Insulating or modified conductivity casing in casing string

Abstract

A casing string in a wellbore has conductive tubulars and modified conductivity (MC) or non-conductive tubulars joined to one another. A MC / non-conductive tubular may be disposed between two conductive tubulars. If there are at least two MC / non-conductive tubulars and at least three conductive tubulars, two of the MC / non-conductive tubulars may be alternately disposed between three of the conductive tubulars. The MC / non-conductive tubulars may be formed from materials such as stainless steel, fiber-reinforced thermal sets, and thermal plastics. One such thermal plastic is polyetheretherketone (PEEK) and it may be glass-reinforced. The conductive tubulars, if electrically isolated, may be used as electrodes to transmit or receive electromagnetic signals. The casing string may used for borehole to surface applications, surface to borehole applications, borehole to borehole applications, or single well applications. The casing string may also have downhole sensors, uphole sensors, and surface sensors. Those sensors may be transmitters or receivers.

Description

CROSS-REFERENCE TO OTHER APPLICATIONS[0001]This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 61 / 348,517, filed on May 26, 2010.BACKGROUND[0002]1. Technical Field[0003]The present disclosure relates generally to the logging of subsurface formations surrounding a wellbore using a downhole logging tool, and particularly to determining electrical properties of the formation behind a cased wellbore.[0004]2. Background Art[0005]Logging tools have long been used in wellbores to make, for example, formation evaluation measurements to infer properties of the formations surrounding the borehole and the fluids in the formations. Common logging tools include electromagnetic tools, nuclear tools, and nuclear magnetic resonance (NMR) tools, though various other tool types are also used.[0006]Early logging tools were run into a wellbore on a wireline cable, after the wellbore had been drilled. Modern versions of such wireline tools are still used extensiv...

AI Technical Summary

Benefits of technology

[0008]A casing string in a wellbore has conductive tubulars and modified conductivity (MC) or non-conductive tubulars joined to one another. A MC/non-conductive tubular may be disposed between two conductive tubulars. If there are at least two MC/non-conductive tubulars and at least three conductive tubulars, two of the MC/non-conductive tubulars may be alternately disposed between three of the conductive tubulars. The MC/non-conductive tubulars may be formed from materials such as stainless steel, fiber-reinforced thermal sets

Problems solved by technology

Measurements are typically performed in an uncased portion of the wellbore because conventional conductive casing tends to limit the electromagnetic signal that can pass between the interior and exterior of a cased wellbore.

This is not necessarily an issue when a well is being drilled since measurements can be made prior to setting the casing, but presents a challenge should one wish to re-enter an existing cased wellbore to make updated measurements.

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