Geophysical Prospecting
SCIE-ISI SCOPUS (1953-2023)
0016-8025
1365-2478
Anh Quốc
Cơ quản chủ quản: WILEY , Wiley-Blackwell Publishing Ltd
Lĩnh vực:
GeophysicsGeochemistry and Petrology
Các bài báo tiêu biểu
Rapid least‐squares inversion of apparent resistivity pseudosections by a quasi‐Newton method1Abstract A fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer. This technique is based on the smoothness‐constrained least‐squares method and it produces a two‐dimensional subsurface model from the apparent resistivity pseudosection. In the first iteration, a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. For subsequent iterations, a quasi‐Newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times, respectively, compared to the conventional least‐squares method. Tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly. This technique takes about one minute to invert a single data set on an 80486DX microcomputer.
Tập 44 Số 1 - Trang 131-152 - 1996
Specific surface area and pore‐size distribution in clays and shalesABSTRACT One of the biggest challenges in estimating the elastic, transport and storage properties of shales has been a lack of understanding of their complete pore structure. The shale matrix is predominantly composed of micropores (pores less than 2 nm diameter) and mesopores (pores with 2–50 nm diameter). These small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore‐size distribution is critical to understand the shale pore network. Historically, mercury intrusion techniques are used for pore‐size analysis of conventional reservoirs. However, for unconventional shale reservoirs, very high pressures (> 414 MPa (60 000 psi)) would be required for mercury to access the full pore structure, which has potential pitfalls. Current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales. Nitrogen gas‐adsorption techniques can be used to characterize materials dominated by micro‐ and mesopores (2–50 nm). A limitation of this technique is that it fails to measure large pores (diameter >200 nm). We use a nitrogen gas‐adsorption technique to study the micro‐ and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques. Our results on pure clay minerals and natural shales show that (i) they have a multiscale pore structure at different dimensions (ii) fine mesopores, with a characteristic 3 nm pore size obtained with N2 gas‐adsorption are associated with an illite‐smectite group of clays but not with kaolinite; (iii) compaction results in a decrease of pore volume and a reduction of pore size in the ‘inter‐aggregate’ macropores of the illite‐smectite clays while the fine ‘intra‐tachoid’ mesopores are shielded from compaction; (iv) for natural shales, mineralogy controls the pore‐size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite‐smectite type of clays in the rock. Our assessment of incompressible 3 nm sized pores associated with illite‐smectite clays provides an important building block for their mineral modulus.
Tập 61 Số 2 - Trang 341-362 - 2013
Seismic wave extrapolation using lowrank symbol approximationABSTRACT We consider the problem of constructing a wave extrapolation operator in a variable and possibly anisotropic medium. Our construction involves Fourier transforms in space combined with the help of a lowrank approximation of the space‐wavenumber wave‐propagator matrix. A lowrank approximation implies selecting a small set of representative spatial locations and a small set of representative wavenumbers. We present a mathematical derivation of this method, a description of the lowrank approximation algorithm and numerical examples that confirm the validity of the proposed approach. Wave extrapolation using lowrank approximation can be applied to seismic imaging by reverse‐time migration in 3D heterogeneous isotropic or anisotropic media.
Tập 61 Số 3 - Trang 526-536 - 2013
MAPPING OIL‐CONTAMINATED SAND AND TILL WITH THE SPECTRAL INDUCED POLARIZATION (SIP) METHOD
Tập 45 Số 2 - Trang 303-326 - 1997
END CORRECTIONS IN POTENTIAL FIELD MODELING*Abstract A general treatment of end corrections in gravity and magnetic modeling is presented. The well‐known 2‐D formulae of Talwani and Talwani and Heirtzler become slightly changed to represent a 2 1/2–D body, i.e. a body of polygonal cross section with the tails In the strike direction cut off.
Tập 27 Số 4 - Trang 749-760 - 1979
CONTAMINATION INDICATIONS DERIVED FROM ELECTRICAL PROPERTIES IN THE LOW FREQUENCY RANGE1Abstract Electrical measurements are an important and integrated component of geophysical investigations connected with environmental problems. As a result of an analysis of the electrical conductivity, basic experiments on sandstones at frequencies below 10 kHz show that the complex behaviour of conductivity is caused exclusively by a complex interface conductivity. Its value is determined mainly by the internal rock interface to porosity ratio, the composition of the pore fluid and connected matrix‐water interactions resulting in a specific microstructure of the interface. Therefore, it can be expected that the interface region of a soil or rock material is very sensitive to changes in composition caused by contamination. Contaminated sandstone and clay samples were investigated using a low‐frequency measurement system. The investigations are directed at the influence of different contaminants and their concentration. Results show that the complex electrical conductivity (real and imaginary parts) is influenced by properties of the pore‐filling contaminant. This influence results in a change of the level of both parts and the shape of their frequency dependence. The imaginary part in particular seems to provide important secondary information; in some cases this part alone allows a differentiation of the various contaminants. The different behaviour of various rock types shows that the effects observed are the result of interactions between pore fluid properties and the internal pore surface structure.
Tập 41 Số 1 - Trang 83-98 - 1993
Approximating constant‐Q seismic propagation in the time domainABSTRACT In this study, we investigate the accuracy of approximating constant‐Q wave propagation by series of Zener or standard linear solid (SLS) mechanisms. Modelling in viscoacoustic and viscoelastic media is implemented in the time domain using the finite‐difference (FD) method. The accuracy of numerical solutions is evaluated by comparison with the analytical solution in homogeneous media. We found that the FD solutions using three SLS relaxation mechanisms as well as a single SLS mechanism, with properly chosen relaxation times, are quite accurate for both weak and strong attenuation. Although the RMS errors of FD simulations using a single relaxation mechanism increase with increasing offset, especially for strong attenuation (Q = 20), the results are still acceptable for practical applications. The synthetic data of the Marmousi‐II model further illustrate that the single SLS mechanism, to model constant Q , is efficient and sufficiently accurate. Moreover, it benefits from less computational costs in computer time and memory.
Tập 61 Số 5 - Trang 931-940 - 2013
A SIMULATED ANNEALING APPROACH TO SEISMIC MODEL OPTIMIZATION WITH SPARSE PRIOR INFORMATION1Abstract It is well known that seismic inversion based on local model optimization methods, such as iterative use of linear optimization, may fail when prior information is sparse. Where the seismic events corresponding to reflectors of interest remain to be identified, a global optimization technique is required. We investigate the use of a global, stochastic optimization method, that of simulated annealing, to solve the seismic trace inversion problem, in which the two‐way traveltimes and reflection coefficients are to be determined. The simulated annealing method is based on an analogy between the model‐algorithm system and a statistical mechanical system. We exploit this analogy to produce improved annealing schedules. It is shown that even in cases of virtually no prior information about two‐way traveltimes and reflection coefficients, the method is capable of producing reliable results.
Tập 39 Số 5 - Trang 599-611 - 1991
Effective permittivity of porous media: a critical analysis of the complex refractive index modelABSTRACT The availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi‐empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker‐Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker‐Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker‐Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore‐scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker‐Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data.
Tập 56 Số 5 - Trang 715-727 - 2008