Concept ◽  
Physical Parameters ◽  
Study Program ◽  
The Earth ◽  
Engineering Study ◽  
Close Relationship ◽  
Study Programs ◽  
The Relationship

This introductory book on Geophysics was created to support teaching materials for basic subjects in the Geophysical Engineering Study Program, Physics Study Program, and related Study Programs in addition to other major books. This book introduces the basics of the earth and the structure of the earth, as well as the layers of the earth globally. Furthermore, it is also shown how the relationship between geophysics and other related branches of science within the sphere of geoscience. So that each scientific concept is clearly distinguished, although sometimes there is a very close relationship. In another section, various geophysical methods are described, starting from the basic theory, working principles, approaches and applications. All physical parameters that are applied from each discussion such as seismic method, geoelectric method and IP, gravity method, georadar method, and magnetic method. The hope is that this book can provide benefits for readers and enthusiasts of geoscience.

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