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One of the most urgent problems of oil and gas reservoir monitoring is the assessment of fractured reservoir infill type — with fluid-filled, gas-filled, or closed (no-reservoir situation) fractures, which is of significant value for time-lapse seismic technology. We used the grid-characteristic method for numerical modeling of seismic responses from fractured periodic elastoacoustic structures. We consider every single fracture individually (without using the effective medium approach), and we set explicit boundary conditions on fracture surfaces. We assume realistic height-to-thickness ratios — fracture opening (aperture) — equaling three to five orders of magnitude. These techniques make our models as close to real fractured reservoirs as possible. Analyzing the simulated seismic responses, we solve the problem of assessing the fractured reservoir infill type. As a result, previously unknown properties of seismic responses from fractured reservoirs were revealed. We use amplitude variation with offset (AVO) as the main tool for the analysis of the fracture infill type effect on the seismic response in three frequency ranges. Three out of four models exhibit a stable positive AVO gradient regardless of the rock type and frequency range. The analysis of linearized Zoeppritz equations confirms such AVO behavior. We have developed quantitative criteria (indicators) for recognition of a fracture infill type. Amplitude-frequency analysis is shown to expand the capabilities of the infill type recognition. Thus, a method for determining the fractured reservoir infill type is established for carbonate and shale formations, which could become the basis for a new direction in time-lapse technology.

The article is devoted to the study of the propagation of elastic waves in a fractured seismic medium by methods of mathematical modeling. The results obtained during it are compared with the results of physical modeling on similar models. For mathematical modeling, the grid-characteristic method with hybrid schemes of 1-3 orders with approximation on structural rectangular grids is used. The ability to specify inhomogeneities (fractures) of various complex shapes and spatial orientations has been implemented. The description of the developed mathematical models of fractures, which can be used for the numerical solution of exploration seismology problems, is given. The developed models are based on the concept of an infinitely thin fracture, the size of the opening of which does not affect the wave processes in the fracture area. In this model, fractures are represented by boundaries and contact boundaries with different conditions on their surfaces. This approach significantly reduces the need for computational resources by eliminating the need to define a mesh inside the fracture. On the other hand, it allows you to specify in detail the shape of fractures in the integration domain, therefore, using the considered approach, one can observe qualitatively new effects, such as the formation of diffracted waves and a multiphase wavefront due to multiple reflections between the surfaces, which are inaccessible for observation when using effective fracture models actively used in computational seismic. The obtained results of mathematical modeling were verified by physical modeling methods, and a good agreement was obtained.

Schoenberg’s mathematical model of fractured geological media has been widely used in studies related to seismic exploration of oil fields. This paper proposes to use this model for computing wave processes in geological media by the grid-characteristic method. In that case, the sought-for functions are components of the velocity vector and stress tensor in the vicinity of the fracture, the values of which are determined at grid points. We simulated seismic pulse propagation through a homogeneous elastic medium with a fracture in the case that the wave front is totally reflected from the fracture edge. We used the grid-characteristic method in simulating wave fields with Schoenberg’s and two-edge fracture models. It is found that the models produce broadly similar results.

Shallow gas in ground water geological layers is of great danger for drilling rigs in the case of accidental opening of gas deposits. The gas may rise towards the water surface, and its emission into the atmosphere may threaten the environment. It is very important to forecast the gas emissions in order to prevent catastrophic destruction of drilling rigs and loss of human lives. This paper presents the results of numerical simulations of seismic wave propagation towards the water surface in models with gas deposits in a layered soil for the 3D case. The modeling is carried out for a 4-year period for layers located at a depth of 1000 m from the sea bottom. The calculation results (wave patterns and seismograms) show that the gas may approach the water surface in the 4th year of the calculations. The results for a 3D problem are in agreement with those for a 2D problem obtained by the authors earlier. This is very important, since the calculations can be greatly simplified.

Heterogeneous media with fractured geological structures are widely spread, and therefore, they need a very careful exploration. In this work, we present the results of modeling the seismic waves spread through the homogeneous and heterogeneous media with single fractures and fracture clusters using the grid-characteristic method. We analyze the seismic reflections from inclined fractured structures described by the model of a two shore extremely thin fracture. The models with little differing and significantly differing characteristics for single fluid- and gas-filled fractures and fracture clusters are analyzed. The results demonstrate the dependence of the normal components of the velocity distribution from the media parameters.

The problem of detecting the hydrocarbon deposits in the heterogeneous media is very important and difficult for solving. We suppose the grid-characteristic method of the third order of accuracy for solving the problem of the direct modeling of the seismic waves spread in such a medium with the presence of gas cavities and without them. The numerical method used in all the computations is described in detail. We present the results of modeling, the wave fields of the normal component of the seismic velocity, and the seismograms for the models of the heterogeneous media with several gas cavities and without them. The results demonstrate the possibility of detecting the seismic reflections from the geological layers and gas cavities. In the previous work, we solved a problem of modeling the seismic waves spread through the heterogeneous media with the use of the transparent method, which also showed the correct results. In this work, we carry out the comparative analysis of the previous results with the new ones. The grid-characteristic method of the third order of accuracy and the transparent method are both appropriate for solving the described problem in general. However, the results, which were obtained using the grid-characteristic method of the third order of accuracy under consideration the contact conditions between the geological layers, demonstrate the clearer seismic reflections and the more accurate velocity meanings near the contact boundaries between different media respect to the transparent method, which does not consider any contact conditions between the geological layers.

Ice constructions, such as icebergs and ice fields, are of great importance for studying as they influence strongly the seismic exploration of the Arctic region. The researchers often ought to use the bad conducting materials for decreasing the wave reflections from the ice constructions. The effectiveness of such inclusions has not been proved yet. This paper presents the results of computer modeling for the elastic waves spread in the geological media of the Arctic region. We analyze the influence of the plastic inclusion on the wave field and on the seismograms. The difference between the x-components and y-components of the velocities in models with the plastic inclusion turns to be insignificant in comparison with the models without any plastic inclusion.

Today, the exploration of the Arctic region is one of the most important direction of research in our country, because large amounts of unexplored oil and gas deposits are located there. Large hydrocarbon deposits are situated within the Northern seas. Their development is complicated by gas explosions resulting from an accidental opening and further spread of the gas. Since the region with gas layers cannot be frequently monitored, an area with already detected gas deposits is numerically modeled instead. In this work, seismic waves propagating in multilayered geological models with gas-containing inclusions were numerically modeled over a four-year interval by applying the grid-characteristic method. Wave patterns of seismic reflections and seismograms for the described problem were obtained. The wave patterns and seismograms obtained in the two- and three-dimensional cases were compared. The results were found to be in good agreement.

This paper presents a novel approach to modeling the propagation of seismic waves in a medium containing subvertical fractured inhomogeneities, typical for mineralization zones. The developed method allows us to perform calculations on a structural computational grid, which avoids the construction of unstructured grids. For the calculations, the grid-characteristic method is used. We also present a comparison of the proposed method with the one described at earlier works and discuss the areas of its practical application. As an example, the numerical results for a cluster of subvertical fractures are given. A new approach for modeling fractures makes it quite easy to incorporate fractured objects into the seismic models and perform calculations without using algorithms on unstructured and curved grids.

Today the Arctic is one of the most important regions, where lots of oil and gas deposits are located. The Arctic contains different ice formations that give rise to problems of the North seas’ exploring. The models ought to simulate the situations with the presence of ice constructions and oil slices. The main goal is to find the difference between responses from oil slices and ice formations. This paper represents the modeling results with ice cover and ice field. Wave patterns and seismograms are depicted for each model. Different cases of installing the source of impulse and receivers are examined.

We present the solution to the problem of detecting the gas layers in the Arctic conditions through the numerical modelling of the seismic waves spread in the heterogeneous media. The grid-characteristic method of the third order of accuracy is used in all the computations. We build the models with the different numbers of the gas layers and analyze the full wave fields in the heterogeneous media and the anomalous fields, excluding the seismic reflections from all the geological layers except for the gas layers. The results demonstrate the possibility of applying the grid-characteristic method to solving these problems. The result seismograms allow us to determine the location of the gas layers through collecting the time moments of the coming reflections from the gas layers to the seismic receivers.

The Arctic region contains lots of underground gas layers closed from the outside. In case of their opening, the gas is of great danger for the surface buildings and drilling equipment. In this work, we observe the main dangerous gas reservoirs – gas cavities and methane bombs. We build the mathematical models of these heterogeneities and presented the main mathematical equations allowing calculating the seismic waves spread through them correctly. The grid-characteristic method of the third order of accuracy is used in all the computations. We demonstrate the results of modelling the seismic waves spread through the heterogeneous medium with the gas cavities and through the homogeneous medium with the methane bomb. The analysis of the differences between the models is carried out. The problems of computing the models with gas cavities and with methane bombs need different approaches for the correct calculations, though the problem formulations are similar.

Gas emissions occur quite often in the North seas while carrying out oil-extracting works in the area. It is very important to be able to forecast such gas accumulations spread for further taking appropriate measures to avoid such emissions. This chapter represents the results of modeling of the spread of seismic waves in the layered structure of soil with present gas pockets for the 2D formulation of the problem. The seismograms and wave pictures have been obtained. The approach of gas layers towards the surface of the integration area on the 4th year of computation is shown.

The paper presents the results of application of a grid-characteristic method to simulation of wave processes in media with linearly-elastic and acoustic layers on the example of seismic exploration of the Arctic shelf. The grid-characteristic method correctly describes the contact and boundary conditions. The results of numerical simulation are presented, the method is shown to be applicable to solution of seismic exploration problem on the Arctic shelf.