Journal of Geophysics and Engineering - Latest Papers

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Latest articles for Journal of Geophysics and Engineering
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Pore-scale identification of multi-phase spatial distribution of hydrate bearing sediment

Thu, 07/12/2018 - 7:00pm
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 ...

Modeling of quantifying proppants for stimulation reservoir volume fracturing in a shale hydrocarbon reservoir

Thu, 07/12/2018 - 7:00pm
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...

Seismic modulation model and envelope inversion with smoothed apparent polarity

Mon, 07/09/2018 - 7:00pm
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 ...

Development of machine learning predictive models for history matching tight gas carbonate reservoir production profiles

Mon, 07/09/2018 - 7:00pm
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), ...

A field experiment with self-developed broadband recorders and a preliminary characteristic analysis of the data records

Mon, 07/09/2018 - 7:00pm
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...

Soil–rock mixture shear strength measurement based on in situ borehole pressure-shear tests

Mon, 07/09/2018 - 7:00pm
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...

Ground stability evaluation of a coal-mining area: a case study of Yingshouyingzi mining area, China

Mon, 07/09/2018 - 7:00pm
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 un...

Improved horizontal well logging porosity calculation for a gas reservoir in the Northern Ordos Basin, China

Mon, 07/09/2018 - 7:00pm
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...

Fast multi-trace impedance inversion using anisotropic total p-variation regularization in the frequency domain

Thu, 06/28/2018 - 7:00pm
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 co...

Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China

Thu, 06/28/2018 - 7:00pm
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 th...

Reflection and transmission coefficients of poroelastic thin-beds

Thu, 06/28/2018 - 7:00pm
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-vers...

Study of ultrasonic wave characteristics of shale in triaxial compression tests

Thu, 06/28/2018 - 7:00pm
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 t...

Relation between crack propagation and internal damage in sandstone during shear failure

Mon, 06/25/2018 - 7:00pm
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...

A fuzzy inference system applied to estimate the error in the recovery of the Green’s function by means of seismic noise correlations

Mon, 06/25/2018 - 7:00pm
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 comp...

Numerical investigation of hydraulic fracture propagation in the glutenite reservoir

Mon, 06/25/2018 - 7:00pm
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 ...

The precursory information of acoustic emission during sandstone loading based on critical slowing down theory

Mon, 06/25/2018 - 7:00pm
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...

Carbonate fractured gas reservoir prediction based on P-wave azimuthal anisotropy and dispersion

Mon, 06/25/2018 - 7:00pm
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 attenuatio...

Experimental study of stress–permeability behavior of single persistent fractured coal samples in the fractured zone

Mon, 06/25/2018 - 7:00pm
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 experimen...

The complexity of the fracture network in failure rock under cyclic loading and its characteristics in acoustic emission monitoring

Wed, 06/20/2018 - 7:00pm
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 charact...

Estimating petrophysical reservoir properties through extended elastic impedance inversion: applications to off-shore and on-shore reflection seismic data

Wed, 06/20/2018 - 7:00pm
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 prope...

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