Table of contents

The resistivity method is frequently used in the investigation of the shallow parts of the earth. Interpretation of such data is usually done assuming a layered earth. However, a more complete imaging can be obtained if 3D models are used. Thirty-five vertical electrical soundings (VES) were carried out in a regular mesh at the northwestern part of Greater Cairo in order to characterize different geological units and to study their quality for building foundations. Models obtained from 1D inversion of each VES, together with borehole information, were used for construction of eight geoelectrical sections which exhibit the main geoelectrical characteristics of the geological units present in the area. The 3D inversion of the data indicated a complex subsurface electrical resistivity distribution conditioned by lithology, water content and tectonic structures. The results indicate that the subsurface consists of different geologic units such as gravel and sand, sand, clay and limestone. The main results are related to the characterization of the clay formations in the north of the survey area, which is revealed by low-resistivity values (<100 Ω m) and sand layers associated with high-resistivity values (>600 Ω m) depicted in the central part of the study zone.

Log data are of prime importance in acquiring petrophysical data from hydrocarbon reservoirs. Reliable log analysis in a hydrocarbon reservoir requires a complete set of logs. For many reasons, such as incomplete logging in old wells, destruction of logs due to inappropriate data storage and measurement errors due to problems with logging apparatus or hole conditions, log suites are either incomplete or unreliable. In this study, fuzzy logic and artificial neural networks were used as intelligent tools to synthesize petrophysical logs including neutron, density, sonic and deep resistivity. The petrophysical data from two wells were used for constructing intelligent models in the Fahlian limestone reservoir, Southern Iran. A third well from the field was used to evaluate the reliability of the models. The results showed that fuzzy logic and artificial neural networks were successful in synthesizing wireline logs. The combination of the results obtained from fuzzy logic and neural networks in a simple averaging committee machine (CM) showed a significant improvement in the accuracy of the estimations. This committee machine performed better than fuzzy logic or the neural network model in the problem of estimating petrophysical properties from well logs.

A three-dimensional finite element method is proposed and used to deal with large-scale nonlinear contact friction problems in deformable rocks. Together with the use of the node-to-point contact element strategy, the corresponding three-dimensional finite element algorithm is presented to simulate the nonlinear contact friction behaviour between deformable rock blocks. In order to ensure the correctness and accuracy of the resulting numerical solutions, the proposed finite element formulation for a three-dimensional nonlinear contact friction problem is verified using a benchmark problem, for which the analytical solution is available. As an application example, the proposed three-dimensional finite element method is used to investigate the plate behaviour of a subduction fault model, which simulates a region around Northeast Japan. Due to the general nature of the methodology, the proposed three-dimensional finite element algorithm can be also used to simulate many nonlinear contact friction problems associated with the slope instability process and the sliding failure mechanism between a gravity dam and its foundation in the engineering field.

In this paper, we introduce a formula for extracting Lame's parameters (λ and μ) in a VTI medium. We show the application of the inversion method to this formula for extracting reflection coefficients of P- and S-wave velocities in a VTI medium. Finally, we show the application of this method to a carbonate reservoir in South West Iran. Results of this research indicate that, if anisotropy parameters are used in steps while extracting λ and μ, we can distinguish between reservoir zones with different lithology and fluid content.

This paper presents an application of a 3D numerical model to simulate one vertical layer sediment transport and coastal morphodynamical process for the Hai Hau coastal area located in the north of Vietnam, where a very large amount of suspended sediment is carried into the sea from Ba Lat Mouth every year. Four simulations are based on the real data of waves supplied by the observation station close to Ba Lat Mouth. The conditions of wind and suspended sand concentration at Ba Lat Mouth are basically assumed from practice. The computed results show that the hydrodynamic factors strongly depend on the wind condition and these factors govern the direction and the range of suspended sand transport, especially in the shallow-water region. In the deep-water region this influence is not really clear when the wind force is not strong enough to modify the tidal current. In the area close to Ba Lat Mouth the flow velocity is very large with the maximum flood flow about 2.6 m s⁻¹ and the maximum ebb flow about 1 m s⁻¹ at the mouth, and this is one of the reasons for strong erosion. In the case of tidal flow only, the suspended sand concentration decreases resulting in local deposition. Therefore, the area influenced by suspended transport is small, about 12 km from the mouth. In the condition of wind and waves, the suspended sand transport reaches the end of the computation area within a few days, especially the cases with wind from the north-east-north. Through these simulation results, a common tendency of sediment movement from the north to the south is specified for the Hai Hau coastal area. In addition, the results also show that the coast suffers from strong erosion, especially the region near Ba Lat Mouth. From the simulation results it can be seen that the movement of the Red River sand along the Vietnamese coast is quite possible, which is an answer to a long-standing question. Furthermore, although the suspended sediment concentration is quite large, it is still not enough to compensate for the strong erosion of the Ba Lat Mouth region.

Saturation and pore pressure changes within a reservoir can be estimated by a history matching process based on production data. If time-lapse seismic data are available, the same parameters might be estimated directly from the seismic data as well. There are several ways to combine these data sources for estimating these reservoir parameters. In this work, we formulate a nonlinear inversion scheme to estimate pressure and saturation changes from time-lapse seismic data. We believe that such a formulation will enable us to include seismic data in the reservoir simulator in an efficient way, by including a second term in the least- squares objective function. A nonlinear Gauss–Newton inversion method is tested on a 2D synthetic dataset inspired by a field offshore from Norway. A conventional reservoir simulator has been used to produce saturation and pore pressure changes as a function of production time. A rock physics model converts these data into synthetic time-lapse seismic data. Finally, the synthetic time-lapse data are used to test the derived inversion algorithm. We find that the inversion results are strongly dependent on the input model, and this is expected since we are dealing with an ill-posed inversion problem. Since we estimate pressure and saturation change for each grid cell in the reservoir model, the number of model parameters is high, and therefore the problem is undetermined. From testing, using this particular dataset, we assume neither pressure nor saturation changes for the initial model. Although uncertainties associated with the proposed method are high, we think this might be a useful tool, since there are ways to reduce the number of model parameters and constrain the objective function by including production data and reservoir simulation data into this algorithm.

The 3D geoelectric probability tomography method has been previously developed as a powerful approach to localize in the subsoil the sources of the apparent resistivity anomalies detected on the ground surface. We show that this method can be successfully applied in the archaeological park of Pompei to recognize buried remains of the ancient Roman urbanization including roads, squares and buildings which were heavily damaged and totally buried under a thick cover of volcanic fall products resulting from the well-known disastrous 79 AD Vesuvius eruption. A further development is made in this work concerning the identification of source poles and dipoles underground, ascribable to the physical centre of the bodies with anomalous resistivity and to their boundaries, respectively. Different imaging systems are used to enhance the quality of information derived from the tomography analysis.

The influence of spread and shot systems is investigated using common measuring geometries like conventional crosshole and multi-offset VSP. Both synthetic and field data are used to understand better the importance of commonly used spread and shot systems in the image reconstruction process. In the synthetic case, a faulted structure under a near-surface low velocity layer is used. The results of the seismic images compared with the original model and the similarities in the structure and in the velocities are investigated. Tomograms derived from the real data are compared with ground truth. Our study shows that realistic spread systems can produce nearly the same quality images as in the ideal ones.

At present when conducting an interference well test a constant flow rate (at the 'active' well) is utilized and the type-curve matching technique (where only 2–3 values of pressure drops are matched) is used to estimate the porosity–total compressibility product and formation permeability. For oil and geothermal reservoirs with low formation permeability the duration of the test may require a long period of time and it can be difficult to maintain a constant flow rate. The qualitative term 'long' period of time means that (at a given distance between the 'active' and 'observational' well) more test time (for low permeability formations) is needed to obtain tangible pressure drops in the 'observational' well. In this study we present working equations which will allow us to process field data when the flow rate at the 'active' well is a function of time. The shut-in period is also considered. A new method of field data processing, where all measured pressure drops are utilized, is proposed. The suggested method allows us to make use of the statistical theory to obtain error estimates on the regression parameters. It is also shown that when high precision (resolution) pressure gauges are employed the pressure time derivative equations can be used for the determination of formation hydraulic diffusivity. An example is presented to demonstrate the data processing procedure.

In this paper, we present an example of using PP and PS converted-wave data recorded by digital micro-eletro-mechanical-systems (MEMS) to evaluate a fractured tight gas reservoir from the Xinchang gas field in Sichuan, China. For this, we analyse the variations in converted shear-wave splitting, Vp/Vs ratio and PP and PS impedance, as well as other attributes based on absorption and velocity dispersion. The reservoir formation is tight sandstone, buried at a depth of about 5000 m, and the converted-wave data reveal significant shear-wave splitting over the reservoir formation. We utilize a rotation technique to extract the shear-wave polarization and time delay from the data, and a small-window correlation method to build time-delay spectra that allow the generation of a time-delay section. At the reservoir formation, the shear-wave time delay is measured at 20 ms, about 15% shear-wave anisotropy, correlating with the known gas reservoirs. Furthermore, the splitting anomalies are consistent with the characteristics of other attributes such as Vp/Vs ratio and P- and S-wave acoustic and elastic impedance. The P-wave shows consistent low impedance over the reservoir formation, whilst the S-wave impedance shows relatively high impedance. The calculated gas indicator based on absorption and velocity dispersion yields a high correlation with the gas bearing formations. This confirms the benefit of multicomponent seismic data from digital MEMS sensors.

In terms of elastic anisotropy, sedimentary shales may be considered to have transverse symmetry. Experimentally determining the five independent elastic constants required for this case remains challenging. This paper proposes the use of ultrasonic waves in determination of the five constants. Arrays of specially constructed transducers with different modes of vibration were mounted on samples trimmed from natural cores to measure ultrasonic P-waves and S-waves along the horizontal, vertical and 45°-inclination axes on the samples. The elastic constants calculated from these wave velocities were compared to those determined from static tests and acoustic in situ logs. The static tests included drained triaxial compression and confined torsion tests. The acoustic logs were conducted in an open hole using monopole compressional and dipole shear transmitters and receivers. It was found that the elastic constants determined by the static tests were much lower than those determined from the ultrasonic tests and acoustic logs. Discrepancies among the elastic constants determined from these three different methods are discussed and explained.

We investigate the enhanced deconvolution of transmitted seismic waves from distant natural sources using autoregressive extrapolation (AR) and extended time-domain deconvolution. The amplitude spectrum of deconvolved seismograms is often restricted to a reduced frequency range from the use of a water table for the deconvolution. The attenuation effects on the teleseismic seismic waves also reduce the frequency content of the data. We compare the deconvolved spectra obtained from an AR-extended deconvolution (EARD) and an extended time-domain deconvolution (ETDD) technique for teleseismic waves. For EARD, we analyse the spectral content for the deconvolved spectra to differentiate between the domains of known and unknown spectral values. A prediction error filter is used to perform the autoregressive extrapolation to estimate the unknown spectral values. This procedure is applied on 1D and 2D synthetic data to test the approach. The EARD approach is then compared with the ETDD approach which applies an extended high-pass filter to the time-domain deconvolution approach. Both the EARD and ETDD approaches for extending the effective frequency range of the deconvolution results are then compared using observed teleseismic data recorded in southern India.