查看更多>>摘要：Combining seismic data with a constrained model can obtain a high-resolution inversion result. However, it is very difficult to obtain an accurate low-frequency model because of the lack of wells in the offshore exploration area. We propose a multi-scale seismic envelope inversion method based on sparse representation to solve the problem of seismic inversion in offshore well-less areas. First, we demodulate the envelope of the seismic signal based on signal modulation theory and take it as the low-frequency component for inversion. Then, decompose the seismic signal based on MPSTFT (Short-Time Fourier Transform based on Matching Pursuit algorithm) method to provide high-resolution components of intermediate-frequency and high-frequency. Next, we take the linear impedance model as the initial model and update the inversion results by multi-scale inversion based on Bayesian inversion theory. Finally, we use the synthetic data to demonstrate the effectiveness of the proposed method and apply it to real seismic data. Comparing inversion results, the result of the proposed is more accurate and possesses a higher resolution. The results show that the proposed method has good adaptability to solve the problem of offshore well-less area inversion with a high-resolution inversion result.
查看更多>>摘要：Synthetic logs can help in the identification of petrophysical and geological properties of reservoirs, where the actual well logs are incomplete or absent. This study presents new and novel machine learning (ML) algorithms to generate pseudo well logs using the readily available conventional wireline logs. The machine learning algorithm works well with conventional wireline logs because they can deduce implicit relationships and efficiently detect trends in the logs. Moreover, identifying ups and downs (or peaks and valleys) of the subsurface characteristics is essential for any log. In this work, we have elucidated the application of Light Gradient Boosting Machine (LightGBM) and compared its performance with Category Boosting (CatBoost) and Random Forest (RForest). Grid search cross-validation (GridSearchCV) was done to optimize the hyperparameters of the algorithms towards a better balancing between accuracy and speed. To check the robustness of the algorithms, a number of input and output logs, considering variation in trends of logs with depth, were chosen to train the network. The well logs from Assam-Arakan Basin (India) include neutron porosity (NPHI) log, photoelectric (PE) log, caliper (CALI) log, density correction (DRHO) log, gamma-ray (GR) log, and bulk density (RHOB) log along with depth. We have evaluated the well log models and machine learning algorithms using determination coefficient (R2), mean square error (MSE), and root mean square error (RMSE) for training, testing, and validation. It has been shown that the use of machine-learning algorithms to generate synthetic logs improves reservoir characterization since they are computationally efficient, accurate, and cost-effective. The results showed that the LightGBM outperformed all the other algorithms in terms of speed and accuracy, in addition to its simplified hyperparameter tuning.
查看更多>>摘要：The wave equation acts a pivotal part in seismic data processing. We derived two time-domain pure qP viscoacoustic wave equations suitable for attenuation anisotropic media, providing a choice for pure qP-wave forward modeling and inversion in attenuation anisotropic media. Our new qP-wave equation in vertical transversely isotropic (VTI) media are based on the dispersion relation for qP-wave in VTI media and obtained by the relaxation functions of the standard linear solid model and the Kjartansson's constant Q model respectively. Anelasticity including amplitude attenuation and phase dispersion can be dealt with by the proposed wave equation separately. With the coordinate transform, the corresponding two pure qP-wave viscoacoustic anisotropic wave equations for titled transversely isotropic media also are derived. Different from the common viscoacoustic anisotropic wave equation (a coupled second-order partial differential equations system), the new wave equations are simplified by decomposing the original pseudo-differential operator into a differential and a scalar opera- tors. For numerical calculation, the new wave equations can be solved more efficiently than the coupled wave equations. Meanwhile the new wave equations could simulate pure qP-wave steadily in attenuation anisotropic media without quasi-SV wave artifacts. Some synthetic examples, including attenuation Hess and Marmousi-2 models, demonstrate the feasibility of the derived pure qP-wave viscoacoustic wave equations in transversely isotropic media.
查看更多>>摘要：To automate time-consuming and experience-based analysis of elastic wave velocities in rock samples, we propose a method of determining the arrival time of experimental waveform data using machine learning. Our model is one-dimensional semantic segmentation based on U-net utilizing ResNet and attention mechanisms. The results demonstrate high accuracy of travel time estimation (0.0125 mu s) of two types of waves (P- and S-waves). Our approach can estimate the travel time in any experimental device. This method reduces the interpretation time and human biases in analyzing laboratory data of elastic waves. Therefore, this approach contributes to the efficient evaluation of subsurface structure from seismic properties.
查看更多>>摘要：Nature fractures developed in tight gas-bearing sand reservoirs significantly increase reservoir porosity and permeability and vary in scale, angle, aperture, density. The detection of effective hydrocarbon fractures are requirements for commercial production from these reservoirs. Based on the equivalent medium theory, we propose an approach to eliminate the influence of low-productivity horizontal bedding fractures and directly extract the orientation and intensity information of effective high-angle fractures in the reservoir where hori-zontal bedding fractures are mainly developed. First, we assume that the complex tight gas-bearing sand reservoir is considered as a weakly orthorhombic medium with a single suite of parallel vertical fractures embedded in a vertical transverse isotropy (VTI) medium. Then, we derive a linearized relationship between the reflection coefficient and the fracture orientation and intensity in an orthorhombic medium. Furthermore, we implement a Bayesian elastic impedance (EI) inversion workflow, in which the seismic data are transformed to EI datasets, and subsequently EI datasets are used to estimate the fracture orientation and intensity. Finally, the proposed approach is demonstrated by tests on synthetic examples and field data sets. The predicted results illustrate the approach is feasible and robust, and agree well with the log data and geological interpretation. Compared with the conventional method, our approach has the greater advantages to accurately predict the fracture characteristics. We conclude that the proposed approach can reliably produce the distributions and properties of vertical fracture systems, which may provide crucial fracture information for tight gas-bearing sand reservoirs characterization.
查看更多>>摘要：Amplitude Versus Offset (AVO) methods relate seismic amplitude variations to subsurface pore fluid and lithology changes. Over the past decades, numerous AVO attributes have been extracted from seismic data and combined to detect seismic expressions associated with hydrocarbon-charged sediments. In this paper, we use an AVO attribute combination composed of gradient and scaled-Poisson reflectivity (SPR) to detect hydrocarbon expressions. Irrespective of sand-shale impedance contrast, the SPR and the gradient G produce negative anomalies for shale over gas saturated reservoir. We demonstrate that SPR-G product is a good alternative to the Intercept-Gradient product which works only for unconsolidated sands. The dataset used in this study is from Poseidon field, North Western Australia. The gas reservoirs belong to the Middle Jurassic-aged Plover Formation. The Plover Formation comprises sandstone, mudstone, and coal that deposited in a fluvial-deltaic environment. AVO analysis at a well location indicates the reservoirs belong to AVO Class II, which is characterized by small zero offset reflectivity and an anomalously large G. Due to the low impedance contrast between the reservoirs and the shale intervals, the I x G product failed to detect the fluid expressions of the reservoirs. The SPR x G product and SPR-G crossplot showed better fluid detection and lithology discrimination. Furthermore, the computation of the product SPR x G volume helped highlight the fluid response and spatial distribution of the reservoir units. New prospective undrilled areas could be identified using the SPR-G product.
Idi, Bello YusufMaiha, Abubakar IsaAbdullahi, Mukaila
11页
查看更多>>摘要：The upper Benue trough, northeastern Nigeria is characterized by prominent geologic and tectonic features of diverse scientific and economic interest. Lamurde hot spring is located within one of several deformational structures of the trough; the Lamurde anticline. In this work, we assessed the geothermal energy potential of the area using the Thermal Infra-Red (TIR) band of Landsat-8 data. We used four datasets representing the four seasons of the year to retrieve the Land Surface Temperature (LST) by converting the pixel digital numbers into LST based on the single-channel algorithm. We also used the retrieved LST to spatially map Radiative Heat Flux (RHF) based on the Stefan-Boltzmann radiation law. We validated the results by comparing the Landsat TIR-retrieved LST with MODIS LST product of the same area using a cross-validation technique. The results indicate a reliable fitting coefficient (R-2 = 0.801) and Root Mean Square Error RMSE value of 0.756 K. Although significant seasonal variation of both LST and RHF was observed, the rock outcrops associated with the hot spring high surface temperature and heat loss anomalies for all seasons of the year. Peak LST values of 43.7 degrees C, 35.6 degrees C, 29.4 degrees C, and 27.5 degrees C were respectively recorded in January, April, July, and October from the active thermal area. The average values of RHF obtained from the active thermal area are 11.78, Wm(-2), 10.76 Wm(-2), 1.22 Wm(-2) and 0.168 Wm(-2) for January, April, July and October respectively. These are much higher than the global continental value. Comparison with known active geothermal areas from different parts of the world indicates that the area has significantly high surface geothermal parameter indicators.
查看更多>>摘要：Reflection amplitude from rebar is the most commonly used parameter for condition assessment of concrete structures using Ground-Penetrating Radar (GPR). However, it was reported that such amplitudes might affect by several factors, including the chloride content, rust accumulated on the surface of steel bars due to corrosion, and the environmental conditions at the time of GPR data collection. The objectives of this study were to observe the change of GPR signals over time and to evaluate the effects of those factors on the reflection amplitude of steel bars. A series of six reinforced concrete slabs were fabricated with identical configurations but for different chloride contents. Two testing phases with the multiple GPR measurements were conducted both outside and inside an environmental chamber. In the first testing phase, the development of GPR signals was daily obtained from day one to day 90 in the laboratory conditions. In the second testing phase, the GPR data were collected inside the environmental chamber at an interval of 24 h. Relative Humidity (RH) was set at three levels of 55%, 70%, and 85%, respectively, while the temperature was varied between 5 degrees C and 40 degrees C. The test results from the first testing phase showed that the GPR signals developed at an exponential rate during the first three months. In addition, results from the second testing phase revealed that both the added chloride and the rust on the surface of steel reinforcement reduced the amplitude of rebar reflection. Regarding the effects of temperature, for sound (i.e., non-contaminated) concrete, the reflection amplitude decreased approximately 0.05 dB for every 1 degrees C increments. For the contaminated concrete, such ratio was found to increase proportionally to the chloride levels. Finally, the RH was observed to have insignificant effects on the amplitude of rebar reflection.
查看更多>>摘要：The coal water-filled zones have become a growing safety hazard, so effective detection techniques and accurate interpretation methods are of great concern. In this paper, we adopt multi-radiation source transient electromagnetic method (TEM) in the data collection, and employ joint imaging method in the data interpretation. A single-radiation source can only be coupled with the geological body from one side, making holographic photography problematic, but multi-radiation source can suppress random noise, improve the signal-to-noise ratio, and reduce the volume effect. Typically, the apparent resistivity method can reflect the electrical distribution characteristics, while the pseudo-seismic imaging method (PSI) can quickly locate the position and shape of the geological structure, so the two imaging methods can be combined. Therefore, firstly using multi-window time-sweep wavefield inverse transformation technology converts the TEM data into the multi-resolution pseudo-wave, then utilizing the joint interpretation method obtains the underground electrical distribution characteristics, the location of the water-filled zones and stratum's continuous undulations. In this paper, through the calculation of the theoretical model, the results verify the effectiveness of the proposed method. Through processing the field data in Gansu, China, the results demonstrate that the joint interpretation method can map the coal water-filled zones and reflect the geological structures.
查看更多>>摘要：The classical magnetotelluric (MT) sounding can be defined as data that are invariant under rotation of coordinates -a feature we call centrality- and are affected solely by electromagnetic induction effects -a feature we call all-induction. The classical sounding can be realized only in the case of laterally isotropic media and perfectly horizontal layering. However, in general it is possible to process data from several sites to make an approximation. For instance, the electromagnetic array profiling (EMAP) method addresses the issue of all-induction by means of spatial filtering. The method is very effective but its application is not practical for long profiles because it requires too many contiguous dipoles. A more practical version exists that does not require contiguous dipoles but neither of them addresses the centrality issue; in the first case because the data are taken along a single direction, and in the other because it uses traditional orthogonal modes. In this work we improve over the last approach by introducing centrality to make the approximation closer to the classical sounding. We use the determinant of the impedance tensor, which is the only invariant among all that are known that can handle centrality, the galvanic distortions and also the isolation of all-induction effects through two-dimensional inversion. This approach to the classical MT sounding is illustrated using the synthetic dataset COPROD2S2 and the field dataset BC87 from British Columbia, Canada, which are commonly used for testing new ideas. We also apply it to a recent profile over the Colima Graben, Mexico.
NSTL
Elsevier