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A method and apparatus for determining the resistivity of a formation through which a cased well passes

A technology of resistivity and casing, which is applied in the direction of electrical/magnetic detection for well logging records, and can solve the problems of complicated length and increase of measuring devices

Inactive Publication Date: 2004-09-29
SCHLUMBERGER TECH LTD BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

These proposals all suffer from the disadvantage of complicating the measuring device and in particular increasing its length

Method used

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  • A method and apparatus for determining the resistivity of a formation through which a cased well passes
  • A method and apparatus for determining the resistivity of a formation through which a cased well passes
  • A method and apparatus for determining the resistivity of a formation through which a cased well passes

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Embodiment Construction

[0019] The principle of measuring resistivity in a cased well is to cause a current flowing along the casing with a distant backflow, so that the current can leak to the formation through which the oil well passes to estimate the leakage current: at any point down the oil well At a given location, the higher the conductivity of the formation surrounding the well, the greater the leakage current. This can be expressed mathematically as a function of the ratio of the formation resistivity Rt to the casing resistivity Rc at any given location by the exponentially decreasing relationship of the current flowing through the casing, with a certain rate of decline .

[0020] The diagram in Figure 1 shows a section of a well 10, having an axis XX' and equipped with a metal casing 11. The desired position (or depth) to which a determination is to be made is referenced to the symbol b . Examine the stretch in position b A length of casing on both sides (a, c). If the current flows t...

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Abstract

The invention relates to a method of surveying the resistivity of a geological formation through which a borehole provided with metal casing passes, in which method a leakage current is caused to leak into said formation outside the casing, and said leakage current is determined on a casing section at a certain level, the leakage current being indicative of the resistivity of the formation. According to a characteristic of the invention, the resistivity is determined on the basis of the leakage current by applying a factor that depends on the distance z between said level and the surface.

Description

technical field [0001] This invention relates to the determination of the resistivity of formations through which a metal-cased well passes. Background technique [0002] The importance of resistivity measurements to petroleum exploration is well known. It is known that the resistivity of a formation depends primarily on the fluids it contains. A formation containing conductive brine has a much lower resistivity than a hydrocarbon-laden formation, so resistivity measurements are irreplaceable for locating hydrocarbon deposits. Resistivity logging has been widely practiced for many years, especially with the help of devices with some electrodes, but the various techniques available have the field of applicability limited to uncased oil wells, or as they are called in the oil industry terminology. Call it "naked eyes". If there is a metal casing in the oil well, the resistivity of the casing is small compared with the general values ​​of various for...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01V3/24
CPCG01V3/24
Inventor 玛丽-特里西·古诺特
Owner SCHLUMBERGER TECH LTD BV
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