Surface to borehole electromagnetic surveying using metallic well casings as electrodes
AssigneeSchlumberger Technology Corporation
InventorsHong Zhang, Richard A. Rosthal
Life of this patent
Estimating the term…
Abstract
Methods and related systems are described for making measurements of an electromagnetic field in a subterranean formation that has been induced by a current loop. The current loop uses one or more steel wellbore casings as electrodes. Receiver arrays are positioned either at surface/seafloor, in the same, or in nearby wells. In the most general case, the receivers are tri-axial. A section of metallic casing in one well can be used as a current source and the electromagnetic field at surface can be measured using an array of EM receivers placed at a range of distances from the wellbore.
Claims37
A downhole tool system for making electromagnetic measurements of a subterranean formation comprising:
- a first downhole tool deployable in a metallic cased wellbore and adapted to make electrical contact with a wall of the metallic casing so as to establish a current loop that partially includes the metallic casing wall;
- and
- one or more receivers deployable and adapted so as to inductively detect a field in the formation that has been produced by the established current loop;
- wherein the first downhole tool comprises a first unit deployable and adapted to make electrical contact with the metallic casing wall at a first location and a second unit deployable and adapted to make electrical contact with the metallic casing wall at a second location, wherein the established current loop includes at least a portion of the casing wall between the first and second location;
- and
- wherein the first and second units are configured to be repositionable in relation to one another while the tool is deployed downhole to alter the distance between the first and second locations while the tool is deployed downhole.
A method for making electromagnetic measurements of a subterranean formation comprising:
- deploying a first tool in a first metallic cased wellbore;
- electrically contacting a wall of the casing of first wellbore using the first tool;
- establishing a current loop that partially includes a portion of the metallic casing wall of the first wellbore, wherein the current loop induces a field in the subterranean formation;
- deploying a second downhole tool in a second metallic cased wellbore;
- electrically contacting a wall of the casing of the second wellbore, wherein the established current loop includes the first tool, part of the metallic casing of the first wellbore, part of the subterranean formation, part of the metallic casing of the second wellbore, and the second tool;
- and
- inductively detecting the field using one or more receivers.
A downhole tool system for making electromagnetic measurements of a subterranean formation comprising:
- a first downhole tool deployable in a metallic cased wellbore and adapted to make electrical contact with a wall of the metallic casing so as to establish a current loop that partially includes the metallic casing wall;
- and
- one or more surface receivers deployable on an earth surface or sea floor and adapted so as to detect a field in the formation that has been produced by the established current loop;
- wherein the first downhole tool comprises a first unit deployable and adapted to make electrical contact with the metallic casing wall at a first location and a second unit deployable and adapted to make electrical contact with the metallic casing wall at a second location, wherein the established current loop includes at least a portion of the casing wall between the first and second location;
- and
- wherein the first and second units are configured to be repositionable in relation to one another while the tool is deployed downhole to alter the distance between the first and second locations while the tool is deployed downhole.
A method for making electromagnetic measurements of a subterranean formation comprising:
- deploying a first tool in a first metallic cased wellbore, wherein the first downhole tool comprises a first unit and a second unit;
- electrically contacting a wall of the casing of first wellbore using the first unit and the second unit, wherein the first unit electrically contacts the metallic casing wall at a first location and a second unit electrically contacts the metallic casing wall at a second location;
- establishing a current loop that partially includes a portion of the metallic casing wall of the first wellbore, wherein the current loop induces a field in the subterranean formation, wherein the established current loop includes at least a portion of the casing wall between the first and second location;
- deploying one or more surface receivers on an earth surface or on a sea floor;
- detecting the field using the one or more surface receivers;
- repositioning the first unit in relation to the second unit or the second unit in relation to the first unit, or both, to vary the first location or the second location or both the first location and the second location;
- and
- repeating the detection of the electrical field.
Dependencies are inferred from the claim text.