Secondary Wave Velocity Research Articles

The theory of compression–shear coupled composite wave propagation in rock

AbstractThe wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic. In this paper, a compression–shear coupled nonlinear elastic constitutive relation is established, which is consistent with the mechanical properties of rock and mineral medium under high pressure. On this basis, numerical solutions of the wave equation and plane wave analytical solutions for the primary and secondary wave velocities are obtained. As is indicated by the comparison with the linear elastic constitutive theory, the results reflect the compression–shear coupling characteristics of the rock, including the stress path effect and the compression–shear coupling wave effect. With different parameter values, the velocity of the secondary wave changes from lower than that of the elastic shear wave, to higher than that of the elastic shear wave. The research results are expected to provide meaningful explanations for the physical mechanisms of the supershear wave and sub‐Rayleigh wave, and guidance for the detection of rock and soil composition and the observation of seismic waves.

Reservoir charaterization using J-atribute as a new attribute to reduce ambiguity in predicting reservoirs

The Amplitude Variation Offset (AVO) technique has often been used to predict the deposition of hydrocarbons. Knott and Zoeppritz developed the AVO method by using values of primary wave velocity (vp), secondary wave velocity (vs) and density. Then, Rutherford and William divide AVO into 4 classes based on intercept and gradient charts. This method is successfully used to predict hydrocarbons. However, in some cases there are still ambiguities and misinterpretations such as those occurring in oil and water which assess large porosity and similar characters, so that in this study required a new AVO attribute proposed by the name J-attribute to study hydrocarbons and use ambiguous in the results interpretation. The J-attribute method is a new method in Indonesia, which has not yet been tried in the Indonesian field so this research wants to prove the working principle of the J-attribute method required to provide maximum results in determining the fluid. This method is carried out in the Fauna Field, which is made in the North Sumatra Basin. The data used in this study 3 wells equipped with markers and log data such as Gamma Ray, SP, Caliper, Neutron Porosity, Density, Resistivity, DT, Photoelectric, and check shot.

Acoustics and petrophysical investigations on upper cretaceous carbonate rocks from northern Lebanon

Carbonate rocks represent significant aquifers and reservoir rocks in many parts of the world. In this study, twenty-one carbonate samples collected from the exposed rocks at Batroun and Chekka, northern Lebanon, are studied to investigate their lithological characteristics, nannofossil content, and their acoustic and petrophysical properties. Four microfacies are recognized in the studied rocks including packstone, wackstone, wack-mudstone, and the wack-packstone. Nannofossils are detected in the top part of the studied section indicating marine-type depositional conditions for the upper Cretaceous carbonate rocks. The Petrographic analysis revealed also that the studied rocks have moderate to high porosity which is consistent with the measured porosity on core samples. The low porosity of some samples is induced by cementation, which also reduced their permeability. The bulk density varies widely because of the many diagenetic processes that impacted the studied rocks. Moreover, because the primary and secondary wave velocities (Vp, and Vs) are greatly influenced by porosity and density, the samples exhibit extreme variations in acoustic velocities from low values which characterize soft, highly-porous, rocks to higher velocities which are characteristic of compact, massive, and highly-cemented carbonates. Some relationships between the measured petrophysical and acoustic parameters are studied to investigate their mutual dependence, and discuss the impacts of rock composition and diagenetic alterations on the petrophysical properties of the collected rocks. The obtained results are also important in characterizing their mechanical strength, and in the analysis of seismic reflection profiles acquired for equivalent offshore limestone reservoirs in the Levant and the Eastern Mediterranean regions.

Subsonic to Intersonic Transition in Sliding Friction for Soft Solids.

We perform friction experiments between a compliant gel and a rigid cylinder at sliding velocities comparable to the Rayleigh wave or secondary wave velocity of the gel. We find that, when the sliding velocity exceeds the wave velocities, the contact state transitions from Hertzian like to flat punch like, resulting in the breakdown of the lubricating oil film and the abrupt increase in the friction coefficient. We succeed in deriving theoretical solutions for the contact pressure distributions and the deformation profiles in the presence of friction, which are consistent with our experimental observations.

Petrophysical and acoustic characteristics of Jurassic and Cretaceous rocks from Central Lebanon

We conducted several petrophysical and acoustic measurements on 49 core samples collected from the Jurassic and Cretaceous strata exposed at west central Lebanon to evaluate their petrophysical and elastic properties and study the effects of the depositional conditions, sediment composition, and subsequent diagenetic processes on the measured parameters. First, these rocks were petrographically studied to identify their facies, porosity, and the main diagenetic features. In addition, these rocks were investigated under the scanning electron microscope (SEM) and by the X-ray diffraction (XRD) analysis to identify their mineralogy. The petrophysical measurements were performed on the core samples where porosity, permeability, bulk, and grain densities were first determined, followed by measuring the seismic wave velocities under dry and water-saturation conditions. Both carbonates and siliciclastics are encountered in the studied formations. The SEM and XRD analyses revealed that the main constituting minerals are quartz, calcite and dolomite. The studied rocks have generally low to moderate porosity and very low permeability with averages of 0.05, and 0.31 mD, respectively. The bulk density is moderate to high and varies narrowly between 2.03 and 2.79 with an average of 2.64 g/cm3, whereas the average grain density is 2.77 g/cm3. The average primary and secondary wave velocities (Vp and Vs) are 4263, and 2323 m/s, respectively, with an average Vp/Vs of 1.83. Water-saturation has significantly impacted the elastic properties of the studied rocks. From the obtained measurements, we further calculated the elastic coefficients of the studied rocks and constructed several relationships between the measured properties to investigate their mutual interdependence and evaluate the effects of porosity, rock composition, depositional and diagenetic processes on the rock characteristics. We found that some samples, mainly carbonates, deviate significantly from the expected porosity-velocity and density-velocity trends. Originally present micro- and intercrystalline pores and characteristic diagenetic processes in these carbonate rocks, and possibly coring-induced microcracking in few samples, may account for the observed outliers.

Determination of the Geotechnical Characteristics of Hornfelsic Rocks with a Particular Emphasis on the Correlation Between Physical and Mechanical Properties

Geotechnical characteristics and relationships between various physical and mechanical properties were assessed for eight types of hornfelsic rock collected from southern and southwestern parts of the city of Hamedan in western Iran. Rock samples were subjected to mineralogical, physical, index, and mechanical laboratory tests and found to contain quartz, feldspar, biotite, muscovite, garnet, sillimanite, kyanite, staurolite, graphite, and other fine-grained cryptocrystalline matrix materials. Samples had a porphyroblastic texture, and the mineral contents and physical properties influenced various rock characteristics. Some rock characteristics were affected by mineral content, while others were affected by porosity. Dry unit weight, primary and secondary wave velocities, and slake-durability index were noteworthy characteristics affected by mineral content, while porosity had the greatest influence on water absorption, Schmidt hardness, point load index, Brazilian tensile strength, and uniaxial compressive strength. Empirical equations describing the relationships between different rock parameters are proposed for determining the essential characteristics of rock, such as secondary wave velocity, slake-durability index, point load index, Brazilian tensile strength, and uniaxial compressive strength. On the basis of these properties, the studied rocks were classified as being strong or very strong.

Feasible method, utilizing density changes, for estimating in situ dynamic strength and deformation properties of sand samples

Laboratory tests and design reliability are directly controlled by sample quality. The frozen sampling (FS) method is useful for dynamic strength and deformation tests of undisturbed clean sand. However, it is very expensive and requires considerable equipment. The sample quality of Toyoura sands obtained from 48mm and 75mm samplers are scrutinized based on void ratio, dynamic strength and deformation properties through model and cyclic undrained triaxial tests. A conventional method for estimating in-situ dynamic strength and deformation properties of sand samples utilizing density changes is examined and the applicability of the proposed method is discussed for the samples obtained from Niigata sand deposits.The main conclusions obtained from this study are summarized as follows:(1) A conventional method for estimating in-situ void ratio (e0), Dr, stress ratio (RL20) in a 20 cyclic time frame and the initial modulus of rigidity (G0) of sand samples utilizing density changes is proposed.(2) The in-situRL20 and G0 estimated from the proposed method for sand samples from tube samplers were similar to those of frozen sampling and the in-situ modulus of initial rigidity was calculated from the secondary wave velocity for Niigata sand deposits.Therefore, dynamic strength and deformation properties changes, caused by sampling, can be modified appropriately to an in-situ condition by this proposed method.

Modelling Propagation of Stress Waves through Soil Medium for Ground Response Analysis

buildings located at rock sites. Modelling wave propagation through soil medium helps to derive the primary and secondary wave velocities. Most of the time soil mediums are heterogeneous, layered and undergoes nonlinear strains even under weak excitation. The equivalent linear approximation with one dimensional wave propagation is widely adopted for modeling earthquake excitation for layered soil. In this paper, importance of local soil effects, the process of wave propagation through three dimensional elastic medium, layered medium situated on rigid rock, attenuation of stress waves due to material damping, equivalent linear approximation, the concept of one dimensional wave propagation, and a case study of one dimensional wave propagation as a part of site-specific ground response analyses for Delhi region are included. The case study brings out the importance of carrying out site-specific ground response analyses of buildings considering the scenario earthquakes and actual soil conditions for Delhi region.