A Walsh sequency filtration method for integrating the resistivity log and sounding data

Geophysics ◽  
1991 ◽  
Vol 56 (8) ◽  
pp. 1259-1266 ◽  
Author(s):  
Poorna C. Pal
Keyword(s):  
Electrical Resistivity ◽  
Apparent Resistivity ◽  
Groundwater Exploration ◽  
Walsh Functions ◽  
Filtration Method ◽  
Resistivity Logs ◽  
Logarithmic Scaling ◽  
Input Model ◽  
Resistivity Log

The integration of resistivity logs and soundings data, essential for resolving the problems of ambiguity and nonuniqueness ubiquitous in the interpretation of electrical resistivity soundings, is generally difficult because the former contain far more details than can be retrieved from the latter. As logarithmic scaling linearizes the behavior of apparent resistivity values and resistivity transform functions, and as the Walsh functions realistically mimic the resistivity logs, the strategy proposed here is to use the resistivity‐stratigraphy schematized from Walsh‐filtration of logarithmically scaled logs‐profile as input model for sounding interpretation. The efficiency of this strategy is demonstrated here with a practical example from groundwater exploration. The synthetic sounding curve based on 29 layers manually schematized from the observed linearly scaled logs‐profile could be modeled by 8 layers, whereas that computed from 14 layers schematized from sequency‐filteration of the logarithmically scaled logs‐profile closely matched the observed sounding curve from a nearby location.

SALT BED IDENTIFICATION FROM UNFOCUSED RESISTIVITY LOGS

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 320-341
Author(s):  
J. R. Lishman
Keyword(s):  
Electrical Resistivity ◽  
Apparent Resistivity ◽  
Borehole Diameter ◽  
Drilling Fluids ◽  
Characteristic Shape ◽  
Resistivity Logs

Salt beds have almost infinite electrical resistivity. They differ from other infinitely resistive beds in that they are usually soluble in drilling fluids, and give rise to enlarged boreholes. An infinitely resistive bed lying between shales may be recognized from the characteristic shape of the electric log resistivity curves, and the ratios of their readings. Any one of the curves may then be used to compute the borehole diameter, and hence decide whether the bed is salt. Where a washed out salt bed is adjacent to another infinitely resistive bed in which the borehole is to gauge, the configuration of the curves is very characteristic. Apparent resistivity ratios again help to identify the salt.

THE USE OF THERMAL RESISTIVITY LOGS IN STRATIGRAPHIC CORRELATION

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 300-309 ◽  
Author(s):  
A. E. Beck
Keyword(s):  
Electrical Resistivity ◽  
Temperature Gradients ◽  
Thermal Resistivity ◽  
Stratigraphic Correlation ◽  
Resistivity Logs ◽  
Precision Temperature ◽  
Order Of Magnitude ◽  
The Mean ◽  
Resistivity Log ◽  
Gas Bearing

Since it has been found that the heat flow along a borehole rarely deviates more than 20 percent from the mean equilibrium value and that formation thermal resistivities may vary by as much as an order of magnitude, the profile of temperature gradient versus depth is equivalent to a log of thermal resistivity (T-log). In this work high precision temperature measurements in cased boreholes were used which yielded temperature gradients as high as 140°C/km. Using the equivalence between thermal resistivity and temperature gradients, it has been found that the T-logs are characteristic of the formations in which they were measured with a general negative correlation between thermal resistivity and electrical resistivity, except in coal (and perhaps gas) bearing formations. In one instance, the character of the resistivity log was used to conclude that a horizon deduced from the electrical resistivity log had been mispicked by nearly 100 m.

Sand injectite mapping using a resistivity-velocity transform function

2021 ◽  
Vol 40 (3) ◽  
pp. 202-207
Author(s):  
Anke S. Wendt ◽  
Monzurul Alam ◽  
Joao Paulo Castagnoli
Keyword(s):  
Residual Velocity ◽  
Rock Types ◽  
Geostatistical Approach ◽  
Spatially Distributed ◽  
Resistivity Logs ◽  
Hydrocarbon Fields ◽  
Interval Velocities ◽  
Resistivity Log ◽  
Measured Resistivity ◽  
Sand Bodies

Lack of resolution in the distribution of sand injectites in hydrocarbon fields is common and makes it difficult to predict drilling challenges and plan for optimum production. A practical workflow was developed that enables the distinction of shale and sand bodies by using a combination of low-resolution seismic data and high-resolution resistivity log data. Measured resistivity logs were used to predict synthetic velocity logs, which accurately match shale velocities and over- or underestimate velocities of other rock types. The synthetic velocity logs were spatially distributed in a 3D cube in order to predict synthetic velocities in between and away from the well locations. The 3D cube was representative of a field. It covered the interval from the seabed to below the reservoir. The spatial distribution was based on a geostatistical approach guided by measured seismic interval velocities. A residual velocity cube was calculated from the measured and synthetic velocities. The residual velocity cube produced near-zero velocities for shaly materials and velocity over- or underestimates for other rock types. Interpretation of the residual velocity cube required the identification of strong stratigraphic markers. The markers were removed from the residual cube by setting their specific layer velocities to 0 m/s. The final information stored in the residual velocity cube was then related to the over- or underestimated velocities in sand bodies.

scholarly journals Electrical Resistivity Profiles and Temperatures in the Ross Ice Shelf

1976 ◽  
Vol 16 (74) ◽  
pp. 307-308
Author(s):  
C.R. Bentley
Keyword(s):  
Electrical Resistivity ◽  
Computer Program ◽  
Depth Profile ◽  
Apparent Resistivity ◽  
Ice Shelf ◽  
Resistivity Measurements ◽  
Ross Ice Shelf ◽  
Field Season ◽  
A Site ◽  
Temperature Depth

AbstractDuring the 1973-74 Antarctic field season, two electrical resistivity profiles were completed along directions perpendicular to each other at a site in the south-easternpart of the Ross Ice Shelf. These profiles differ from each other only at short electrode spacings (less than 10 m) indicating no measurable horizontal anisotropy below the uppermost firn zone. The shape of the apparent resistivity curves is similar to that found by Hochstein on the Ross Ice Shelf near Roosevelt Island, but is displaced toward lower resistivities despite the colder 10 m temperature (—29°C instead of —26°C) at the more southerly site. Some factor other than temperature must therefore be effective in determining the overall magnitude of the resistivities in the shelf, although the variation with depth can still be expected to be primarily a temperature phenomenon.A computer program has been written to calculate apparent resistivities based on Crary’s analysis of temperatures in an ice shelf. Results are not yet available; when completed they should indicate the sensitivity of the resistivity measurements to differences in the temperature- depth profile, and hence their usefulness in estimating bottom melt/freeze rates.

A combination of electrical resistivity, seismic refraction, and gravity measurements for groundwater exploration in Sudan

Geophysics ◽  
1981 ◽  
Vol 46 (9) ◽  
pp. 1304-1313 ◽  
Author(s):  
Ronald A. van Overmeeren
Keyword(s):  
Electrical Resistivity ◽  
Seismic Refraction ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Equivalence Problem ◽  
Groundwater Exploration ◽  
Fresh Groundwater ◽  
Subsequent Test ◽  
Additional Information ◽  
Electrical Sounding

In the savannah belt of central Sudan, near the town of Kosti, a regional geophysical survey has been carried out forming part of a groundwater project. Because of the presence of detectable and significant contrasts in physical properties of the subsoil, integrated use could be made of electrical resistivity, seismic refraction, and gravity methods. In the interpretation of multilayer electrical sounding curves, additional subsurface information such as lithological well descriptions and geophysical well logs is normally a necessity for solving the problems of equivalence. Along a profile in the eastern part of the area studied, where additional subsurface information was scarce, 16 vertical electrical soundings have been made. A preliminary simple mathematical interpretation suggested possibilities for the presence of fresh groundwater in the eastern part of the profile. In order to solve the equivalence problem, seismic refraction work was carried out at some selected places; that yielded additional information on depths to bedrock. These seismic data made possible a unique solution of the electrical sounding curves, from which it could be concluded that all groundwater in the area is saline. Subsequent test drilling confirmed these findings. A regional relative Bouguer anomaly map provided a picture of the general geologic structures and made possible rough estimates of depths to bedrock. In areas where the basement rocks are relatively close to the surface, as is the case with the profile presented, the gravity anomalies cannot be correlated with bedrock relief, because the effect is strongly influenced by lateral density variations within the bedrock itself. This is an example of a case where only an integrated application of several geophysical exploration methods can provide the desired hydrogeologic information in an acceptable balance between reliability and cost.

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