Journal of Geophysics and Engineering - Latest Papers

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Influence of prefabricated fissure angle on sandstone damage and infrared radiation temperature characteristics

Fri, 04/13/2018 - 7:00pm
To study the influence of sandstone fissure angle on its characteristics, we performed sandstone uniaxial compression experiments with different prefabricated fissure angles. The infrared radiation temperature (IRT) response characteristics of the prefabricated fissure sandstone and the influences of the fissure angles on mechanical properties, failure modes and infrared radiation indicated the following: (1) the peak stress and failure rate increased as the prefabricated fissure angle increased; the stress peak σ f had a quadratic functional relationship with the prefabricated fissure angle α , and the elastic modulus E was linearly related to the angle of the prefabricated fissure. (2) When0° ≤ α < 45°, the prefabricated fissure tip formed wing cracks that were nearly perpendicular to the prefabricated fissure. When45° ≤ α < 75°, the prefabricated fissure tip formed wing cracks that were nearly parallel to the prefa...

Iterative deblending using the POCS algorithm in the approximate flattened domain

Thu, 04/12/2018 - 7:00pm
We proposed an improved method to eliminate the interference generated by simultaneous-source acquisition, which can help shorten the acquisition period and improve the quality of seismic data. An iterative mathematical framework is devised, which uses the projection onto convex sets algorithm to estimate the blending noise subtracted from the pseudo-deblended data to separate the blended data in an iterative way. Differently to the conventional method using the coherent-promoting operator only based on the curvelet transform, we combine the curvelet transform and the approximate flattened operator (AFO) to improve the deblended result, which can flatten seismic events approximately to preserve the details of useful signals. This is the first time that the AFO and the curvelet transform are combined to enhance the effect of the coherent-promoting operator and improve the performance of deblending. To display the advantages of the improved method, we use both simulated synthetic ...

Use of electromagnetic radiation from fractures for mining-induced stress field assessment

Thu, 04/12/2018 - 7:00pm
This paper presents an electromagnetic radiation-based method to qualitatively assess mine-induced stress field at the longwall face. We first analyze the correlation between electromagnetic (EM) signals and stress, and then measure the signals and drilling bits in both the strike and dip directions at the 11702 working face of Nuodong Coal Mine, China, which indirectly verifies this method. Results show that there is a positive correlation between EM intensity and stress. In the same coal seam, the frequency of EM signals is inversely proportional to the extended size of the cracks inside the coal rock, and the dominant frequency (DF) of the EM signal is negatively related to external stress. Test results in Nuodong Coal Mine show that the EM intensity and DF can well reflect a stress relief zone, concentration zone and original zone. In addition, through field test and theoretical calculation, we can ascertain that the crack propagation length is from several centimeters to gr...

Wavelet threshold de-noising of rock acoustic emission signals subjected to dynamic loads

Thu, 04/12/2018 - 7:00pm
The discrete wavelet transform theory was used to process non-stationary rock acoustic emission signals recorded in split Hopkinson pressure bar tests. Wavelet basis db10 was selected as the optimum wavelet for processing such signals by calculating the reconstruction root mean square error (RMSE) of each wavelet basis candidate, and the unbiased estimation procedure SURE was used to determine the threshold value for each decomposition level. Denoising by wavelet thresholding and conventional low-pass filter were compared by evaluating the signal to noise ratio and RMSE. Results show that discrete wavelet transform has a favorable denoising effect and better signal reconstruction capability, and also indicate that the wavelet technique is especially suitable for denoising non-stationary signals like the transient signals of rock acoustic emission under impact loading.

Characteristics and generation mechanism of ULF magnetic signals during coal deformation under uniaxial compression

Thu, 04/12/2018 - 7:00pm
Low-frequency magnetic signals with the advantages of fewer interfering factors and longer propagation ranges are more useful for improving the accuracy of monitoring and early warning technology for coal or rock dynamic disasters. In this paper, the characteristics of low-frequency magnetic signals generated during uniaxial compression failure of coal are investigated in the time and frequency domain. The generation mechanism of low-frequency magnetic signals is proposed based on the correlation between low-frequency magnetic signals and micro-seismic signals. The experimental results show that (1) abnormal ultra-low-frequency (ULF) magnetic signals can be clearly observed in the process of coal failure. The signals occur as oscillating pulses, with amplitudes between 13 and 156 nT. (2) Both the maximum amplitude and energy of the signals are both positively correlated with the strength of samples and loading speed. (3) Signals in the direction perpendicular to the crack surfac...

Evaluation of the pore structure of tight sandstone reservoirs based on multifractal analysis: a case study from the Kepingtage Formation in the Shuntuoguole uplift, Tarim Basin, NW China

Thu, 04/12/2018 - 7:00pm
Both the microscopic pores and the pore structure of a reservoir affect its properties, including permeability and the distribution of oil and gas. Due to the stronger pore structure heterogeneity in tight sandstone reservoirs, it is difficult to characterize the pore structure of tight sandstone with traditional Euclidean geometry. In this study, based on the comprehensive utilization of reservoir data, such as petrophysical property data, mercury injection capillary pressure data and thin sections images, image processing and multifractal analyses are used to classify and describe the pore structure of tight sandstone in the Kepingtage Formation in the Shuntuoguole low uplift, Tarim Basin. The relationships among pore structure parameters, physical properties, and multifractal feature parameters are discussed in detail. Finally, a pore structure classification method using multifractal parameters based on K-means clustering analysis is proposed and applied to tight sandstone. ...

Drilling rate prediction from petrophysical logs and mud logging data using an optimized multilayer perceptron neural network

Thu, 04/12/2018 - 7:00pm
Rate of penetration (ROP) enhancement serves as a key factor in reducing drilling time and hence drilling costs. ROP enhancement requires identification of the parameters affecting this rate. However, the large number of effective parameters, which are further immersed in noise, makes it difficult to present a highly accurate and comprehensive model. In the present research, in order to predict the drilling ROP in one of the vertical wells drilled into the Karanj Oilfield, a hybrid model composed of a multilayer perceptron (MLP) neural network together with either a particle swarm optimization (PSO) algorithm or a cuckoo optimization algorithm (COA) was used. For this purpose, first petrophysical logs and drilling data were denoised using the Savitzky–Golay filter. Then, the ‘plus- l -take- r ’ method was used to select superior features. Feature selection results indicated that an increase in the number of input parameters tends to reduce the error associated with the...

Joint velocity updating for anisotropic PP and PS prestack time migration based on hyperbolic correction of nonhyperbolic moveout

Thu, 04/12/2018 - 7:00pm
The analysis of anisotropic velocity has been well researched to support multicomponent seismic migration of anisotropic media. Because of anisotropy and asymmetric ray paths, PS-wave reflection moveout is more nonhyperbolic than PP-wave reflection moveout, which makes conventional root-mean-square velocity analysis no longer applicable. Hence, additional work is needed to reform the existing seismic data processing software or to develop new velocity analysis modules. For this reason, we propose a method of joint anisotropic velocity updating for PP and PS prestack time migration based on the hyperbolic correction of nonhyperbolic moveout. Our velocity analysis method can be performed using conventional velocity analysis. According to the PP-wave moveout equation in VTI media, we derive an accurate double-square-root moveout equation for PS-waves, which is then used to generate PP and PS common-imaging-point gathers. The travel time and offset of each sample are maintained when...

Prediction of total organic carbon content in shale reservoir based on a new integrated hybrid neural network and conventional well logging curves

Wed, 03/21/2018 - 8:00pm
There is increasing interest in shale gas reservoirs due to their abundant reserves. As a key evaluation criterion, the total organic carbon content (TOC) of the reservoirs can reflect its hydrocarbon generation potential. The existing TOC calculation model is not very accurate and there is still the possibility for improvement. In this paper, an integrated hybrid neural network (IHNN) model is proposed for predicting the TOC. This is based on the fact that the TOC information on the low TOC reservoir, where the TOC is easy to evaluate, comes from a prediction problem, which is the inherent problem of the existing algorithm. By comparing the prediction models established in 132 rock samples in the shale gas reservoir within the Jiaoshiba area, it can be seen that the accuracy of the proposed IHNN model is much higher than that of the other prediction models. The mean square error of the samples, which were not joined to the established models, was reduced from 0.586 to 0.442. Th...

Metaheuristic optimization approaches to predict shear-wave velocity from conventional well logs in sandstone and carbonate case studies

Wed, 03/21/2018 - 8:00pm
Seismic wave velocities, along with petrophysical data, provide valuable information during the exploration and development stages of oil and gas fields. The compressional-wave velocity ( V P ) is acquired using conventional acoustic logging tools in many drilled wells. But the shear-wave velocity ( V S ) is recorded using advanced logging tools only in a limited number of wells, mainly because of the high operational costs. In addition, laboratory measurements of seismic velocities on core samples are expensive and time consuming. So, alternative methods are often used to estimate V S . Heretofore, several empirical correlations that predict V S by using well logging measurements and petrophysical data such as V P , porosity and density are proposed. However, these empirical relations can only be used in limited cases. The use of intelligent systems and optimization algorithms are inexpensive, f...

Scaling of counter-current imbibition recovery curves using artificial neural networks

Wed, 03/21/2018 - 8:00pm
Scaling imbibition curves are of great importance in the characterization and simulation of oil production from naturally fractured reservoirs. Different parameters such as matrix porosity and permeability, oil and water viscosities, matrix dimensions, and oil/water interfacial tensions have an effective on the imbibition process. Studies on the scaling imbibition curves along with the consideration of different assumptions have resulted in various scaling equations. In this work, using an artificial neural network (ANN) method, a novel technique is presented for scaling imbibition recovery curves, which can be used for scaling the experimental and field-scale imbibition cases. The imbibition recovery curves for training and testing the neural network were gathered through the simulation of different scenarios using a commercial reservoir simulator. In this ANN-based method, six parameters were assumed to have an effect on the imbibition process and were considered as the inputs...

An improved method for predicting brittleness of rocks via well logs in tight oil reservoirs

Wed, 03/21/2018 - 8:00pm
There can be no industrial oil production in tight oil reservoirs until fracturing is undertaken. Under such conditions, the brittleness of the rocks is a very important factor. However, it has so far been difficult to predict. In this paper, the selected study area is the tight oil reservoirs in Lucaogou formation, Permian, Jimusaer sag, Junggar basin. According to the transformation of dynamic and static rock mechanics parameters and the correction of confining pressure, an improved method is proposed for quantitatively predicting the brittleness of rocks via well logs in tight oil reservoirs. First, 19 typical tight oil core samples are selected in the study area. Their static Young’s modulus, static Poisson’s ratio and petrophysical parameters are measured. In addition, the static brittleness indices of four other tight oil cores are measured under different confining pressure conditions. Second, the dynamic Young’s modulus, Poisson’s ratio and brittleness index are calculat...

Time-domain full waveform inversion using instantaneous phase information with damping

Wed, 03/21/2018 - 8:00pm
In time domain, the instantaneous phase can be obtained from the complex seismic trace using Hilbert transform. The instantaneous phase information has great potential in overcoming the local minima problem and improving the result of full waveform inversion. However, the phase wrapping problem, which comes from numerical calculation, prevents its application. In order to avoid the phase wrapping problem, we choose to use the exponential phase combined with the damping method, which gives instantaneous phase-based multi-stage inversion. We construct the objective functions based on the exponential instantaneous phase, and also derive the corresponding gradient operators. Conventional full waveform inversion and the instantaneous phase-based inversion are compared with numerical examples, which indicates that in the case without low frequency information in seismic data, our method is an effective and efficient approach for initial model construction for full waveform inversion.<...

A novel design for storage of inner stress by colloidal processing on rock-like materials

Wed, 03/21/2018 - 8:00pm
Inner stress exists in rocks, affecting rock engineering, yet has received very little attention and quantitative investigation because of uncertainty about its characteristics. Previous studies have suggested that the inner stresses of rock materials are closely related to their physical state variation. In this work, a novel mold was designed to simulate the storage process of inner stress in specimens composed of quartz sands and epoxy. Then, thermal tests were carried out to change the physical state of the specimens, and expansion of the specimens was monitored. The results indicated that inner stress could be partly locked by the mold and it could also be released by heating. It can be inferred from the analysis that one necessary condition of storage and release of inner stress is physical state variation. Additionally, by using an XRD method, the variations in the interplanar spacing of the quartz sands were detected, and the results reflect that inner stress could be lo...

A new scheme for velocity analysis and imaging of diffractions

Wed, 03/21/2018 - 8:00pm
Seismic diffractions are the responses of small-scale inhomogeneities or discontinuous geological features, which play a vital role in the exploitation and development of oil and gas reservoirs. However, diffractions are generally ignored and considered as interference noise in conventional data processing. In this paper, a new scheme for velocity analysis and imaging of seismic diffractions is proposed. Two steps compose of this scheme in our application. First, the plane-wave destruction method is used to separate diffractions from specular reflections in the prestack domain. Second, in order to accurately estimate migration velocity of the diffractions, the time-domain dip-angle gathers are derived from a Kirchhoff-based angle prestack time migration using separated diffractions. Diffraction events appear flat in the dip-angle gathers when imaged above the diffraction point with selected accurate migration velocity for diffractions. The selected migration velocity helps to pr...

Crack propagation and coalescence due to dual non-penetrating surface flaws and their effect on the strength of rock-like material

Mon, 03/12/2018 - 8:00pm
Non-penetrating surface flaws play a key role in the fracture process of rock-like material, and could cause localized collapse and even failure of the materials. Until now, the mechanism and the effect of surface crack propagation have remained unclear. In this paper, compression tests on gypsum (a soft rock material) are conducted to investigate crack propagation and coalescence due to non-penetrating surface flaws and their effect on the material strength. Specimens are tested under dual pre-existing surface flaws with various combinations of depth and spacing. The results show that when the pre-existing flaws are non-penetrating, the d / t ratio (flaw depth ratio, d is the pre-existing flaw cutting depth and t is the specimen thickness) and the spacing (the distance between the two flaw internal tips) have a strong influence on surface crack patterns and specimen strength. Few cracks emanate from the pre-existing flaws when the flaw depth ratio is e...

Seismic instantaneous frequency extraction based on the SST-MAW

Mon, 03/12/2018 - 8:00pm
The instantaneous frequency (IF) extraction of seismic data has been widely applied to seismic exploration for decades, such as detecting seismic absorption and characterizing depositional thicknesses. Based on the complex-trace analysis, the Hilbert transform (HT) can extract the IF directly, which is a traditional method and susceptible to noise. In this paper, a robust approach based on the synchrosqueezing transform (SST) is proposed to extract the IF from seismic data. In this process, a novel analytical wavelet is developed and chosen as the basic wavelet, which is called the modified analytical wavelet (MAW) and comes from the three parameter wavelet. After transforming the seismic signal into a sparse time–frequency domain via the SST taking the MAW (SST-MAW), an adaptive threshold is introduced to improve the noise immunity and accuracy of the IF extraction in a noisy environment. Note that the SST-MAW reconstructs a complex trace to extract seismic IF. To demonstrate t...

Generalized analytic solutions and response characteristics of magnetotelluric fields on anisotropic infinite faults

Mon, 03/12/2018 - 8:00pm
In order to understand directly and analyze accurately the detected magnetotelluric (MT) data on anisotropic infinite faults, two-dimensional partial differential equations of MT fields are used to establish a model of anisotropic infinite faults using the Fourier transform method. A multi-fault model is developed to expand the one-fault model. The transverse electric mode and transverse magnetic mode analytic solutions are derived using two-infinite-fault models. The infinite integral terms of the quasi-analytic solutions are discussed. The dual-fault model is computed using the finite element method to verify the correctness of the solutions. The MT responses of isotropic and anisotropic media are calculated to analyze the response functions by different anisotropic conductivity structures. The thickness and conductivity of the media, influencing MT responses, are discussed. The analytic principles are also given. The analysis results are significant to how MT responses are pe...

Identifying the morphologies of gas hydrate distribution using P-wave velocity and density: a test from the GMGS2 expedition in the South China Sea

Mon, 03/12/2018 - 8:00pm
Pore-filling and fracture-filling are two basic distribution morphologies of gas hydrates in nature. A clear knowledge of gas hydrate morphology is important for better resource evaluation and exploitation. Improper exploitation may cause seafloor instability and exacerbate the greenhouse effect. To identify the gas hydrate morphologies in sediments, we made a thorough analysis of the characteristics of gas hydrate bearing sediments (GHBS) based on rock physics modeling. With the accumulation of gas hydrate in sediments, both the velocities of two types of GHBS increase, and their densities decrease. Therefore, these two morphologies cannot be differentiated only by velocity or density. After a series of tests, we found the attribute ##IMG## [] {$\rho {{V}_{{\rm{P}}}}^{0.5}$} as a function of hydrate concentration show opposite trends for these two morphologies due to their different formation m...

Full waveform seismic AVAZ signatures of anisotropic shales by integrated rock physics and the reflectivity method

Mon, 03/12/2018 - 8:00pm
A set of parallel vertical fractures embedded in a vertically transverse isotropy (VTI) background leads to orthorhombic anisotropy and corresponding azimuthal seismic responses. We conducted seismic modeling of full waveform amplitude variations versus azimuth (AVAZ) responses of anisotropic shale by integrating a rock physics model and a reflectivity method. The results indicate that the azimuthal variation of P -wave velocity tends to be more complicated for orthorhombic medium compared to the horizontally transverse isotropy (HTI) case, especially at high polar angles. Correspondingly, for the HTI layer in the theoretical model, the short axis of the azimuthal PP amplitudes at the top interface is parallel to the fracture strike, while the long axis at the bottom reflection directs the fracture strike. In contrast, the orthorhombic layer in the theoretical model shows distinct AVAZ responses in terms of PP reflections. Nevertheless, the azimuthal signatur...