Table of contents

Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1–100 Hz) dispersion maxima appear at ∼5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity (V_p) dispersion is estimated ∼5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on the angle dependent seismic migrated sections is carried out by inverting spectrally decomposed isofrequency sections using a least squares algorithm. The inverted results show that the top of the reservoir is more clearly demarcated at low frequency (∼7 Hz) than at higher frequencies.

In a recent paper, seismic amplitude-variation-with-offset (AVO) equations describing P-to-P and P-to-S reflections from boundaries separating low-loss viscoelastic media, taking into account variations in the attenuation angle, have been derived. We find that opportunities now present themselves to use these equations to expose a range of relationships between measured amplitudes and subsurface elastic and anelastic properties. This has significant applicability in the quantitative interpretation of seismic data in, for instance, reservoir characterization. To facilitate the analysis, we decompose the equations into three parts: elastic, homogeneous and inhomogeneous. We show that, for PP modes, the elastic part is sensitive to changes across a reflecting boundary in density and P- and S-wave velocities; the homogeneous part is sensitive to changes in density, S-wave velocity and the P- and S-wave quality factors; and the inhomogeneous part is sensitive to changes in density, and P-and S-wave velocities. The latter term is seen to vanish when the attenuation angle vanishes. For PP modes, elastic and homogeneous terms are linear with respect to ${\sin }^{2}{\theta }_{{\rm{P}}}$, where ${\theta }_{{\rm{P}}}$ is the P-wave incidence angle; however, the inhomogeneous term is similarly linear only if normalized by dividing by tan θ_P. For PS modes, the elastic part is sensitive to changes in density and S-wave velocity; the homogeneous part is sensitive to changes in density, S-wave velocity and the S-wave quality factor; and the inhomogeneous part is sensitive to changes in density and S-wave velocity. This term also vanishes for the zero attenuation angle, i.e. in the homogenous limit. For PS modes, the inhomogeneous terms are linear with respect to ${\sin }^{2}{\theta }_{{\rm{P}}}$; however the elastic and homogeneous terms are first and third order in $\sin {\theta }_{{\rm{P}}}$. A further and key result of this expansion of the wave types allowable in AVO analysis is that, for inhomogeneous PS scattering, the viscoelastic AVO equations predict a non-zero reflectivity at normal incidence. This is a significant deviation from common models of converted wave amplitude analysis.

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 that the signals' energy is dominant at low frequency and the effective signals' energy is weak. An improved scheme is proposed for monitoring the water inrush against traditional MS technology based on the above conclusions. The wavelet packet theory can be embedded to filter low frequency signals in software, and the sampling frequency shall be no less than 2500 Hz and the monitoring frequency of the sensor shall be no less than 1250 Hz in hardware. In this paper, wavelet packet decomposition and energy theory are used to analyze the MS signals of water inrush channels, and the preliminary identification of MS waveforms in water inrush channels is realized, which provides an idea for monitoring water inrush disaster in underground works.

Significant discontinuities exist in the production data of many unconventional reservoirs, which always causes difficulties in production data analysis (PDA). This paper proposes a PDA method to address the problem caused by the significant discontinuities based on the virtual equivalent time, which is calculated by using the average formation pressure. With the virtual equivalent time, production data with significant discontinuities are converted into several interconnected segments, and new type curves are then generated and applied to PDA, which improves the fitting precision of the production data. With the improved fitting results, accurate productivity forecasting can be achieved. A field case study is carried out, comparing the new method with commercial software. The results show that the new method has better fitting results, and that the errors caused by significant discontinuities are effectively eliminated. The effectiveness of the proposed method is further verified by the comparison between the forecasting data and the field data. The method proposed in this paper can improve the precision of the interpreted parameters, which is beneficial to the more reliable and efficient prediction of well production performance.

Wave peak particle velocity (PPV) is an index often used internationally to determine the structural damage caused by mining blasts. Since detailed spatial variations due to local soil effects are ignored in empirical PPV equations, new artificial intelligence (AI) methods have become a proper tool for describing the local effect of wave propagation in complex areas. An artificial neural network (ANN) has been developed in this work to overcome traditional empirical method limitations. Data collected from several seismic stations strategically located within a pilot study area, where two controlled explosions were designed and detonated exclusively for this research, were used to train an ANN model and a non-linear regression (NLR) model. The goodness of fit of the two methods applied in this research, as well as the spatial variation of the site effects, were analyzed. Results showed that the ANN model has a high capacity to adapt to the local soil effects, overcoming the problems related to regression traditional methods and offering new lights for understanding the soil and topographic amplification phenomenon.

The characterization of carbonate reservoirs based on seismic and acoustic log data is difficult due to their anisotropy. Complex pore structures are one of the major factors causing this anisotropy. To solve this issue, a model considering pore structure is proposed. In this model, the differential Kuster–Toksöz model and Hudson's model are used to add various types of pores in the rock matrix, and Thomsen's anisotropy theory is used to estimate the anisotropic velocities of carbonate rocks with fractures of arbitrary dips. Based on this model, the effects of pore structure (including porosity, pore aspect ratio, fracture porosity and dip) on elastic wave velocities are discussed. The simulation results show that the pore aspect ratio and porosity are the dominant factors influencing the elastic wave velocities of carbonates. Pores with small aspect ratios (aspect ratios of less than 0.15) have an extremely significant influence on elastic wave velocities. For anisotropic carbonates with aligned fractures, fracture porosity and dip are important factors influencing elastic wave velocities, especially when they exceed critical values. The critical values for P- and S-waves are 0.3% and 30° and 0.3% and 20°, respectively. These rules provide good guidance for analysing the measured data and are helpful for characterizing carbonate reservoirs and optimizing production. The elastic wave velocities predicted by this model agree well with acoustic well log data in fractured-vuggy carbonate rocks with arbitrary dip fractures. This result demonstrates that the proposed model is valid for predicting anisotropic velocities in fractured-vuggy carbonate rocks.

For better understanding of rock fragmentation mechanism and correlative influence factors under the cutter penetration, a set of two-dimensional wedge indentation tests was conducted. Nondestructive detection techniques, including infrared thermography and acoustic emission, were employed to capture rock damage evolution information. Combined with experimental observations, the cavity expansion model (CEM) theory was adopted to interpret the temperature rise differences for different rock damage zones, and the sizes of these zones were quantitatively determined based on the thermal distribution. It was thought that different thermomechanical coupling mechanisms in different damage zones cause their differences in temperature rise degrees. The quantitative estimation for damage zone sizes indicates the plastic zone and core zone initiate and develop sequentially rather than simultaneously. The main influence factors on rock indentation and damage evolution characteristics were also considered, including rock type, wedge indenter geometry and confining stress. Furthermore, some shortcomings of the classical CEM were discussed through the comparison of indentation pressure and damage zone size between the experimental value and theoretical estimation.

Through the acoustic emission (AE) test of gypsum, coal, concrete and sandstone specimens under uniaxial compression, the load axial deformation curves and AE parameters of four kinds of specimens with different lithology are obtained. The temporal and spatial evolution law of AE and the multifractal characteristics of the waveform before and after rupturing are analyzed. The results show that the uniaxial compressive strength of gypsum, coal, concrete and sandstone specimens increases in turn; the AE pulsing counts of the four specimens are consistent with stress changes, moreover, the maximum AE pulsing counts of gypsum, coal, concrete and sandstone specimens increase in turn; the spatial location of the four specimens is consistent with their macroscopic rupturing morphology, but the time of occurrence and the location of the distribution are different; the rupturing waveforms of the four specimens have multifractal characteristics, the multifractal spectrum Δf(α) of the four specimens when rupturing is smaller than that of Δf(α) before rupturing, and the Δf(α) before rupturing is smaller than that of Δf(α) after rupturing, the Δf(α) of gypsum, coal, concrete and sandstone specimens decreases at the corresponding stages. It is shown that the energy of the four specimens when rupturing is larger than that before rupturing, and the energy before rupturing is larger than that after rupturing, moreover, the energy of gypsum, coal specimen, concrete and sandstone specimens increases at the corresponding stages, this is consistent with acoustic emission pulse counts. The biggest rupturing moment gradually increased from gypsum, coal, concrete to sandstone. Through the analysis of temporal and spatial evolution law of AE and the multifractal characteristics of the waveform of four kinds of specimens with different lithology, to further understand the law of rupturing, and lay a theoretical foundation for the prevention and control of rock burst in coal mine.

To study the evolution of coal damage characteristics based on the infrared radiation temperature (IRT), we analysed the IRT characteristics of coal under uniaxial compression and established a coal damage model according to the relationship between the deformation and maximum IRT (MIRT). In addition, we further deduced a method for imaging the evolution of the surface stress field based on the IRT. The results reveal the following. (1) The MIRT–strain curve corresponds well with the stress–strain curve under loading, and the MIRT can effectively reflect the coal damage. (2) A coal damage evolution model can be established based on the accumulation of the IRT, which can effectively reflect the evolution and development of cracks and the ultimate failure of coal under uniaxial compression. (3) The calculated stresses based on the accumulation of the MIRT can effectively reflect the measured stresses during the destruction of coal. The peak value of the calculated stress–strain curve occurs before the peak of the measured stress–strain curve, providing an innovative approach for the monitoring and early warning of dynamic coal-related disasters. (4) The calculated coal stress field based on the IRT can effectively reflect the compressive deformation of coal, and the calculated stress field corresponds well with localized failure. These results provide a new non-contact measurement method for determining the surface stress field distribution of coal using IRT technology.

Amplitude variation with offset/angle of incidence (AVO/AVA) analysis is essential for hydrocarbon detection and reservoir characterization. Frequency-dependent AVO analysis plays an important role in seismic interpretation especially for the low-frequency seismic anomalies related to hydrocarbon reservoir. The diffusive-viscous model is used to explain these anomalies, but it does not consider the shear effects of rocks. In this work, we firstly extend the diffusive-viscous model to elastic case based on the mechanisms in a macroscopic porous medium. The elastic diffusive-viscous model describes attenuation of compressional and shear waves in a fluid-saturated medium and it reduces to the classic elastic wave equation in a special case. Then, we investigate the properties of reflection/transmission coefficients at an interface between two different elastic diffusive-viscous media. The reflection/transmission coefficients not only relate to the parameters of the media but also depend on the frequency. Two examples are given to analyze the dependence of the reflection/transmission coefficients on the frequency and incident angle at interfaces between gas-saturated sandstone and brine-saturated shale and between brine-saturated shale and oil-saturated sandstone. The results show that the magnitudes and phase angles of the reflection/transmission coefficients are significantly dependent on the frequency at lower frequency (<20 Hz). Finally, we apply the frequency-dependent reflection/transmission coefficients to the extended reflectivity method to model the propagation of the elastic diffusive-viscous wave in a layered medium. The modeling results show that the diffusive-viscous wave has strong amplitude attenuation and phase shift compared with those of elastic wave when the wave propagates across fluid-saturated layers.

Surrounding rock deformation control (SRDC) of roadways in deep three-soft coal seams (TCSs) is a significant technological difficulty that hinders the safety and high-efficiency mining of coal mines. According to the specific mining geological conditions of Liuquan Coal Mine, this study analyzed the deformation characteristics of surrounding rock under an original support scheme for the headgate (a typical asymmetrical roadway) in #3307 coalface. The analysis results showed that the surrounding rock displayed whole section deformation characteristics. The maximum value of roof subsidence was 369 mm, the maximum cumulative deformation value of the two sidewalls was 784 mm, and the maximum value of floor heave was 386 mm. On this basis, the mechanical structure models (roof, sidewall, and floor) of the roadway surrounding rock (RSR) were constructed, and the deformation mechanisms of the RSR in the TCS were revealed. Then, the principles for the SRDC of this asymmetrical roadway in deep TCS were proposed, the support parameters of the headgate were optimized, and the numerical simulation analysis of support effect was also performed using FLAC^2D software. Engineering application results indicated that the surrounding rock deformation of the headgate was better controlled. Under the optimized scheme, the maximum value of roof subsidence was 50 mm, the maximum cumulative deformation value of two sidewalls was 120 mm, and the maximum value of floor heave was 80 mm, which verified the feasibility of the optimized support parameters.

In towed-steamer marine seismic acquisition, crossline data are fairly sparse which makes crossline wavefield reconstruction very difficult. Therefore, reconstructing the sparse wavefield becomes a fundamental and crucial step in seismic processing flow. Recently, compressed sensing has provided new insights into the data recovery problem, which combines a sparsifying transform, a sampling strategy, and a sparsity promoting algorithm. Shearlet transform is provided with a fairly good sparse representation of seismic data, and is very robust in the application of seismic wavefield reconstruction. Using multi-component measurement techniques, we propose a multi-component crossline wavefield reconstruction method based on sparse shearlet constraint inversion. By combining the pressure wavefield and its crossline gradient obtained through V_y measurements, the proposed method can effectively reduce the multiplicity caused by a limited number of samples. Both synthetic and field data have demonstrated that the method proposed in this paper, compared with the traditional wavefield reconstruction method, achieves better reconstruction resolution in the case of extremely sparse samplings and effectively suppresses the aliasing effect.

At present, most studies have considered partial saturation and aligned fractures separately. However, these two phenomena exist simultaneously in most fractured reservoirs, such as carbonate reservoirs and tight sandstone reservoirs. In this paper, we develop a periodically layered model with alternating fractured layer saturated with gas and water-bearing porous layer to simultaneously model partial saturation and aligned fractures, which is an equivalent viscoelastic vertical transversely isotropic medium. We assume that the two types of attenuation are independent of each other. Firstly, we analyze the phase velocities and attenuation coefficients of quasi-P (P) and quasi-S (S) waves with frequency and incident angle, when the thickness fraction of fractured layer is 0.5. It shows that the attenuation coefficients of P-wave are much greater than the S-wave, when the incident angle is smaller than 30°. Then we analyze the frequency-dependent characteristics of the P-wave with different thickness of the fractured layer related to gas saturation. The attenuation of P-wave increases significantly with gas saturation in the frequency band from 10 to 100 Hz. Finally, we re-derived the frequency-dependent amplitude versus offset equation of anisotropic media to analyze the dispersion characteristics of the P-wave reflection coefficients. The reflection magnitude decreases with frequency and the reflection coefficients show significant anisotropy at high gas saturation. The dispersion and attenuation of P-wave largely depends on the gas saturation.

Seismic attributes are useful tools for identifying and characterizing geological properties. Seismic interpretation can be supported by seismic attribute analysis. Common seismic attributes use mathematical relationships, based on the geometry and the physical properties of the subsurface to reveal features of interest. Some key seismic attributes that can be used in the identification of channels are textural attributes, based on the Grey Level Co-occurrence Matrix (GLCM), a 2D matrix representing the amplitude values of the reference pixel versus the amplitudes of the neighboring pixels. Using the information gathered from the texture attributes, entities such as channels can be identified with ease and the Earth's structural information can be determined directly. In this paper, applications and practices of the textural attributes based on the GLCM method are shown in detecting and revealing channels in the structure of the Sarvak formation oil field in south-west Iran.

Conventional finite-difference (FD) methods for 3D acoustic wave modeling generally adopt 1D FD stencil along each coordinate axis to discretize spatial derivatives of the Laplace operator. It has been proved that when (2M)th-order spatial and second-order temporal 1D FD stencils are directly used to numerically solve the 3D acoustic wave equation, the modeling accuracy is second-order. The accuracy can be increased to (2M)th-order along 48 propagation directions by using spatial FD coefficients based on the time-space-domain dispersion relation. To improve the accuracy further, we design a novel temporal high-order FD stencil, which is a combination of the orthogonality and octahedron stencils, to discretize the 3D spatial Laplace operator. Based on the time-space-domain dispersion relation, we derive the corresponding FD coefficients using a plane wave theory and Taylor-series expansion. This new FD scheme can simultaneously achieve (2M)th-order spatial and (2N)th-order temporal modeling accuracies. Moreover, we further adopt a graphic processing unit to address the extensive computational cost in the 3D case. Dispersion and stability analyses indicate that our proposed FD scheme is more accurate and more stable than the conventional one under the same operator length M. The accuracy and efficiency advantages are also demonstrated by two 3D modeling examples.

One of the most significant challenges of constructing large underground spaces is to determine the allowable distance between these structures. For instance, a large distance between the caverns at a hydroelectric power plant incurs a higher cost due to the transfer of electricity from the powerhouse cavern to the transformer cavern via underground openings called bus tunnels and bus shafts. However, reducing the distance between the caverns would result in the undamaged rock pillar between the caverns being narrow. Thus, with regard to the interaction between the caverns and the induced stresses in the rock pillar, buckling may potentially occur. Based on the results of laboratory and in situ rock mechanics tests performed in the Bakhtiary dam and the HPP project, this paper includes reports on (but is not limited to): (A) laboratory tests such as 162 unconfined compression tests, 125 triaxial compression tests, 94 direct shear tests on rock discontinuities, 47 indirect tensile strength (Brazilian) tests; and (B) in situ tests such as 91 dilatometer tests, 12 large flat jack tests, 48 plate load tests, 58 borehole slotter tests and 62 hydraulic fracturing tests. The geomechanical parameters of the rock masses surrounding the caverns are estimated. Then, the allowable distance between the powerhouse and transformer caverns is determined using analytical relations of buckling in thin pillars and numerical simulations based on the distinct element method.

The localization of diffractors is a great challenge for seismic data with a low signal to noise ratio, and it is also difficult to preserve the polarity characteristics of edge diffracted waves in the separated diffractions. In this paper, we present a method to locate the diffraction points and extract the diffractions from reflected data by using the Hilbert transform, the modified apex-shifted Radon transform (ASRT) and double-branch Radon transform. The Hilbert transform is used to weaken the impact of dominant reflection amplitude on detecting weaker diffractions in instantaneous phase data. The modified ASRT and double-branch Radon transform are applied to locate the apex of diffractions and preserve the polarity reversal of edge diffracted waves emitted from reflector discontinuities, respectively. The synthetic and real data applications illustrate that the method not only accurately locate the diffraction apices but also discriminate the responses of the small-scale scattering objects and the reflector edges.

Downward continuation of potential field plays an important role in the interpretation of gravity and magnetic field data. For its inherent instability, the continuation operation is extremely sensitive to noise. In this paper, we present an improved stable downward continuation method based on the computation of stable vertical derivatives obtained by the Tikhonov regularization and the truncated Taylor series expansion of the field. By using the Tikhonov regularization operator in the frequency domain, the filtering is also performed simultaneously while computing the vertical derivatives, and then the stable derivatives and downward continuation are obtained. The calculation results of synthetic and real data show that the proposed method can achieve stable and accurate downward continuation for the magnetic data.

Missing traces complicate the seismic data processing and may cause difficulty in geological interpretation. We present a simple but efficient normalized Gaussian weighted filter (NGWF) method for seismic data interpolation that is suitable for reconstruction despite a large number of missing traces in the data, and has low computational complexity. The missing data are filled with locally retained pixel information via the Gaussian weight. Numerical tests show that the reconstructed result using the NGWF method is better than that using dictionary learning, total variation, partial differential equation, and economic orthogonal rank-one matrix pursuit. In addition, the proposed approach is also applied to pre-stack and post-stack seismic section, and the results indicate that the new approach is applicable to the recovery of seismic data with missing traces.

The fractal characteristics of acoustic emissions (AEs) are widely used for monitoring and warning of coal and rock dynamic disasters such as coal and gas outburst and rock bursts. However, most research has focused on fractal behavior during coal and rock failure under uniaxial and conventional triaxial compression. For this study, we conducted true-triaxial multi-stage loading tests on coal under different stress conditions. Based on the AE count rate data collected from these experiments, we calculated the fractal dimension of every loading step by the Grassberger and Procaccia algorithm using phase space reconstruction theory. The results show that the AE count rate represents the load during the failure well. In the initial loading stage, AEs are very active; in the initial portion of the load maintenance stage, AE counts decrease gradually until they almost cease later in that stage. AE count rates during failure for all loading steps exhibit fractal features and show a generally consistent pattern. The fractal dimension fluctuates in the early loading stages and then begins to decline, reaching a minimum when failure occurs. The critical fluctuation coefficient where the fractal dimension begins to enter the continuous decline stage is about 55.5%–66.5% of the stress level. The relationship between the change of fractal dimension and the 'quiet period' of AE before coal failure is discussed and the proposal that the combination of two monitoring methods can more effectively predict coal and rock dynamic disasters is put forward.

The adsorption, permeability properties, and damage evolution of internal cracks are often not considered in simulation tests for coal and gas outbursts. Therefore, in previous studies of similar materials, the materials used may not be similar in the properties mentioned above. To solve these issues, the adsorption, permeability, mechanical, and acoustic emission (AE) response characteristics of a soft coal solid–gas coupling similar material (SCSCSM) were studied in an orthogonal experiment where gas adsorption, permeability, uniaxial compression, and AE tests were performed. The analysis of the experimental data revealed that the SCSCSM has mechanical, gas adsorption and permeability properties similar to those of soft coal. The mass fraction of humic acid sodium solution (HASS) was the main parameter, affecting physical and mechanical properties. As the mass fraction of HASS increased, the adsorption volume and permeability varied logarithmically and exponentially, respectively. Meanwhile, the failure pattern transitioned from extrusion damage to wedge splitting and brittle shear failure. AE response from the beginning to the peak stress can be divided into a slow increase stage and a rapid increase stage. A damage parameter experienced an initial rise, then a rapid decline, then a quick rise, and finally a slow increase. Through segmentation fitting, expressions of damage evolution mechanisms for each section were obtained. Through the study of the SCSCSM's internal gas storage, transport, and mechanical properties, AE response characteristics, and multiscale evaluation of mechanical response, this study has laid a foundation for the subsequent development of solid–gas coupling similar simulation materials and physical simulation experiments of coal and gas outburst for soft coal seams.

Various researchers have shown that the decomposed wave-field can obtain a more accurate Green's function with seismic interferometry (SI). In the deviated and horizontal wells, traditional methods based on the difference of apparent velocity in the vertical well fail to separate downhole drill-bit source wave-field into up- and downgoing components because of the similar moveout. In recent years, one-way Green's function retrieval with the Marchenko method has been successfully applied to borehole data. Inspired by a data processing method that utilizes surface and borehole data to separate the wave-field, we have recently developed a wave-field decomposition scheme that only uses the surface recordings. The advantage of this method is that it does not need the knowledge of media properties, which is completely data-driven. Then we use the decomposed wave-field to retrieve the reflection response around the well with inter-source SI methods. The numerical experimental results show that the Marchenko method can accurately separate the wave-field. Simultaneously, the response retrieved by inter-source SI is close to the target area, and the influence of the irrelevant formation is removed.

Because of the large original stress in deep mining, compared with shallow mining, it is more likely to cause the occurrence of dynamic disasters such as rock burst, coal and gas outburst by the mining-induced stress concentration. Therefore, it is of great significance to master mining-induced stress distribution in deep mining. Mining-induced stress distribution of the working face in a kilometer-deep coal mine has been studied in this paper. The paper presents a study incorporating field monitoring, numerical simulation and theoretical analysis. Through analysis of field measured results, the following conclusions are made. For the area of the working face whose upward side and lateral direction are both unexcavated, the influence scope of advancing abutment pressure is 73 m; for another area whose upward side and lateral direction are both excavated, the influence scope is 64 m; for the area whose upward side is excavated and whose lateral direction is unexcavated, the influence scope is 31 m. Meanwhile, according to roadway displacement deformation monitoring, the influence scopes of advancing abutment pressure of the above areas are respectively 70 m, 68 m and 45 m, consistent with field stress monitoring results. In addition, the results obtained by FLAC^3D numerical simulation fits relatively well with field measured results. In the end, combining with theoretical analysis, it determines the high stress concentration zone of the working face, provides a decision-making basis for taking advanced pressure relief measures and offers a reference for the safe mining of both follow-up working faces and other working faces with similar conditions.

In order to study the influence of fracture evolution characteristics of rock-like materials under different strain rates, we use river sand as aggregate and cement, and gypsum and starch as binder to make a rock-like specimen, and uniaxial compression experiments are carried out with different loading rates by a DYD-10 electronic universal testing machine. The average strain rate of rock samples under different loading rates was obtained, and the characteristics of crack evolution of rock samples under different strain rates were studied. The results show that with the increasing strain rate, the peak strength of rock-like specimen increases; the main fracture gradually develops to the direction paralleled to the maximum principal stress, which leads the failure form of the specimen evolving from shear failure to tensile failure. During the loading process, the specimen will enter the plastic stage from the elastic stage, and a certain 'reaction time' which increases with the increase of strain rate is needed. The energy rate which is released inside the specimen increases with the strain rate from slow to fast, then from fast to slow, allowing the surface crack to extend in the same trend; that is with the increase of strain rate, the specimens exhibit obvious brittle failure, and the average evolutionary rate of specimen surface increases logarithmically following the strain rate. Therefore, the study on the crack evolution characteristics of rock-like materials under different strain rates can provide some theoretical bases for similar physical simulation experiments.

We use an extended elastic impedance (EEI) inversion for quantitative reservoir characterization. The EEI approach is applied to both on-shore and off-shore seismic data where target reservoirs are gas-bearing sands located in sand-shale sequences. The workflow we adopt can be divided into three phases. The starting point is a petrophysical analysis in which the relationships between petrophysical and elastic properties are analyzed. The second step of EEI analysis uses a cross-correlation procedure to determine the best chi (χ) projection angles for the petrophysical parameters of interest (i.e. porosity, water saturation and shaliness). In the final step, pre-stack seismic data are simultaneously inverted into P-wave velocity, acoustic, and gradient impedances, and the last two elastic volumes are finally projected to χ angles corresponding to the target petrophysical parameters. The estimated porosity, water saturation, and shaliness values reveal a proper match at blind well locations. This work shows that EEI is an effective tool for lithology and fluid prediction in clastic reservoirs. The output of this work can be beneficial for static reservoir model building and volumetric calculation and can be also used to determine new potential drilling locations.

The damage inside rock caused by its stress history has an important influence on the rock failure process. In underground gas storage engineering, the gas injection and extraction process damages the reservoir. The results of microseism monitoring show that many microseism events occurred during the injection and extraction of the gas, although the working pressure did not reach to the failure strength of the reservoir. Damage can also be done by cyclic injection hydraulic fracturing technology, where the working pressure reaches the maximum value of the previous loop; many microseism events can be monitored, and the final stimulated reservoir volume improved greatly. In this paper, we focus on the effect of stress history on rock failure, based on the stress curve response and the acoustic emission (AE) response obtained from a cyclic loading experiment on the tight sandstone bed. Combining the strain–stress curves with the AE Kaiser or Felicity effect, the rock damage characteristic and mechanism are researched. It is concluded that after equal value cyclic loading more local fractures can be formed during a core's final rupture. Also, the rupture path changes, the main rupture is suppressed and the number of fractures increases. Multistage cyclic loading can also change the rupture mode, but the number of local fractures is smaller than the number generated after an equal value cyclic loading action. The damage inside the rock caused by historical stress action can be divided into crack damage and plastic damage; crack damage can be obtained by AE monitoring, and plastic damage can be monitored by both AE and the stress–strain curve. The plastic damage which was stored in the stress history affects the tendency of the main fracture to be derived and increases the local rupture.

Rock fracture mechanics have been widely applied to earthquake mechanics, hot dry rock geothermal energy extraction, hydraulic fracturing, mechanical fragmentation, rock slope analysis, geophysics, and many other practical problems. It is important for geological disaster identification and prevention to clarify the crack propagation mechanism in rock failure process. To further investigate the evolution of crack propagation and internal damage in brittle rock, and based on the way that rock mainly occurs shear failure, we conducted direct shear tests on sandstone. Our tests combined macroscopic/mesoscopic observation and acoustic emissions monitoring. We found that crack propagation under compressive-shear stress occurs in stages, including the initiation and propagation of tension cracks, which are then connected by shear cracks. As normal stress increases, the length of a single tension crack becomes shorter, and the cracks themselves increase in number. We found that tension crack propagation is accompanied by fewer microcracks; in contrast, shear crack propagation is accompanied by considerable microcracks. This process may induce a drop off in mineral particles through slipping, and it may ultimately produce a rock bridge. The main damage occurs after shear cracks appear during shear failure, especially when the normal stress increases.

A novel fuzzy logic mathematical formulation to obtain accurate synthetic seismograms by means of correlations with noise is presented in this work. Recently, the use of seismic noise, surface waves and seismic ambient information for describing the structure of the Earth has captured the interest of seismologists, geophysicists and in general, the geoscientist community. By means of seismic noise correlations, it is achievable to retrieve some important characteristics of the propagation medium (e.g. the Green's function and wave velocities). However, the precise retrieval values of such characteristics greatly depend on the amount of seismic noise (number of random sources) and even on the difficulty in describing the subsoil that constitutes the propagation media. The impossibility of having exact values of these parameters prohibits the estimation of the error in the recovery of the Green's function by conventional methods, which makes it necessary to choose alternative computational methods, such as fuzzy logic. Firstly, the equations applicable to the seismic noise correlation and its relationship with the Green's function are established, validating with previously published results, and later applying the fuzzy logic to estimate the error in the recovery of the Green's function. In the last section, we propose the design, training and implementation of a fuzzy inference system. To this end, our method is inspired from the Sugeno model, but with modifications that allow the entry of membership functions (in contrast to discrete values) corresponding to the number of environmental sources and to the soil type in question, as merely qualitative values. Based on these, the error in the recovery of the Green's function is calculated.

The characteristics of deep burial, great thickness and severe heterogeneity in the glutenite reservoir bring in the difficulty in the design and treatment of hydraulic fracturing. It is especially hard to control and predict the hydraulic fracture morphology, which is due to the gravel. A 2D fracture propagation model with flow-stress-damage coupling in the glutenite reservoir is established with the damage mechanics method. Based on the rock mechanics parameters in a glutenite reservoir, the influence of single gravel and multi-gravels on the hydraulic fracture propagation is investigated by numerical simulation. The results show that the hydraulic fracture morphology in the glutenite reservoir is influenced by gravel rock mechanics properties, matrix lithology and physical properties, and different failure patterns, fracture length after leaving the gravel and propagation direction are caused by reservoir stress conditions, fracturing treatment parameters and gravel size and shape.

Carbonate fractured gas reservoir detection is very significant for the process of oil-gas exploration. It is difficult to characterize the reservoirs properly by traditional post-stack seismic attributes, because of the complexity of mineralogical composition and fluid type. Based on rock physics, it becomes possible to effectively solve this problem. In this paper, we combine seismic azimuthal anisotropy analysis and P-wave (primary wave) dispersion inversion based on the appropriate rock physics model in order to provide a method for carbonate fractured gas reservoir prediction. Firstly, referring to the geology and logging data of a carbonate fractured reservoir in the S area of Tarim basin in western China, we introduce the Voigt–Reuss–Hill theory into the Chapman model and set up an appropriate model which includes the influences of lithology and physical and fluid properties. Then, through seismic forward modeling and inversion based on this model, we find that attenuation azimuthal anisotropy is very sensitive to fracture density, and P-wave dispersion is closely linked to fluid type. By comprehensive analysis of these two attributes, we can characterize the reservoirs well. Finally, both attributes were applied to analysis of seismic field data for carbonate gas reservoir discrimination in the S area of the Tarim basin. The results show that zones with strong attenuation anisotropy and intense P-wave dispersion are likely to be favorable gas reservoirs. This is consistent with trial production data, hence demonstrating the great advantages of our method in carbonate gas exploration.

In order to study the critical slowing down characteristics of acoustic emission signals produced by the failure of the sandstone, the YAW4306 computer controlled electro-hydraulic servo press and the CTA-1 type acoustic emission data acquisition system were used to carry out the sandstone uniaxial compression experiment. The experiment results show that the acoustic emission signals produced by the destruction of sandstone have obvious stage characteristics and the cumulative acoustic emission count has good correspondences with the damage of sandstone. The increase of slope of the cumulative count curve of the acoustic emission indicates that the destruction of sandstone is coming. The autocorrelation coefficient and the variance of the critical slowing down characteristics are studied in different lag step lengths and window lengths. It can be found that different window lengths and lag step lengths have influences on the autocorrelation coefficient and the variance. When the window length is equal, the autocorrelation coefficient cures corresponding to different lag step lengths are messy and are consistent only in some parts, and the corresponding variance cures are basically coincident. Before the sample is destroyed, the small increases of the variance curve represent the occurrence of large cracks. The sudden and large-scale increase of the autocorrelation coefficient and the variance of the acoustic emission count can be used as the precursor signal of the destruction of the sandstone sample. Compared with the autocorrelation coefficient, the precursor signal of variance is more obvious. This is of great theoretical and guiding significance for enriching and improving the acoustic emission monitoring technology of rock mass.

The coal and rock masses located in a fractured zone are generally subject to shear and tensile stresses and respective damages, which increase their permeability and produce new channels of gas migration. This directly affects the gas extraction and the safe mining of the adjacent coal seams. This experimental study of the single persistent fractured coal samples (SPFCS) in the fractured zone of the Huainan coal mine, China, investigates the stress–permeability relationships of the SPFCS under cyclic loading and unloading. The permeability of the SPFCS was found to be much higher than that of elastic coal samples and exhibited a decreasing trend with the effective stress. The longer the compression time, the greater the permeability loss, but the impact of the compaction time on the permeability loss gradually decreases with the increase in the compaction time. The mechanism of permeability loss and changes during the cyclic loading–unloading are analyzed based on the experiment results. The results show that the fracture surface crushing, re-arrangement, and compressional deformation of pulverized coal in the loading process lead to a drastic drop in permeability. Besides this, the axial permeability sensitivity to the confining stress is found to be much higher than that to the axial stress.

In this article, we find that the transformational matrix between the natural logarithm of the acoustic impedance and the reflection coefficient is a Toeplitz matrix. As a result, we can convert the matrix multiplication into convolution operation according to properties of the Toeplitz matrix. In this way, we calculate the convolution of matrices through a dot product operation in the frequency domain based on the convolution theorem. Thus a fast multi-trace impedance inversion method by using two dimensional fast Fourier transform in the frequency domain is proposed, which can greatly improve the inversion speed. Considering the non-convex Lp (0 ≤ p < 1) quasi-norm is more suitable for sparse optimization than the L1 norm, anisotropic total variation regularization based on the Lp quasi-norm is used to improve the inversion result. Synthetic seismic data and field data inversion results show that the proposed method improves the inversion speed more than ten times compared with the multi-trace inversion method with total variation (TV) regularization in the time domain. At the same time, the proposed method has the advantages over the inversion methods with TV regularization in the time domain of less inversion error and better depiction of thin layers.

Changes in the velocity, amplitude and attenuation of ultrasonic waves are accompanied by physical changes during rock failure. A large number of triaxial compression tests were performed to study the progressive failure of shale rock according to these physical properties. The tested shale samples had different bedding planes and were subjected to different confining pressures. During the experiments, ultrasonic wave testing was used to monitor the progressive failure process and to evaluate different characteristic points. Variations were interpreted by analyzing the ultrasonic velocity and amplitude. Failure points cause velocity drops that are greater in the P than in the S waves. The percentage wave amplitude decrease at dilatancy point was determined and that of the P wave is double that of the S wave, which indicates that the P wave is more sensitive. The shale sample attenuation was analyzed, and the results show that samples with high density and high homogeneity tend to have a higher attenuation coefficient.

Overburden strata movement can create problems in longwall coal mines at shallow depths located in the West of China, due to surface subsidence affecting the surface structures and sensitive land features. Solid backfill mining (SBM) has been successfully used in several mines to solve many subsidence related problems, including coal extraction under buildings, water bodies and railways, and protecting the sensitive landscape. Due to the relatively shallow depth of coal seam, however, the solid backfilling materials must have high compactibility (i.e. be stiff). Based on the longwall working face 15 061 in the Dong Ping coal mine, the different size of the backfill gangue and the affects of porosity, stress and strain, strain energy density and strain were obtained in the laboratory. The deformation and energy absorb of the gangue with different particle size during compaction were analyzed. A multi-layer, composite and elastic foundation mechanical model of the key layers in the shallow coal seam was built. The compression modulus of the backfilling samples with different particle size was obtained with which the bending deflection, stress and strain energy density expression of the critical layer under different particle size range were derived. The result shows that when adopting SBM with longwall in the mine coal seam, the gangue backfilling body can effectively reduce the deformation of the key layer and absorb the energy accumulated in the key layer during the bending process. It was determined that when the gangue particle size is less than 31.5 mm (the porosity is less than 32.9%), the key layer will not break and the gangue filling body can effectively absorb 99% of the energy during the key layer bending. Whilst a smaller backfill (gangue) particle size reduces the porosity thus improving the strength, the cost of the backfill increases and this must too be considered when deciding on the material specifications. The roof deformation and fracturing in the key strata were monitored during mining in the Dong Ping coal mine site. The roof was found to be deflected but with no tensile cracking of the key immediate roof strata, showing the successful implementation of SBM.

Based on Biot's poroelasticity theory for low-frequency range and Deresiewicz's boundary conditions, we first derive propagator matrices of multi-layered isotropic poroelastic media for elastic waves defined by displacement functions. Then we give the reflection and transmission coefficients of a thin-bed where there is only a fast P-wave incident. The reflection and transmission coefficients are functions of incidence angle, thin-bed thickness, frequency, Biot's elastic parameters and rock properties. Numerical simulations and comparisons with the solid-phase models show that, for models of a water-saturated thin-bed embedded by two water-saturated porous solid half-spaces, the reflections of fast P-wave, slow P-wave and converted S-wave versus incidence angle are of great difference. Not only do the thin-bed thickness and porosity affect the reflection coefficients' amplitudes and phases of the porous thin-bed, but also the existence of fluid further complicates amplitude-versus-angle characteristics of multi-waves. By comparison, the reflection characteristics of converted S-wave are more pronounced than those of fast and slow P-waves for small incidence. Meanwhile, slow P-wave reflections are sensitive to thin-bed thickness and porosity, which shows that an increasing thickness and porosity would result in a higher amplitude and a lower phase.

The shear strength of a soil–rock mixture is an important parameter in geotechnical engineering design and the stability analysis of large-scale geotechnical engineering structures such as earth-rock dams and slopes. To solve the problem of the large disturbances that are encountered in laboratory and in situ direct shear testing of soil–rock mixtures, a new method referred to as borehole pressure-shear testing was developed for the measurement of the shear strength of a soil–rock mixture. The mechanical and mathematical models used for the proposed in situ borehole pressure-shear test were established based on the principles of borehole shearing technology. The shear strengths of similar materials were measured by borehole pressure-shear tests and direct shear tests, respectively, and the test results were used to calibrate the working parameters of the apparatus for the borehole pressure-shear test. The borehole pressure-shear test was then applied to the on-site measurement of the shear strengths of different soil–rock mixtures with differing rock block proportions. Using the results of the in situ direct shear tests as reference, a strong linear correlation was observed between the results of a borehole pressure-shear test and those of an in situ direct shear test. This correlation was used to develop a method for checking the results of the proposed borehole pressure-shear test. This paper also discusses the application scope of the proposed test.

History matching (HM) is an important task that is performed once a reliable reservoir model is constructed during numerical reservoir simulation studies. This HM process requires modification of uncertain reservoir parameters in order to match historical production data. As a result of these modifications, HM has been a long-standing industrial challenge in terms of computational cost and time consumption and furthermore, it requires much experience from the modeler. The tight gas production profiles of a damaged formation used in this study have been difficult to match due to the complex flow mechanism, computational expensiveness and minimal interaction between production wells. In addition, incorporating complex fracture networks due to stress sensitivity into the field's reservoir model for prediction is also a major challenge. Therefore, this paper proposes supervised machine learning predictive data analytics techniques of multivariate adaptive regression splines (MARS), stochastic gradient boosting (SGB) and a generalized regression neural network (GRNN) to history match the target field's well productivity profiles. The obtained results from the machine learning simulation techniques indicate that, unlike the full-physics numerical simulator HM approaches, the practical turnaround CPU time required for obtaining the target field's history match trained models were less than a minute. Comparatively, in terms of the developed predictive models' statistical performance measures using root mean squared error (RMSE) and coefficient of determination (R²), the testing of the MARS and SGB history match models exhibit superiority over the GRNN model. The trained MARS and SGB models being the best from the testing phase were validated with a surrounding production well profile for blind HM which gave impressive quality match results for the MARS and SGB models. The obtained validated results were then compared to the random forest (RF) ensemble method with MARS (RMSE = 0.0063, R² = 0.9998) and SGB (RMSE = 0.0478, R² = 0.9931) demonstrating the advantages of our proposed models as compared to the RF method (RMSE = 0.0502, R² = 0.9928). Also, the models developed in this study do not require re-training when updating with newly available datasets for HM. In all, the MARS, SGB and RF representative trained models will serve as robust alternative reservoir management and planning tools to supplement traditional numerical simulator HM in order to minimize substantial risks and uncertainties of the target field.

Ground subsidence is a very common phenomenon in mining areas, especially for those with a long mining period. After nearly half a century of mining activity, the concomitant disasters of Yingshouyingzi mining area gradually accumulated and have frequently occurred in recent years. In this work, the ground disaster situation and ground subsidence range appearing in the survey area were determined using field investigation and D-InSAR monitoring technology. Geophysical exploration technology (seismic prospecting and transient electromagnetic methods) and geological drilling exploration was adopted to ascertain the distribution of the underground goaf. The results show that the No. 4 and No. 6 coal seam goafs and second mining affected area were developed in the study area. Additionally, ten influencing factors were selected to evaluate the ground stability. According to the grading of each evaluation factor, the survey area was divided into four regions: unstable region, basic unstable region, basic stable region and stable region, based on a fuzzy comprehensive assessment method, which respectively occupy 15.57%, 60.28%, 15.17% and 8.98% of the total survey area. Through a comprehensive field investigation, the size and number of ground fissures and the housing damage rate decrease from the unstable region, basic unstable region, basic stable region to stable region, which indicates to us that the division result is consistent with the actual ground disaster situation. This, in turn, verified the rationality and validity of this evaluation method. Therefore, this study will provide help in forecasting and controlling the ground surface subsidence disasters caused by underground mining in the Yingshouyingzi mining area or other analogous areas.

The porosity calculation is the basis for the estimation of permeability and fluid saturation, which plays a significant role in hydrocarbon production. Acoustic logging is a critical method for porosity calculation but it suffers from partial distortions in horizontal wells. In addition, owing to high costs and imperfect technology, the horizontal logging data are always insufficient in the Northern Ordos basin, China. Therefore, porosity calculations based on partially distorted acoustic logs and insufficient horizontal logging data complicate the well logging interpretation. In this study, the abnormal acoustic log phenomena were analyzed based on the stratigraphic correlation and several influencing factors resulting in abnormal acoustic slowness in horizontal wells were summarized. Based on a detailed analysis, we proposed a novel porosity calculation model in which the normal acoustic log was combined with the compensated neutron log. Based on accurate porosity estimations, a fluid saturation model and a permeability model obtained from core analysis were developed and validated by three cases. A comparison with production data indicates that our models are effective and accurate for well logging interpretation, especially in horizontal wells. Therefore, the proposed models can be applied to the formation evaluation of highly deviated and horizontal wells for better hydrocarbon prediction in the future.

The seismic modulation model analyzes a seismogram from the low and high-frequency information, which is different from the traditional convolution model. In the modulation model, a seismogram is regarded as a modulated signal and its envelope is the amplitude-modulation component containing the low-frequency information. On this foundation, the envelope of seismograms can be used to recover a very smooth background structure. However, amplitude demodulation methods can only obtain the absolute value of the envelope, which cannot reflect the polarity changes of the amplitude information in seismograms. To solve this problem, we consider the low-frequency modulation from both the amplitude and polarity points of view. We extract a modulator signal with smoothed apparent polarity, which contains the amplitude and polarity information in seismograms. The new approach can broaden the modulation model theory for seismic signals. Good results from examples for application to envelope inversion demonstrate the good performance and potential of the proposed method.

Field experimental studies are mostly conducted from a technological approach, which helps to advance technological improvements in instrumentation and data processing schemes. In combination with a project initiated to explore the deep structures beneath South China led by the Institute of Geology and the Chinese Academy of Geological Sciences, the field experiment in this study was utilised to perform a contrast experiment between the self-developed GEI broadband seismic recorder and the universal Reftek 130 broadband seismic recorder. The power spectral densities (PSDs) and cross-correlation functions of ambient noise observed at ten self-developed broadband seismographs were calculated and analysed. The results obtained through the noise PSDs show the following: (i) strong diurnal variational characteristics of the high-frequency noise PSDs agree well with regular daily human activities, indicating that the high-frequency components of noise are generated by human activities; (ii) the low-frequency noise PSDs from all stations were approximately coincident, and they are believed to be the result of interactions between oceanic waves and continental coastlines; and (iii) strong amplitude asymmetries in the vertical cross-correlation results imply the predominance of noise sources toward the southwest of the deployment. This study may potentially strengthen the mutual promotion of the development of broadband seismographs, the reasonable deployment of broadband seismic stations and the methodology of examining corresponding broadband records.

Massive hydraulic fracturing (MHF) technology is widely used to increase the stimulation reservoir volumes in the development of shale hydrocarbon reservoirs by pumping large amounts of fracturing fluids and proppants at a high injection rate. However, fresh water dissipation and the flowback fluid pollution created by this technology brings serious environmental problems. Moreover, the post-production of MHF is uncertain and some fractured wells keep a low production level all the time. It is therefore necessary to find an economical treatment size to satisfy the actual geology position of shale reservoirs, such as mountainous and water shortage regions. The amount of proppant for MHF are a key parameter of treatment size, which also effect the volume of fracturing fluids and injection rate directly. A proppant quantifying model for MHF in a shale hydrocarbon reservoir was developed. In this model, the complex fracture network was characterized as the enhanced permeability area (EPA), and then a correlation was built between the amount of proppants and the EPA based on the Warren–Root model. When the EPA parameters were optimized by a reservoir simulator according to the post-production and net present value, the optimum volume of proppants for a specific shale well can be obtained easily. The new model has been applied at the first horizontal well in Jianghan shale oil field and three horizontal and eighteen vertical wells in Western Sichuan shale gas field successfully. Compared with the results of the early empirical design method used in Western Sichuan, this approach shows a better post-production.

The pore-scale location of hydrates exerts strong control on the macroscale physical properties of hydrate-bearing sediments. Many microfocus x-ray computed tomography (CT) devices have been used to detect the pore-scale spatial distribution of water, free natural gas, hydrate and sediment within the pore spaces of hydrate-bearing sediments. However, it is not easy to identify these four phases for intersection of grayscale intervals in CT images based on the usually obtained bimodal or trimodal histogram of grayscale in the threshold segmentation method, where four thresholds are required. To help deal with the overlapping areas of the grayscale in CT images, the Markov random field (MRF) is employed to promote the identification result of each phase, in the concept of maximum a posteriori (MAP) probability based on Bayes' theorem. After validation in the example of Berea sandstone (voids and solid), this method behaves well in hydrate-bearing sediment, which is consistent with the hydrate saturation of the experiment result, by finding the appropriate grayscale intervals and potential energy function.