Journal of Geophysics and Engineering - Latest Papers

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Study on energy band characteristic of microseismic signals in water inrush channel

Mon, 06/04/2018 - 7:00pm
In this paper the mechanism of water inrush disaster is analyzed, and the correlation between the evolution law of water inrush channel and microseismic (MS) monitoring in prevention structure is established. The main MS events include water and rock mass impact, filling and rock impact in the water inrush channel. The idea of positioning the water inrush channel is presented by analyzing the filling and rock impact MS signal. A large model test restores the environment of various water inrush channels. The MS technique is used to monitor the water inrush channels in the test. Wavelet packet theory is used to decompose the MS signals of water inrush channel. The result indicates that the background noise frequency is 0–1 kHz and the effective signal frequency range is above 1250 Hz. The paper statistically analyzes the MS energy in the different water inrush channels. The result indicates that the shape of water inrush channel has little influence on the energy. It is concluded ...

Similar constructive method for solving the model of coalbed methane flow through coalbed methane reservoirs

Mon, 05/28/2018 - 7:00pm
Coalbed methane (CBM) is produced through desorption, diffusion, and seepage processes. However, pressure during CBM production, especially the seepage process, is a very complicated problem. Methods for solving the pressure models for CBM reservoirs are multidisciplinary and rather sophisticated. In this paper, an elementary and simple method for solving the CBM seepage model is proposed. First, a classical seepage model was built to study CBM seepage at a variable flow rate. After the transformation of pressure into pseudo-pressure and dimensionless treatments, a definite problem for the CBM seepage model was obtained. By Laplace transformation, the definite problem can be solved as a boundary value problem in Laplace space. Then, this boundary value problem was solved by the proposed method which is elementary and simple and its solutions have a structure similar to that of a continued fraction. This explains why this method is called the similar constructive method. With thi...

Experimental and numerical investigations on the vertical propagation of hydraulic fractures in laminated shales

Tue, 05/22/2018 - 7:00pm
Bedding structure and strong tectonic compression of deep shale reservoirs have a great influence on the vertical propagation of hydraulic fractures and proppant transportation, posing a severe challenge for the hydraulic fracturing design. A combined experimental and numerical study was carried out to investigate the vertical propagation of hydraulic fractures in laminated shales. As a supplement to the physical experiment method, a flow-stress-displacement-damage coupling method based on continuum mechanics was developed, which can effectively simulate complex hydraulic fracture geometries observed in mining experiments. The validity of the numerical method was verified by experiment results. The experiment and simulation results show that: (1) strong horizontal tectonic compression is not favorable for hydraulic fractures to pass through bedding planes; (2) the decrease of bedding interface strength and increase of bedding dip angle will cause hydraulic fracture diversion, of...

An improved frequency-domain algorithm for stable reduction to the pole at low latitudes

Tue, 05/22/2018 - 7:00pm
Based on a modification of the routine of the reduction-to-the-pole (RTP) operator in the frequency domain, the approaches of local suppression and global suppression perform well in suppressing the unstable amplification zone for low-latitude RTP. However, additional parameters are inevitably introduced whose values exert a direct effect on the accuracy of the RTP. In this paper, these introduced parameters are optimized by calculating the correlation coefficient between the RTP results and the normalized source strength (NSS), then the RTP results under the optimal parameters can be obtained. Furthermore, an improved regularization algorithm is proposed and applied to the optimized operators to resolve the problem of the high-frequency amplification effect existing in these operators. The results of a simulation and principal verification experiment prove that the proposed method cannot only taper off the high-frequency noise in the original signal but also improve the stabili...

Application of flow zone indicator and Leverett J-function to characterise carbonate reservoir and calculate precise water saturation in the Kujung formation, North East Java Basin

Tue, 05/22/2018 - 7:00pm
Carbonate reservoirs are known as heterogeneous reservoirs due to their pore complexity caused by depositional setting and diagenetic process. This complexity can create comprehension about storage capacity and flow capacity, including water saturation. A reservoir characterisation method using a flow zone indicator (FZI) can be useful to divide reservoir rock based on its flow unit, as well as irreducible water saturation. Reservoir characterisation is applied to the Kujung formation, in Jago and the Bravo Structure, North East Java Basin which has an invalid calculation of Archie’s water saturation. First, the flow unit is identified by FZI, then the water saturation of the reservoir is calculated by the Leverett J-Function method for which every flow unit has its irreducible water saturation. From the FZI method, the Kujung formation can be divided into three flow units with their own characteristics. Flow unit 1 has a channelling pore type and a 0.25 Swirr value, flow unit 2...

Coupled thermal−gas−mechanical (TGM) model of tight sandstone gas wells

Tue, 05/22/2018 - 7:00pm
The mechanism of CO 2 fracturing under coupled thermal−gas−mechanical (TGM) conditions is important for gas production in tight sandstone gas wells. In this study, a coupled TGM model was proposed on the basis of the elastic damage principal, and the coupling relationships were expressed by the governing equations. The proposed model was then tested through comparison between the numerical uniaxial compressive test and the laboratory test. COMSOL MULTIPHYSICS was adopted to calculate the coupled numerical model; the impact of injection rate and injection gas temperature was fully investigated. The research results showed that the initiation pressure stayed stable with the increase of the breakdown pressure and injection rate over a certain range (0.106 m 3 s −1 –0.848 m 3 s −1 ). The seepage area under the injection rate of 0.848 m 3 s −1 was 3.45 times that under the injection rate of 0.106 m 3 s ...

Moho depth of the northern Vietnam and Gulf of Tonkin from 3D inverse interpretation of gravity anomaly data

Tue, 05/15/2018 - 7:00pm
In this paper, the authors present the result of three-dimensional (3D) direct inversion of gravity data to determine the Moho depth along the Red River Fault (RRF) zone and adjacent areas in the land territory of Vietnam and the Gulf of Tonkin. The Moho depth was calculated by 3D Parker inversion supplemented with the gravity anomaly power density spectrum. The given Moho depth and the available teleseismic and magnetotelluric Moho depth are well matched. A structural Moho map of the study region was constructed from the interpretation results. The Moho surface was uplifted along the RRF zone. The shallowest Moho depth was determined in the Red River Basin (RRB), where it ranges from 22 ± 1.0 km to 24 ± 1.0 km in the depocenter of the RRB in the Gulf of Tonkin to 27 ± 1.0 km to 29 ± 1.0 km in the Red River Delta. It is 29 ± 1.0 km to 32 ± 1.0 km from Vietri to Laocai provinces. The deepest Moho depth was found in the northwesternmost and northernmost land territory of Vietnam, ...

Adaptive rank-reduction method for seismic data reconstruction

Tue, 05/15/2018 - 7:00pm
Seismic data reconstruction plays an important role in the whole seismic data processing and imaging workflow, especially for those data that are acquired from severe field environment and are missing a large portion of the reflection signals. The rank-reduction method is considered to be a very effective method for interpolating data that are of small curvature, e.g. the post-stack data. However, when the data are more complicated, the rank-reduction method may fail to achieve acceptable performance. A useful strategy is to use local windows to process the data so that the data in each local window satisfy the plane-wave assumption of the rank-reduction method. However, the rank in each window requires a careful selection. Traditional methods select a global rank for all windows. We have proposed an automatic algorithm to select the rank in each processing window. The energy ratio between two consecutive singular values is chosen as the criterion to define the optimal rank. We ...

A frequency-domain element-free method for seismic modeling and reverse-time migration

Tue, 05/15/2018 - 7:00pm
In this paper, a frequency-domain element-free method (EFM) for seismic modeling and reverse-time migration is presented. The application of time-domain EFM has been demonstrated successfully in seismic data processing and its advantages are shown. The absence of elements makes the EFM more flexible than the finite element method and it can be applied to more complex problems such as for irregular surfaces. Because of the utilization of the moving-least-squares fitting method, the dependent variable and its derivative are both continuous and precise in EFM. However, the large computation time of time-domain EFM limits its usefulness. We have developed an algorithm for frequency-domain EFM that reduces its computation time. Unlike time-domain propagators, the developed algorithm solves array equations to calculate a single-frequency wavefield. Without time iteration, there is very little accumulated error and, because of the spectrum of the source, we only need to calculate parts...

Micro- and macroscopic study of crack propagation in coal: theoretical and experimental results and engineering practice

Tue, 05/15/2018 - 7:00pm
Coal is a material that fractures naturally. To determine the physical laws that govern crack propagation in coal, a fracture mechanics model was established and uniaxial compression experiments were conducted on coal samples. During the experiments, a high-definition camera, scanning electronic microscope and an optical microscope were used to record the crack propagation process. These techniques illustrate an intuitive procession of events: damage → crack → crack propagation → macroscopic failure. Pre-existing and induced fractures were studied separately, and results show that induced fractures are formed by the evolution of damage and always occur near these pre-existing cracks where the damage is severe. In a complete stress–strain curve a bending point exists after which transverse induced cracks begin to develop. The pre-existing crack experiences shear slip, Mode II propagation and stable bending propagation before the plastic point after which it switches to shear prop...

Seismic data analysis using synchrosqueezing short time Fourier transform

Tue, 05/15/2018 - 7:00pm
The synchrosqueezing wavelet transform (SWT) reallocates the wavelet transform values to different points, hence produces a sharp spectral decomposition for the input signal. The SWT method was widely used for de-noising, spectral decomposition, etc. In this paper, a new synchrosqueezing method was proposed based on short time Fourier transform. The proposed method reassigns the short time Fourier transform values to different points, thus produces a concentrated time–frequency map. Furthermore, the proposed method has an inverse formula, which allows the reconstruction of the input signal from its spectral decomposition. Examples showed that the proposed method is effective for revealing the time–frequency characterizations of non-stationary signals.

Fractional-order stability analysis of earthquake dynamics

Tue, 05/15/2018 - 7:00pm
Fractional calculus is suitable for systems with memory and for fractal systems. Earthquakes have both properties. It is fair to claim that a fractional model is very efficient for earthquake modeling. Our study is focused on the effects of the fractional-order derivative on the ‘train model’ of Burridge–Knopoff. We note that these effects introduce additional degrees of freedom. Contrary to the integer model in which the fault remains seismologically active, the fractional derivative causes the transition from stick–slip oscillation to a stable equilibrium state. It is shown that the motion along the fault could be suppressed or reduced to an aseismic creeping when the fractional-order decreases. In the fractional model, we establish that the magnitude of the earthquake strongly depends on the fractional-order derivative. The stability of the stationary state is studied using fractional stability theory and the obtained results exhibit the powerful dependance of this stability ...

Influence of diffraction effects on attenuation measurement using pulse transmission method

Wed, 05/09/2018 - 7:00pm
Ultrasonic attenuation measurement is widely used in nondestructive testing, medical, geophysical and other fields. Diffraction effects, the main influencing factor in ultrasonic attenuation measurement, have been studied in detail in the field of acoustics and nondestructive testing, but the diffraction effects on attenuation measurement, especially Q estimation, are rarely explored in geophysical fields. In this paper, the influence of diffraction effects under different test conditions are simulated based on the formula for radiated elastic wave fields. The relative errors caused by diffraction effects are calculated using the simulation results. Based on the pulse transmission method, the diffraction effects on the measurement of attenuation under different test conditions were studied using standard samples. The experimental results were compared with the simulation results. The sensitivity of the diffraction effects to the attenuation measurement of different attenu...

Movement and failure law of slope and overlying strata during underground mining

Wed, 05/09/2018 - 7:00pm
Overburden deformation has a considerable influence on slope stability during underground mining works. A simulation experiment for underground mining is performed in this study. The movement of the overlying strata caused by mining during the mining process is observed using a three-dimensional optical displacement monitoring system. Based on the simulation experiment results, a particle contact-based meshfree method (PCMM) is proposed. The elastoplastic analysis and sliding process simulation of the slope are realized by introducing the softening Mohr–Coulomb model and maximal tensile stress model into continuous media elements. The deformation process and slope failure are analyzed by using the PCMM numerical simulation method. The results showed that the overburden gradually degraded as the work face continuously pushed forward. Furthermore, the basic roof bore the force generated by the upper rock mass. Hence, a ‘rock beam’ force distribution developed. The farther the dist...

An improved analytical model for low-salinity waterflooding

Wed, 05/09/2018 - 7:00pm
Low-salinity waterflooding (LSW) is popular in the oil industry worldwide due to its improved enhanced oil recovery performance, simple operation and environmental protection. However, the mechanisms underlying LSW are still being debated. To construct an analytical model which can interpret the LSW mechanism has been a big challenge. In this paper, we will combine several mechanisms to construct an analytical model and obtain a solution for LSW. After excellent validation with the experimental data, we propose several conclusions based on our model: (1) LSW can increase oil recovery and slow down the breakthrough of water at the beginning of field development and after conventional waterflooding ; (2) the injection velocity of low-salinity water should be controlled within the proposed range in order for the clay cake to form. For a reservoir with a larger porosity, it is easier to operate the injection velocity; (3) lower salinity will lead to a higher water recovery factor du...

Pressure and pressure derivative interpretation for horizontal wells in compressible formations

Wed, 05/09/2018 - 7:00pm
A methodology for horizontal well test interpretation in both compressible and bounded or infinite unconsolidated reservoirs with a single fluid is presented. Algebraic expressions are developed from characteristic points and lines found on the log–log plot the pressure and pressure derivative versus time log–log plot, to determine horizontal permeability, well-drainage area and permeability modulus were developed for the two external boundary condition cases dealt with. The results obtained from the developed equations provided good results as they are demonstrated by the application to synthetic examples.

New evidence from shallow seismic surveys for Quaternary activity of the Benchahe fault

Wed, 05/09/2018 - 7:00pm
In order to redefine the activity of the Benchahe fault, according to target layers with different burial depths, we followed the work rationale of ‘from known to unknown, from deep to shallow and step by step’. We adopted not only the multi-level seismic detection method but also the joint exploration of P- and SH-waves. We obtained high-resolution images of the stratum structure in the depth range from 1350 m to near the surface and clear image results of the Benchahe fault. This exploration research accurately locates the Benchahe fault, and further shows that it is not a single fault but rather a fault-terrace belt consisting of two N-dipping faults within the effective detection depth. We clarify that the up-breakpoint of the southern section (F 1−1 ) of the Benchahe fault is shallower and more active. The Benchahe fault is a near EW-trending fault, dipping north with an apparent dip angle of around 60°–75°. Subsequently, through geologic borehole section verificat...

Analysis of time-lapse seismic and production data for reservoir model classification and assessment

Wed, 05/09/2018 - 7:00pm
The heterogeneous distribution of reservoir properties is one of the most important uncertainties in static and dynamic reservoir modelling. Petrophysical properties are usually interpolated within reservoir models from sparse well-log data, which can lead to highly uncertain estimates at inter-well locations that directly affect the reliability of fluid-flow model predictions of reservoir behaviour. To address this issue, one approach is to build an ensemble of equiprobable models that combine different geostatistical realisations of reservoir properties that ideally span the range of potential outcomes. While this process captures the impact of reservoir property distributions on the model response, a major challenge is classifying the subset of models in the ensemble best representing reservoir fluid-flow behaviour. Time-lapse seismic attributes are useful for reducing such uncertainties, since they image fluid-movement trends that provide insights regarding fault locations a...

Improved energy balance theory applied to roadway support design in deep mining

Wed, 05/09/2018 - 7:00pm
Deep mining excavations are challenging, especially because roadways are subject to increasingly high stresses and large deformations. In particular, effective support patterns are required to prevent failures associated with deep mining. The conventional energy balance theory cannot be directly applied for roadway support design in deep mining. In this paper, assumptions were made to improve the energy balance theory, where a semi-circular roof roadway experiencing geostatic stresses was analyzed under plane strain conditions and its failure was identified by the Hoek–Brown failure criterion. An improved energy balance theory was proposed to solve the problem, where the released energy in the plastic zone of the roadway was supposed to be less than the maximum absorbed energy of the supporting structures. The optimized roadway support pattern and parameters for deep mining were then determined through elastic mechanics and complex analysis. The efficacy of the proposed method w...

A new fracture detection method based on full-azimuth anisotropic migration and shaping regularization

Wed, 05/09/2018 - 7:00pm
Fracture detection plays an important role in oil and gas exploration. Azimuth-dependent amplitude anisotropy is a key indicator for fracture characterization. In order to not only retain the azimuthal information but also preserve the genuine amplitude relationships in the common image gathers, an accurate anisotropic migration algorithm is required. A further complication arises when the migrated seismic data are inverted to determine the fracture properties, specifically the challenge posed by the stability of the Rüger equations. In this paper, we derive a fourth-order travel time equation for orthorhombic media that performs the anisotropic migration in the local angle domain. By introducing a new shaping regulator to the conventional fracture inverse problem, we improved the accuracy and convergence of the algorithm. The proposed migration and inversion approaches have been validated with a synthetic and a real dataset from the Tarim basin. The results of this validation s...