In the last 30 days

• Open/close Relationships between permeability, porosity and pore throat size in carbonate rocks using regression analysis and neural networks

  M R Rezaee et al 2006 J. Geophys. Eng. 3 370 Tag this article

  Article References Full text PDF (207 KB)

  Accurate estimation of permeability from other data has been a challenge for many years. The aim of this study was to establish relationships between permeability, porosity and pore throat size, and apply these relationships in a predictive sense. Regression analysis was utilized to achieve a set of relationships between permeability, porosity and pore throat size for 144 carbonate samples. These relationships can be used to estimate permeability from porosity and pore throat radii. Also in this study, a fully-connected multi-layer perceptron network was used to predict permeability from porosity and pore throat radii. An artificial neural network, a biologically inspired computing method which has an ability to learn, self-adjust, and be trained, provides a powerful tool in solving complex problems. These characteristics have enabled artificial neural networks to be more successful in predicting permeability when compared to regression analysis.

  This study also indicates that pore throat radii corresponding to a mercury saturation of 50% (r ₅₀) is the best permeability predictor for carbonates with complex pore networks.

• Open/close A practical implicit finite-difference method: examples from seismic modelling

  Yang Liu and Mrinal K Sen 2009 J. Geophys. Eng. 6 231 Tag this article

  Article References Full text PDF (2.76 MB)

  We derive explicit and new implicit finite-difference formulae for derivatives of arbitrary order with any order of accuracy by the plane wave theory where the finite-difference coefficients are obtained from the Taylor series expansion. The implicit finite-difference formulae are derived from fractional expansion of derivatives which form tridiagonal matrix equations. Our results demonstrate that the accuracy of a (2 N + 2)th-order implicit formula is nearly equivalent to that of a (6 N + 2)th-order explicit formula for the first-order derivative, and (2 N + 2)th-order implicit formula is nearly equivalent to (4 N + 2)th-order explicit formula for the second-order derivative. In general, an implicit method is computationally more expensive than an explicit method, due to the requirement of solving large matrix equations. However, the new implicit method only involves solving tridiagonal matrix equations, which is fairly inexpensive. Furthermore, taking advantage of the fact that many repeated calculations of derivatives are performed by the same difference formula, several parts can be precomputed resulting in a fast algorithm. We further demonstrate that a (2 N + 2)th-order implicit formulation requires nearly the same memory and computation as a (2 N + 4)th-order explicit formulation but attains the accuracy achieved by a (6 N + 2)th-order explicit formulation for the first-order derivative and that of a (4 N + 2)th-order explicit method for the second-order derivative when additional cost of visiting arrays is not considered. This means that a high-order explicit method may be replaced by an implicit method of the same order resulting in a much improved performance. Our analysis of efficiency and numerical modelling results for acoustic and elastic wave propagation validates the effectiveness and practicality of the implicit finite-difference method.

• Open/close Representation of the thickness distribution of channels and stratigraphic events at one of the Iranian fields in the Hormuz Strait using a composite plot and RGB display technique

  M R Saadatinejad et al 2011 J. Geophys. Eng. 8 412 Tag this article

  Article References Full text PDF (3.36 MB)

  The Hormuz Strait is an important area which is located between the Persian Gulf, with half the oil reserves of the world, and the Oman Sea south of Iran. Many geophysical studies have been done to analyse the structure of subsurface layers in this strait and explore many new gas reservoirs as these findings help to simulate images from reservoir stratigraphy and understand the paleo-depositional environments. Spectral decomposition, which is a quick and important method in seismic interpretation, provides a strong tool to study these types of subsurface layers. In this paper, a red–green–blue (RGB) multi-colour display technique has been performed as an effective interpretation tool. This technique stacks three different frequencies with three different colours for composite display. So, these frequency components show the distribution of channel thickness as we map the variation of thickness with a colour scale that is equal to the quantitative thickness according to its relationship with frequency. In addition, seismic attributes such as coherency, peak and instantaneous frequency, which are sensitive to the edges of stratigraphic events (such as channels), are shown with a composite plot too; although the RGB technique is better than other techniques, for thickness variation a combined application is the best method of study.

• Open/close Comparison of Wenner and dipole–dipole arrays in the study of an underground three-dimensional cavity

  Ahmad Neyamadpour et al 2010 J. Geophys. Eng. 7 30 Tag this article

  Article References Full text PDF (4.26 MB)

  The objective of this paper was to compare Wenner and dipole–dipole configurations in delineating an underground cavity at a site near the University of Malaya, Malaysia. A three-dimensional electrical resistivity imaging survey was carried out along seven parallel lines using Wenner and dipole–dipole arrays. A three-dimensional least-squares algorithm, based on the robust inversion method, was used in the inversion of the apparent resistivity data. In the inverted model, both the horizontal and vertical extents of the anomalous zones were displayed. Results indicate the superiority of the Wenner array over the dipole–dipole array for determining the vertical distribution of the subsurface resistivity, although the dipole–dipole array produced a better lateral extent of the subsurface features. The results show that the three-dimensional electrical resistivity imaging survey using both the Wenner and dipole–dipole arrays, in combination with an appropriate three-dimensional inversion method and synthetic model analysis, can be highly useful for engineering and environmental applications, especially for underground three-dimensional cavity detection.

• Open/close Statistical correlations of shear wave velocity and penetration resistance for soils

  Ünal Dikmen 2009 J. Geophys. Eng. 6 61 Tag this article

  Article References Full text PDF (3.69 MB)

  In this paper, the correlation between shear wave velocity and standard penetration test blow counts (SPT- N) is investigated. The study focused primarily on the correlation of SPT- N and shear wave velocity ( V _s) for several soil categories: all soils, sand, silt and clay-type soils. New empirical formulae are suggested to correlate SPT- N and V _s, based on a dataset collected in a part of Eskişehir settlement in the western central Anatolia region of Turkey. The formulae are based on geotechnical soundings and active and passive seismic experiments. The new and previously suggested formulae showing correlations between uncorrected SPT- N and V _s have been compared and evaluated by using the same dataset. The results suggest that better correlations in estimation of V _s are acquired when the uncorrected blow counts are used. The blow count is a major parameter and the soil type has no significant influence on the results. In cohesive soils, the plasticity contents and, in non-cohesive soils except for gravels, the graded contents have no significant effect on the estimation of V _s. The results support most of the conclusions of earlier studies. These practical relationships developed between SPT- N and V _s should be used with caution in geotechnical engineering and should be checked against measured V _s.

• Open/close A new algorithm for gravity or self-potential data interpretation

  Khalid S Essa 2011 J. Geophys. Eng. 8 434 Tag this article

  Article References Full text PDF (550 KB)

  An inversion algorithm is developed to estimate the depth and the associated model parameters of the anomalous body from the gravity or self-potential (SP) whole measured data. The problem of the depth ( z) estimation from the observed data has been transformed into a nonlinear equation of the form F( z) = 0. This equation is then solved for z by minimizing an objective functional in the least-squares sense. Using the estimated depth, the polarization angle and the dipole moment or the depth and the amplitude coefficient are computed from the measured SP or gravity data, respectively. The method is based on determining the root mean square (RMS) of the depths estimated from using all s-values for each shape factor. The minimum RMS is used as a criterion for estimating the correct shape and depth of the buried structure. When the correct shape factor is used, the RMS of the depths is always less than the RMS computed using wrong shape factors. The proposed approach is applicable to a class of geometrically simple anomalous bodies, such as the semi-infinite vertical cylinder, the dike, the horizontal cylinder and the sphere, and it is tested and verified on synthetic examples with and without noise. This technique is also successfully applied to four real datasets for mineral exploration, and it is found that the estimated depths and the associated model parameters are in good agreement with the actual values.

• Open/close New modelling of transient well test and rate decline analysis for a horizontal well in a multiple-zone reservoir

  Ren-Shi Nie et al 2011 J. Geophys. Eng. 8 464 Tag this article

  Article References Full text PDF (1.59 MB)

  The no-type curve with negative skin of a horizontal well has been found in the current research. Negative skin is very significant to transient well test and rate decline analysis. This paper first presents the negative skin problem where the type curves with negative skin of a horizontal well are oscillatory. In order to solve the problem, we propose a new model of transient well test and rate decline analysis for a horizontal well in a multiple-zone composite reservoir. A new dimensionless definition of r _D is introduced in the dimensionless mathematical modelling under different boundaries. The model is solved using the Laplace transform and separation of variables techniques. In Laplace space, the solutions for both constant rate production and constant wellbore pressure production are expressed in a unified formula. We provide graphs and thorough analysis of the new standard type curves for both well test and rate decline analysis; the characteristics of type curves are the reflections of horizontal well production in a multiple-zone reservoir. An important contribution of our paper is that our model removed the oscillation in type curves and thus solved the negative skin problem. We also show that the characteristics of type curves depend heavily on the properties of different zones, skin factor, well length, formation thickness, etc. Our research can be applied to a real case study.

• Open/close Porosity and permeability estimation by integration of production and time-lapse near and far offset seismic data

  Mohsen Dadashpour et al 2009 J. Geophys. Eng. 6 325 Tag this article

  Article References Full text PDF (2.97 MB)

  This study presents a method based on the Gauss–Newton optimization technique for continuous reservoir model updating with respect to production history and time-lapse seismic data in the form of zero offset amplitudes and amplitude versus offset (AVO) gradients. The main objective of the study is to test the feasibility of using these integrated data as input to reservoir parameter estimation problems. Using only production data or zero offset time-lapse seismic amplitudes as observation data in the parameter estimation process cannot properly limit the solution space. The emphasis of this work is to use the integrated data combined with empirical knowledge about rock types from laboratory measurements, to further constrain the inversion process. The algorithm written for this study consists of three parts: the reservoir simulator, the rock physics petro-elastic model and the optimization algorithm. The Gauss–Newton inversion is tested at a 2D semi-synthetic model inspired by real field data from offshore Norway. The algorithm reduces the misfit between the observed and simulated data which make it possible to estimate porosity and permeability distributions. The Gauss–Newton optimization technique is an efficient parameter estimation technique. However, the numerical estimation of the gradient is time consuming, and it can be prohibitive for practical applications. This method is suitable for distributed computing which considerably reduces the total optimization time. The amount of reduction depends mainly on the number of available processors.

• Open/close Noise suppression based on a fast discrete curvelet transform

  Zhi-yu Zhang et al 2010 J. Geophys. Eng. 7 105 Tag this article

  Article References Full text PDF (1.92 MB)

  A curvelet transform (CT) is a new kind of multi-scale analysis algorithm which is more suitable for image processing; as compared with a wavelet transform (WT), it can better analyse the line and curve edge characteristics, and it has better approximation precision and sparsity description and also has good directivity. This paper introduces ground roll suppression of a seismic signal based on a fast discrete curvelet transform (FDCT) and the direct wave removal in ground penetrating radar (GPR) based on a CT. A ground roll is an interferential wave existing widely in seismic data, and it is an important step in seismic data processing to suppress ground roll. The method can separate the different waves at the same time because of CT characteristics of frequency and direction. In the ground penetrating radar signal, the direct wave is a strong noise which has line singularity. In the time-space domain, the useful information in the GPR signal is badly polluted by a strong direct wave so that the underground objects cannot be recognized correctly. The FDCT is employed to remove the background noise and separate the direct wave. The experimental results show that a CT has better effects in ground-roll suppression and direct wave removal.

• Open/close A fuzzy logic approach for estimation of permeability and rock type from conventional well log data: an example from the Kangan reservoir in the Iran Offshore Gas Field

  Ali Kadkhodaie Ilkhchi et al 2006 J. Geophys. Eng. 3 356 Tag this article

  Article References Full text PDF (4.47 MB)

  Permeability and rock type are the most important rock properties which can be used as input parameters to build 3D petrophysical models of hydrocarbon reservoirs. These parameters are derived from core samples which may not be available for all boreholes, whereas, almost all boreholes have well log data. In this study, the importance of the fuzzy logic approach for prediction of rock type from well log responses was shown by using an example of the Vp to Vs ratio for lithology determination from crisp and fuzzy logic approaches. A fuzzy c-means clustering technique was used for rock type classification using porosity and permeability data. Then, based on the fuzzy possibility concept, an algorithm was prepared to estimate clustering derived rock types from well log data. Permeability was modelled and predicted using a Takagi-Sugeno fuzzy inference system. Then a back propagation neural network was applied to verify fuzzy results for permeability modelling. For this purpose, three wells of the Iran offshore gas field were chosen for the construction of intelligent models of the reservoir, and a forth well was used as a test well to evaluate the reliability of the models. The results of this study show that fuzzy logic approach was successful for the prediction of permeability and rock types in the Iran offshore gas field.