Compressional Velocity Research Articles

Performance evaluation and development of tensile softening law for concrete reinforced with different sizes and combinations of basalt fibers

This research examines the performance of concrete reinforced with different sizes and combinations of basalt fibers (BF). Test parameters comprised the base concrete grade [normal-strength concrete (NSC) and high-strength concrete (HSC)] and BF configuration (short with length of 20 mm, long with length of 50 mm, and hybrid combination at ratio of 1:1). The BF volume fraction (νf) was 1.0%. The tests included slump, compression, splitting, flexure, bulk resistivity, and ultrasonic pulse velocity (UPV). The base concrete grade had no effect on the slump reduction, splitting and flexural strength gains caused by BF when short BF were used. The slump reduction caused by BF was aggravated when long or hybrid BF were used. The use of BF slightly reduced the compressive strength by up to 13%. Short BF resulted in a minor increase of up to 8% in the splitting and flexural strengths, irrespective of the base concrete grade. Hybrid BF resulted in similar or higher splitting and flexural strength gains, except in one case where long BF were more effective. The splitting tensile strength gain caused by long BF was more pronounced for NSC (25%) than HSC (14%). NSC mixtures exhibited higher flexural strength gains (18–20%) than those of their HSC counterparts (10–16%), when long or hybrid BF were used. The use of BF improved the bulk resistivity but had no effect on UPV. Simulation models were developed for the tested concrete prisms. A new tensile softening law was established for BF-reinforced concrete based on inverse analysis of test data.

Estimation of Shear Wave Velocity for Shallow Depth Using Artificial Neural Network Technique: A Case Study in Rumaila oil field

In Rumaila oilfield, the lost circulation problem is a challenging issue. The geological and geomechanical properties of subsurface formations have a role in causing a circulation loss. One of the natural features related to mud loss against these formations is an unconformity surface. Inferring surface unconformity needs to be understood how the mechanical properties of rocks are distributed across the entire reservoir. The result is identifying areas of loss for solving most loss problems. Using well logs, a geomechanical model can be constructed to identify the surface unconformity. Shear wave velocity is the most crucial factor in determining mechanical properties. They are not frequently recorded during well logging for time and cost-saving purposes. save time and cost. To overcome this challenge, an ANNs model was developed to estimate the missing Vs data for the Hasa and Aruma groups in the Rumaila oil field for interested wells from the south and north domes (extending from the top of Dammam to the bottom of Hartha). The performance of the new model was tested through calibration. The outcomes showed that measured depth (MD), bulk density (RHOB), and compressional velocity (Vp) are key parameters for creating the ANN model utilizing. This study has proven that the basic systematic equations are accurately anticipate shear velocity (Vs) from conventional well logs. The correlation coefficient (R2) and the root mean square error were 0.956) and0.118, respectively.The optimum number of hidden neurons was 3 neurons). The presented model is closely resemble the measured Vs data when dataset from other well was used to check the accuracy of that predictive model. This study presents an effective, simple, and cost-effective technique, which can be used in the absence of rock tests and DTs.

Shallow Low‐Velocity Layer in the Hyuga‐Nada Accretionary Prism and Its Hydrological Implications: Insights From a Passive Seismic Array

AbstractShear wave velocity (Vs) estimations of accretionary prisms can pose unique constraints to the physical properties of rocks, which are hard to obtain from compressional velocities (Vp) alone. Thus, it would help better understand the fluid processes of the accretion system. This study investigates the Vs structure of the Hyuga‐nada accretionary prism using an array of ocean‐bottom seismometers (OBSs) with a 2 km radius. Teleseismic Green's functions and a surface wave dispersion curve are inverted to one‐dimensional Vs structures using transdimensional inversion. The results indicate the presence of a low‐velocity zone 3–4 km below the seafloor. The reduced Vs corresponds to a reduced Vp feature obtained in a previous seismic refraction survey, and the high Vp/Vs ratio suggests the presence of high pore fluid pressure. In addition, the resolved lithological boundary exhibits a sharp offset that extends laterally across the OBS array. We attribute this offset to a blind fault below while acknowledging other possibilities, such as due to mud diapirism or intense fracturing. The predicted fault is located at the Kyushu–Palau Ridge flank, oriented roughly parallel to the ridge axis, and thus likely caused by ridge subduction. This fault may act as a fluid conduit, contributing to the formation of a fluid reservoir beneath the compacted sediment layers.

Fast magneto-acoustic wave turbulence and the Iroshnikov–Kraichnan spectrum

An analytical theory of wave turbulence is developed for pure compressible magnetohydrodynamics in the small $\beta$ limit. In contrast to previous works where the multiple scale method was not mentioned and slow magneto-acoustic waves were included, we present here a theory for fast magneto-acoustic waves for which only an asymptotic closure is possible in three dimensions. We introduce the compressible Elsässer fields (canonical variables) and show their linear relationship with the mass density and the compressible velocity. The kinetic equations of wave turbulence for three-wave interactions are obtained and the detailed conservation is shown for the two invariants, energy and momentum (cross-helicity). An exact stationary solution (Kolmogorov-Zakharov spectrum) exists only for the energy. We find a $k^{-3/2}$ energy spectrum compatible with the Iroshnikov–Kraichnan (IK) phenomenological prediction; this leads to a mass density spectrum with the same scaling. Despite the presence of a relatively strong uniform magnetic field, this turbulence is characterized by an energy spectrum with a power index that is independent of the angular direction; its amplitude, however, shows an angular dependence. We prove the existence of the IK solution using the locality condition, show that the energy flux is positive and hence the cascade direct and find the Kolmogorov constant. This theory offers a plausible explanation for recent observations in the solar wind at small $\beta$ where isotropic spectra with a $-3/2$ power-law index are found and associated with fast magneto-acoustic waves. This theory may also be used to explain the IK spectrum often observed near the Sun. Besides, it provides a rigorous theoretical basis for the well-known phenomenological IK spectrum, which coincides with the Zakharov–Sagdeev spectrum for acoustic wave turbulence.

Mechanical Properties of Plastic Concrete Made Using Recycled Aggregates for Paving Blocks

In developing countries, the management of waste continues to be a major challenge, especially in urban areas. One of the major concerns for today’s world is the management of plastic and construction and demolition (C&D) wastes which are increasing with urbanization and population growth. This study aims to explore the possibility of the use of plastic waste as a binder and recycled aggregates obtained from C&D waste to produce concrete paving blocks. The mechanical investigation was carried out to find the optimum content of plastic waste to prepare the plastic concrete. Three different concrete mixes were prepared with plastic contents of 30%, 40%, and 50% by the weight of aggregate. To evaluate the mechanical properties of plastic concrete, compression, flexural, and ultrasonic pulse velocity (UPV) tests were performed on the prepared samples. Cubical specimens of 36 x 40 x 40 mm for compression tests and prismatic specimens of 36 x 40 x 120 mm for flexural tests were cut using a saw from the paving blocks of size 36 x 137 x 290 mm. The results indicated that the strength of plastic concrete increased with the increase in plastic content. The maximum compressive and flexural strength was achieved at 50% plastic content, which was 40.52 MPa and 10.13 MPa, respectively. The compressive and flexural strengths of plastic concrete were compared with the minimum strength requirement specified by various standards specification such as American, Canadian, and Chinese. It was found that plastic concrete with 50% content of plastic waste meets the minimum criteria of mechanical strengths specified in these standards. Presently, many countries of the African continent are facing severe problems of plastic waste. As per the findings of this study, the use of waste plastics in molten form as the only binder in the development of concrete paving blocks could offer a solution for such countries to beneficially manage the plastic waste.

The influence of mantle hydration and flexure on slab seismicity in the southern Central Andes

Knowledge of the causative dynamics of earthquakes along subduction-zone interfaces and within oceanic slabs is relevant for improving future seismic hazard assessments. Here, we combine the analysis of seismic tomography, the 3D structure of the slab and seismicity to investigate the controlling factors driving slab seismic activity beneath the southern Central Andes. We evaluate the ratio distribution between compressional and shear-wave seismic velocities (Vp/Vs) as a proxy for the hydration state of the lithospheric mantle, oceanic slab, and plate interface. Regions of high Vp/Vs, i.e. areas of hydrated mantle, are principally caused by compaction effects and dehydration reactions. In contrast, slab seismicity in areas of low Vp/Vs and inferred lower fluid content in the overriding plate is facilitated by enhanced flexural stresses due to changes in the subduction angle of the oceanic plate. Plate-interface background seismicity correlates with areas of higher Vp/Vs (hydrous interface) at depths <50 km, while areas of most pronounced plate-locking coincide with regions of low Vp/Vs (anhydrous interface). The regions of anhydrous plate interface are likely candidates for future great megathrust events due to their higher potential for elastic energy accumulation compared to more hydrated regions.

Thermoelastic Properties of Liquid Fe‐Rich Alloys Under Martian Core Conditions

AbstractSeismic measurements made on Mars indicate that the liquid iron‐nickel core is rich in light elements; however, the effects of these light components on the elasticity of Mars’ core remain poorly constrained. Here, we calculate elastic properties of various liquid Fe‐X (X = Ni, S, C, O and H) mixtures using ab initio molecular dynamics simulations. We find that, at martian core conditions, the addition of S and O most effectively decreases the density of liquid iron, followed by C and H, while Ni has a minimal effect. As for compressional sound velocity (Vp), C increases Vp of liquid Fe throughout Mars’ core, while both S and O reduce Vp, the intensity of which diminishes with increasing pressure. Assuming a martian core made of a binary mixture, the seismically‐inferred density would require the presence of at least 30 wt% S.

Effects of the size polydispersity and friction coefficient on the compressive strength of wet granular materials

We numerically study the effects of the size polydispersity and the friction coefficient on the compressive strength of wet granules under a diametrical compression test by using discrete element simulations. The nu-merical method is coupled with the capillary cohesion law which is enhanced by the cohesive forces between grains in the pendular regime. The wet granules are composed of primary spherical particles whose size poly-dispersity is varied from1 to 10 and the friction coefficient between grains is varied from0.1 to 1.0. By applying a constant compression velocity on the top plate in quasi-static regime, the granule is deformed but does not abruptly rupture due to the cohesive effects between grains and the rearrangement of primary particles. This no abrupt rupture is characterized by the appearance of the peak compressive stress in a long vertical strain before the onset failure of the granule. The compressive strength of the granule increases with increasing the friction coefficient for all cases of the size polydispersity but seemly declines for low values of the size polydispersity and almost level-off for high-size polydispersity with the friction coefficient larger than 0.5.

Effect of thermal fluctuations on homogeneous compressible turbulence

For more than a century, it has been widely believed that there is a clear gap between molecular motions at the microscopic level and turbulent fluctuations at the macroscopic level. However, recent studies have demonstrated that the thermal fluctuations resulted from molecular motions have nonnegligible effects on the dissipation range of turbulence. To further clarify the reviving debate on this topic, we employ the molecular-level direct simulation Monte Carlo (DSMC) method to simulate homogeneous turbulence with different turbulent Mach numbers, extending the previous studies by considering the effect of compressibility. Our results show that, for both one-dimensional (1D) stationary turbulence and two-dimensional (2D) decaying isotropic turbulence, the turbulent energy spectra are significantly changed due to thermal fluctuations below the spatial scale comparable to the turbulent dissipation length scale. The energy spectra caused by thermal fluctuations for different spatial dimensions d present different scaling laws of the wavenumber k as {{k}^{(d-1)}}. For 2D cases, we show that the effect of thermal fluctuations on the spectrum of compressible velocity component is greatly affected by the change of compressibility. The 2D spectra of density, temperature and pressure are also obtained, showing the same scaling law at large wavenumbers as found for the energy spectra. Moreover, it is found that the effects of thermal fluctuations on the thermodynamic spectra are the same as those on the spectra of compressible velocity component.

Comparative study of elastic properties of marl and limestone layers in the Eagle Ford formation

Eagle Ford Formation has significant heterogeneity due to the existence of marl and interbedded limestone layers. The objective of this paper is to study the elastic properties of different layers in the Eagle Ford Formation. To achieve the goal, the relationships between compressional and shear velocities in marl and limestone layers were investigated in two representative Eagle Ford wells. These empirical equations can be used to estimate the shear velocity in Eagle Ford wells without sufficient well log data. Moreover, correlations between elastic properties and GR were obtained. Among all layers in the Eagle Ford Formation, marl layers of the lower Eagle Ford have the lowest averaged values of compressional velocity, shear velocity and dynamic Young’s modulus, while the limestone layers of the upper Eagle Ford have the highest averaged values of these three elastic parameters. In addition, the effect of elastic properties of shale layers on the aspect ratio of unconfined and confined fractures were evaluated. The influence of Young’s modulus contrast of shale layers on the aspect ratio of confined fractures was remarkable.

A high-performance mini-generator with average power of 2 W for human motion energy harvesting and wearable electronics applications

The sustainability of power supply for mobile electronic devices is a problem that needs to be solved urgently. The energy from human motion is an optimal solution for this problem. As for the traditional energy harvesters based on electromagnetic, triboelectric, and piezoelectric induction, energy management is the largest challenge because of the low conversion efficiency and output power. In this paper, a high-efficiency and high-power energy harvester (EPEH) is presented based on the intersecting beam array structure. It can effectively harvest the pressure energy of humans under the soles at the states of walking, running, and weight-bearing walking. The EPEH does not impair the flexibility of humans compared with joint energy harvesters. The intersecting beam array structure is key component, which can magnify the compression distance in the vertical direction of 3.4 times in the horizontal direction, facilitating maximum energy harvesting within a limited height. On the other hand, the design of rolling friction structure can effectively reduce energy loss and improve energy conversion efficiency. The result shows that the maximum average output power can reach 2 W at 7 km/h. Because of the high output power, the energy management circuits and voltage regulator circuits can be derived and stable work, the energy harvested by the EPEH can be stored in the lithium battery (3.7 V, 50 mAh). Furthermore, the generated energy could supply mobile phones, smart watches, light bulbs, flashlights, children's anti-lost devices, and so on. Through the energy management circuit and voltage regulator circuit (1.5 V and 5 V), the energy conversion efficiency of the device can reach 65.2 % at a compression velocity of 2500 mm/min and a frequency of 1.25 Hz. It is of great significance for the practical application of wearable energy harvesting technology and has multiple application prospects.

МОДЕЛЮВАННЯ ЕФЕКТІВ ЗАМІЩЕННЯ ФЛЮЇДУ У ВІЗЕЙСЬКИХ ВІДКЛАДАХ ЯБЛУНІВСЬКОГО РОДОВИЩА НА ОСНОВІ ІНТЕРПРЕТАЦІЇ ДАНИХ ГДС ТА ПЕТРОФІЗИКИ

The paper discusses the details of the application of the method of fluid substitution which is used for predicting elastic properties of reservoir rocks and their dependence on pore fluid and porosity. This method makes it possible to predict changes in elastic response of a rock saturation with different fluids. The main task of this paper was to study the productive zones of the visean deposits of the Yablunivske field using the example of a single well. The integration of petrophysics and rock physics (Gassmann fluid substitution) was applied to sandstones with intergranular porosity. The objective of the study was to use petrophysical dependences, cross-plots and Gassmann fluid substitution modelling to determine the effect of different pore fluids (brine, oil, gas) on acoustic properties (compressional velocity, shear velocity, density). It was established that the sandstone is a predominant type of reservoir of the considered rocks. The effect of fluid substitution on elastic properties was determined as a result of the implementation of Gasman's technique. The compressional velocity and density decreased, shear velocity slightly increased when brine was substituted with gas for the formed models. Limit values of acoustic impedance and Vp/Vs have been established for the water saturated and hydrocarbon saturated strata of the V-20 – V-22 horizons. It can be used for the drilling new wells of the Yablunivske field creating elastic reservoir rock models.

The Combined Impact of Imposed Loads and Elevated Temperature on Steel Fiber Reinforced Concrete Samples

Reinforced concrete buildings and structures are exposed to fire, and the concrete's qualities can vary in the case of an uncontrolled fire. It is essential to know how concrete's properties may change as a result of exposure to high temperatures and loading for normal concrete with or without fiber reinforcement. Understanding the strength characteristics of concrete structures exposed to high temperatures is important in order to be able to predict how these structures will perform after exposure to this condition. This study investigates the combined impact of loading and high temperature on the properties of concrete samples by testing the compressive, flexural strength, and ultrasonic pulse velocity (UPV) of normal-strength concrete (NSC) with or without steel fiber. The type of steel fiber employed in this investigation is hooked-end steel fiber with a 1% volume fraction of concrete. The concrete samples were subjected to four sustained load cases (0, 20, 40, and 60% of ultimate load) and exposed to elevated temperatures (25, 300, and 500°C) for about 2 hours. In addition, using an unrestrictive test before and after loading and heating, the results indicated the maximum deference of compressive strength decreasing is 4% for the steel fiber (SF1) mixture compared with NSC mixture at 300°C for all load cases. While at 60% sustained load and 500°C, the maximum deference of compressive strength decreasing is 12% for the NSC mixture as compared with the SF1 mixture. The maximum difference in flexural strength is 20% for mixtures with steel fiber (SF1) compared to NSC mixtures at 500°C for all load cases. In addition, the UPV test was used to investigate the microstructure and quality of concrete. This test indicated no difference or approximately equal values for SF1 and NSC mixtures at 25 and 300°C for all load cases, while at 500°C, the UPV test for NSC had a higher value than the UPV value of the SF1 mixture.

Influence of Aspect Ratio on Wave Propagation in Granular Crystals Consisting of Ellipse-Shaped Particles

The behavior of waves in granular materials is very complex and closely related to the macro-micro properties such as particle shape, packing, and particle size distribution. In this study, the influence of the aspect ratio (AR) and confining stress on wave propagation in 2D granular crystals consisting of ellipse-shaped particles is investigated based on discrete element method. The energy attenuation, wave velocity, wavefront shape, and frequency dispersion are mainly focused. The results show that the energy attenuation exhibits an increasing trend with bigger confining stress and smaller AR in the direction of wave propagation. The wave velocities increase with increasing AR, and the relation between compressive wave velocities and the confining stress and AR is obtained. Wavefront has the elliptical shape which has the same AR as elliptical particles of specimen, and its analytical expression is also obtained. The dispersion is affected by AR, which is mainly reflected in the modified particle spacing in sine fitted frequency dispersion curve. Larger confining stress allows a larger maximum frequency, and produces stronger dispersion. The above conclusion can provide a reference for wave-guided granular crystals design.

An improved multiphase lattice Boltzmann flux solver with phase interface compression for incompressible multiphase flows

Numerical dissipation is ubiquitous in multiphase flow simulation. This paper introduces a phase interface compression term into the recently developed multiphase lattice Boltzmann flux solver and achieves an excellent interface maintenance. Here, the phase interface compression term only works in the interface region and is solved as the flux in finite volume discretization. At each cell interface, the interfacial compression velocity ur is determined by local reconstruction velocities of the multiphase lattice Boltzmann flux solver, which maintains the consistency of the flux evaluation. Meanwhile, the interfacial order parameter C in the phase interface compression term is obtained by the second order upwind scheme according to the interface normal direction. Numerical validation of the present model has been made by simulating the Zalesak problem, the single vortex problem, Rayleigh–Taylor instability, and bubble rising and coalescence. The obtained results indicate the validity and reliability of the present model.

DELINEATION OF UNCERTAINTIES IN ANISOTROPIC SHALLOW SUBSURFACE BY INTEGRATED GEOPHYSICAL AND GEOMECHANICAL EXAMINATION

This study focused on geophysical and geomechanical analyses to arbitrate weak zones in Limestone of Gaj formation. Two boreholes were drilled and used to facilitate downhole seismic experiment down to 30 meters of depth. The downhole seismic method was supplied compressional waves velocities for inspection of shallow subsurface properties to evaluate local site condition. The primary data of P-waves velocities are varying from 566 m/s to 1225 m/s (BH-1) 570 m/s to 1320 m/s (BH-2). The information of elastic moduli were derived from primary waves data through empirical relationships. The core samples were collected and examined for geotechnical investigation in the laboratory. This study contributes to ensure the engineering strength of the ground and concluded that the ignorance of substrate conditions may lead to instability or construction failure.

Destructive and nondestructive tests formulation for concrete containing polyolefin fibers

Abstract Polyolefin fiber is a new type of fiber that was used in concrete to improve some of the poor properties of concrete including; tensile strength, ductility, and fracture energy. In this research, the contribution of Polyolefin fiber in improving the properties of hardened concrete was examined by adding polyolefin fibers to mix with different fiber content. The polypropylene fibers were added as a ratio of 0.5, 0.75, 1.0, 1.5, and 2% of concrete volume. Destructive and non-destructive tests were carried out: slump, compression, splitting, and bending, Schmidt Hammer, and ultrasonic pulse velocity tests. The results showed that, as the polyolefin fiber content increases, the workability of concrete reduces dramatically. The experimental findings demonstrate that the concrete tensile strength and ductility were improved by a small improvement in overall compressive strength. The results show that the compressive strength increased gradually with the increase in fiber content of up to 1.5%, and then, the compressive strength starts to decrease. However, the tensile strength increases continuously with the fiber content increasing. A good relationship was obtained between the destructive and nondestructive tests.

Full-Waveform Inversion of Fiber-Optic VSP Data From Deviated Wells

Distributed acoustic sensing (DAS) technology permits measuring the strain or strain rate along a fiber deployed in a well due to seismic wave propagation. In vertical seismic profiling (VSP) acquisitions where seismic waves are excited at the surface and measured by subsurface receivers in the well, the DAS serves as a fast alternative to a conventional geophone array. Like conventional multicomponent VSP velocity measurements, DAS VSP data contain information about the subsurface properties that are encoded in seismic events and attributes such as compressional and shear direct arrivals, reflections, converted modes, multiples, and amplitude and phase variations. These seismic data can be used to obtain elastic properties of the formation and characterize the reservoir. Full-waveform inversion (FWI) extracts the elastic properties of the formation from the seismic wavefield by minimizing the misfit between real measurements and synthetically modeled wavefields. The synthetically generated wavefields are obtained by solving partial differential equations that accurately model the physical phenomena of the real waveforms. For conventional geophone sensors, FWI is formulated for the particle velocity field. In this paper, we present a formulation of the modeling and inversion specifically for DAS measurements as an averaged strain along the fiber. The algorithm does not require converting the data to velocities. The gradient of the misfit function, by adjoint formulation, is a cross correlation in time of the forward-propagated wavefield and backward-propagated residuals injected from the receivers. For conventional sensors, the residuals are injected as force terms, but for DAS data, the residuals are averaged in space first and then injected as moment tensor sources with radiation patterns determined by the well deviation. For multi-offset in-plane and out-of-plane VSP acquisitions, a two-dimensional (2D) algorithm has been developed that inverts for a 2D distribution of elastic medium properties and includes three-dimensional (3D) well deviation effects. This paper will present the results of applying the inversion to real multi-offset, highly out-of-plane VSP fiber data acquired in a deviated well. Simulations confirm that the well trajectory has a considerable impact on the data amplitude and must be included in the modeling and inversion to reproduce amplitude variations. The inverted compressional and shear velocities agree well with the reference model based on sonic data. Another real data example is a multi-offset walk-above acquisition where a targeted domain is located below a deviated portion of the well. The inversion matches reflections and produces an image in the target area.

Sourceless LWD Borehole Acoustics: Field Testing the Concept

Seismic compressional and shear velocities are uniquely sensitive to the elasticity of the Earth and are used to estimate many properties of interest in oil exploration, reservoir development, and production efforts. Such properties include formation lithology, porosity, saturation, mechanical properties, presence of fractures, principal stresses, pore pressure, and formation damage. Logging-while-drilling (LWD) acoustic tools can be used when wireline acoustic logging is prohibitive and/or real-time decisions based on acoustics are needed. It has been shown that modern LWD acoustic tools with powerful, specialized acoustic transmitters can deliver most acoustic data and products with the same quality as their wireline counterparts. However, there is a lot of variation in the quality of traditional LWD acoustic data depending on the tool design. The operator’s decision to run an LWD acoustic tool is not an easy one, though, as the tool is often the most complicated and the longest part of the drillstring. In this paper, we present the field test results of a “sourceless” LWD acoustic tool that uses seismic energy generated by the drill bit to extract formation elastic properties instead of a powerful, specialized transmitter. Such a tool may consist of a receiver section of hydrophones only, which compared with traditional LWD tools, significantly simplifies the mechanical design, shortens the length of the tool, and reduces the tool cost. In the absence of an active transmitter, continuously recording the drill-bit energy as the drill bit rotates enables maximizing the signal-to-noise ratio (SNR) of the formation arrivals. In addition, the presence of azimuthally distributed receiver elements at each receiver axial position permits decomposition of the received wavefield into monopole, dipole, and quadrupole components. Processing results of the sourceless tool using time and frequency semblance are compared to those from a traditional LWD acoustic tool in the same well to demonstrate the viability of the concept. We also demonstrate that, in the case of “traditional” LWD acoustic tools, it is beneficial to place the tool transmitter below the receiver array. In this case, the drill-bit energy propagating in the formation along the borehole is “added” to the energy generated by the source and effectively increases the frequency bandwidth of the source signal and improves the SNR of the resulting formation arrivals.

Fluid Substitution-Based Reservoir Studies and Seismic Response in ‘Vyshion’ Field, Niger Delta

A case study of how fluid substitution affects the seismic waveforms is presented. Direct hydrocarbon prediction on the seismic data is prone to inaccuracy without investigating the impact of fluids on the seismic waveforms since the seismic data is influenced by mineral composition, porosity, salinity, pressure, and other factors in addition to fluid type. The study relies on 3D seismic data and log data gathered from 3 wells. Petrophysical and rock physics models were computed in order to understand the seismic dataset. In the analysis, prolific hydrocarbon intervals were identified. Then, model compressional velocities and densities obtained for various fluid scenarios were generated by using the Gassmann fluid substitution theory. Normalized bulk modulus approach was used to reduce the ambiguities that shales portend on the velocity models. Model synthetics were generated. The synthetic seismograms were compared with the seismic dataset in order to understand how fluid saturation and lithology impacts the seismic data. In the analysis, two major hydrocarbon bearing reservoirs were delineated. Other mapped reservoirs have characteristic indices that make them unsuitable for the fluid modelling. The results show that the model oil velocity model better approximates the field velocity. The density models produced the same kind of results, suggesting that the reservoir fluid is oil. The generated synthetic diagrams show that replacing the in-situ fluid with either gas or oil models has no appreciable impact on the seismic dataset’s amplitude waveform. This is because seismic reflection amplitude only slightly increases each time gas is assumed. By using the seismic data from this field of study, hydrocarbons cannot be directly predicted from amplitude anomalies because the lithology better influences the seismic waveforms than the fluid composition.