Vladimir Shevnin

Separation of anisotropy and inhomogeneity influence by the spectral analysis of azimuthal resistivity diagrams

The first aim of resistivitv survey is a study of any inhomogeneities. Frequently in practice the effect of anisotropy is displayed together with that of layering or inhomogeneities. It complicates data interpretation within the framework of anisotropic models, and distorts results of interpretation in the framework of layered or inhomogeneous media.

Investigations of oil pollution with electrical prospecting methods

The most widespread source of pollution in Russia is the oil pollution. It occurs at all stages of oil production, transportation and processing. Outflows, proceeding during decades result to formation of oil secondary deposits.

Anisotropy Determination In Heterogeneous Media By Tensor Measurements of the Electric Field

Traditional anisotropic resistivity survey requires performing a set of azimuthal measurements. In an anisotropic heterogeneous medium the possibility of an anisotropy study is restricted by the necessity to carry out the time-consuming azimuthal soundings on a dense grid of observations. On the other hand, at applying the Electrical Imaging in anisotropic media the complete neglect of azimuthal−anisotropy influence can result in noticeable errors of interpretation. The authors propose an alternative method to determine the parameters of anisotropic media based on measuring the second derivatives of the electric potential from a point current source. Such a technology (named tensor measurements) reduces a number of observation azimuths to a single one and at the same time allows obtaining all anisotropy parameters. The efficiency of different tensor arrays is illustrated on the complex 3D model of the dipping interface between an isotropic overburden and an anisotropic basement. In this case the effects produced by anisotropy, heterogeneity, and formation layering appear jointly. The vertical soundings with the tensor measurements give three apparent characteristics: mean resistivity ρam, anisotropy coefficient λa, and anisotropy strike αa. The interpretation of their cross-sections allows determining true parameters of anisotropy and structure.

Anisotropy Effects Investigations by Resistivity Method in Some Inhomogeneous Media

Resistivity method is usually applied for horizontally-layered media investigation as sounding, and for inhomogeneous media as profiling.

ESTIMATION OF SOIL HYDRAULIC CONDUCTIVITY ON CLAY CONTENT, DETERMINED FROM RESISTIVITY DATA

We considered clay content in loose soil as the factor mostly influencing on hydraulic conductivity (filtration coefficient). We collected and analyzed some published experimental data about hydraulic conductivity relation with soil lithology and clay content in the form of grain size. Also we performed some theoretical modeling modifying well-known formulas to include clay content in them. Experimental and calculated data showed quite good coincidence. Correlation between hydraulic conductivity and clay content seemed better, than correlation between hydraulic conductivity and resistivity. We created some approximation formulas relating filtration coefficient with clay content. Clay content in soil can be estimated on soil resistivity obtained from VES data interpretation and from groundwater salinity found from its resistivity. Then filtration coefficient is determined on clay content. Some examples of this method practical application at clean and oil contaminated areas are presented. We considered anomalies of decreasing filtration coefficient in contaminated zones not as a real effect, but as a good indicator of contamination, though in several publications there were some indications of hydro geological changes in soil properties due to oil contamination.

Pipelines' studies -- new problem for geophysics

The modern technical civilization creates the advanced network of subterranean communications. From the centurys beginning many thousand kilometers of various pipes and cables were stacked in ground on depth up to 5-6 meters. Their large part concentrates in cities. Among these there are communications lines, electrical power cables, water, oil and gas tubes, heat-conducting, water drain and waste water pipes. Especially large density of the communications achieves at territory of industrial plants. This network of pipes and cables creates artificial (technogenic) medium, which requires the constant control. At installation of pipes and cables their position is reflected in documents, however in time some engineering specification becomes outdated or even lost.

Distortions of VES data caused by subsurface inhomogeneities

The first (mainly used) model for VES method is based on horizontally layered structure. The second one includes different deep objects, such as faults, horsts, grabens, domes, etc. We introduce the third model, which includes horizontal layers, deep objects, and many subsurface objects of different resistivities, referred to as subsurface inhomogeneities (SSIs).

ELECTROMAGNETIC SURFACE METHOD FOR THE PIPELINE PERIODICAL INSPECTION BASED ON THE HETEROGENEOUS TRANSMISSION LINE MODEL

The superficial electromagnetic methods are widely applied for non-destructive control of pipeline technical condition. For this purpose we have developed the theory and field technology for the pipeline inspection that allows: 1) determining the pipeline trajectory (plane position and depth), 2) delimitation of pipeline intervals with an insulation coating damage, and 3) estimating the condition of a cathodic protection system. The proposed method is based on the approximation of a metallic pipeline by a heterogeneous transmission line with variable distributed parameters: resistance and inductance along a tube (tube wall thickness) and leakage conductance. The field operations consist in measurements of magnetic field above a pipeline and voltage only on the control posts. The interpretation process includes the iterative inversion of the magnetic component in order to determine the pipeline depth and current distribution along pipeline. The current difference corresponds to leakage current and allow estimate the leakage resistance. We illustrate the practical application of this method using the obtained results for pipeline inspections in Mexico. Based on the voltage and current simulations for the infralowfrequency band (0-1kHz) we have evaluated the feasibility of the time lapse measurements of the magnetic field in some fixed points for the early prediction of an insulation damaging process.

Arrays for Tensor Measurements of the Electric Field

The study of resistivity anisotropy in heterogeneous media is a complex problem that needs developing the special field technology and interpretation technique. Traditional anisotropic resistivity survey requires performing a set of azimuthal measurements. In the case of the anisotropy estimation in heterogeneous media the application of such a technology is essentially restricted by the field-operating complexity for profiling and sounding. On the other hand, at applying the Electrical Resistivity Tomography (ERT) in anisotropic media the neglect of azimuthal−anisotropy influence can result in noticeable errors of interpretation. The alternative method of anisotropy determination is based on measuring the second derivatives of the electric potential from a point current source. This technology consists in the tensor measurements of the electric field using groups of specially distributed transmitting and receiving electrodes (tensor arrays). The tensor measurements allow obtaining the orientation and value of the resistivity anisotropy from the observations realized for a single orientation of the array without its rotation. In this report we analyzed the feasibility of different modifications of the tensor array for the determination of anisotropy parameters and their field applicability for profiling and sounding. The sensitivity and stability of the anisotropy estimation with the tensor arrays were shown for a horizontally layered anisotropic medium and vertical anisotropic layer in an isotropic half-space.

A New Approach to Resistivity Anisotropy Measurements

Summary This work introduces a new approach for the estimation of resistivity anisotropy parameters from measurements of the second electrical potentials derivatives. This approach allows to estimate anisotropy parameters by measuring on a single arbitrary azimuth instead of traditional azimuthal resistivity survey. Stability of anisotropy parameters’ estimation from the second potentials derivatives and opportunities of new technology application for resistivity profiling and sounding are shown at several models of inhomogeneous anisotropic media.