Real Geological Media Research Articles

Прямая и обратная динамическая задача пороупругости

In applied problems related to propagation of elastic waves, it is often necessary to take into account porosity, fluid saturation of the media, and the hydrodynamic background. Real geological media are multiphase, electrically conductive, fractured, porous, etc. When propagating, seismic waves dissipate due to the absorption of energy. In this paper, the wave propagation process occurs in terms of partial densities of phases, stress tensor, pore pressure, and velocities of the corresponding phases. In the first section, for completeness, the presentation presents a quasilinear system of equations of the poroelasticity theory [1-3]. In the second section, the corresponding linear system of equations of the poroelasticity theory for a homogeneous medium is obtained. In the third section, we construct a fundamental solution for the system of equations of the poroelasticity theory obtained in the second section. In the final section, the inverse poroelasticity problem of determining the distributed source in a half-space using additional information about the free surface mode is considered.

The 3D Modeling of GATEM in Fractured Random Media Based on FDTD

Grounded-source airborne time-domain electromagnetic (GATEM) method is an effective detection method of geological survey. The real geological media are rough, self-similar characteristics, and the diffusion process is anomalous diffusion. This paper primarily considers the GATEM responses of a grounded wire source in random media. Von Kármán function is used to establish three-dimensional (3D) random media model and the GATEM responses are realized based on 3D finite-difference time-domain (FDTD) method. The method is verified by homogeneous half-space model. The electromagnetic responses of random abnormal body model are analyzed, and the results show that the abnormal body can be clearly identified. The electromagnetic responses of a fractured model are analyzed, and the results show that the tilt angle of the fault can be reflected.

Self-consistent problems of geophysics: A review

In the first part of the paper, the general information about self-consistent problems of geophysics is presented. It is shown that these problems most adequately describe the processes in the real geological medium. Examples of such problems are given. This section of the paper provides a number of new results which have not been published previously. These results are shown in italics in the text. The two subsequent sections address the analysis of the most elaborated self-consistent problems of geophysics: induced polarization and seismoelectrics.

Efficient modeling of seismic signature of patchy saturation for time lapse monitoring of carbon sequestrated deep saline reservoirs

Various mechanisms controlling the multiphase flow in a real geological porous medium such as those associated with carbon dioxide (CO2) storage in a saline reservoir can lead to a patchy saturation distribution. Successful monitoring of CO2 plumes using time-lapse seismic data under these conditions is a challenge due to the degree of uncertainty in the relationship between CO2 saturation and elastic (seismic) responses. Moreover, efficient modeling of these responses is vital for practical bookkeeping of stored volumes. We investigate the potential of using seismic methods to monitor CO2 in the subsurface by using reservoir simulation data generated in two types of models. The first one consists of a random distribution of absolute permeability, not unlike typical representation of geostatistical models of permeability. A second model, more geologically meaningful, represents an eolian sand deposit containing bounding surfaces. By combining reservoir flow modeling with seismic modeling, we demonstrate that the patchy nature of the saturation distribution, resulting from small-scale multiphase flow features commonly neglected in reservoir simulation exercises, can be seismically modeled with an equivalent stack of homogeneous isotropic/anisotropic layers and the elastic properties of this equivalent stack of layers can potentially predict the actual CO2 saturation within the reservoir to reasonable accuracy. We conclude that using efficient waveform inversions to extract homogeneous equivalent layer properties from time lapse seismic data and relating them back to the CO2 saturations is the key to the development of an effective monitoring strategy for carbon sequestrated reservoirs. We also believe that such an effective monitoring will require integrating reservoir flow simulation with seismic simulation for the given reservoir so that appropriate and feasible seismic modeling assumptions (like including anisotropy) can be determined prior to monitoring.

Depth imaging with amplitude correction for localized absorption anomalies. A case study from the North-West Australian shelf

Seismic amplitudes within target intervals are often affected by localized absorption anomalies in the overburden. In the North-West Australian shelf and in many other regions, the majority of such anomalies are caused by gas trapped in shallow sediments. We apply amplitude tomography to build a high resolution 3D absorption model and to take this effect into account in geological settings typical for the North-West Australian shelf. Two approaches have been developed recently to correct for absorption in depth imaging ? the first uses frequency independent models and the second based on Q- compensation with the linear frequency dependent assumption. We show how both techniques correct seismic amplitudes but their results are not frequency balanced. In order to achieve a better fit with the real seismic data, we propose and apply a mixed absorption model that combines frequency independent amplitude correction with the linear Q-compensation and reflects the presence of different effects responsible for seismic energy attenuation in real geological media. Prestack depth migration with this model corrects for the overburden effects and produces seismic data with spatially balanced amplitude and spectral characteristics.

Application of Multiple Point Geostatistics to Non-stationary Images

Simulation of flow and solute transport through aquifers or oil reservoirs requires a precise representation of subsurface heterogeneity that can be achieved by stochastic simulation approaches. Traditional geostatistical methods based on variograms, such as truncated Gaussian simulation or sequential indicator simulation, may fail to generate the complex, curvilinear, continuous and interconnected facies distributions that are often encountered in real geological media, due to their reliance on two-point statistics. Multiple Point Geostatistics (MPG) overcomes this constraint by using more complex point configurations whose statistics are retrieved from training images. Obtaining representative statistics requires stationary training images, but geological understanding often suggests a priori facies variability patterns. This research aims at extending MPG to non-stationary facies distributions. The proposed method subdivides the training images into different areas. The statistics for each area are stored in separate frequency search trees. Several training images are used to ensure that the obtained statistics are representative. The facies probability distribution for each cell during simulation is calculated by weighting the probabilities from the frequency trees. The method is tested on two different object-based training image sets. Results show that non-stationary training images can be used to generate suitable non-stationary facies distributions.

Experimental investigations of nonlinear seismic effects

Special experimental investigation using seismic vibrators allowed the propagation of periodic seismic signals accompanied by strong nonlinear effects to be demonstrated. These effects are caused by the physical nonlinearity of a real geological medium. The effects of higher harmonic generation and self-demodulation of signals are studied over a large range of distances from a source. A conclusion is that nonlinear properties of the medium should be taken into account in corresponding physical models used in seismology and seismic prospecting.