BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to measuring stresses, strains and changes in stress and strain in a subterranean wellbore.

2. Description of the Relevant Art

There are a variety of methods currently used for estimating the orientation and magnitude of the in-situ stress and changes in the stress around the wellbore. Current methods include, but are not limited to: (i) imaging borehole breakouts; (ii) shear wave anisotropy; (iii) downhole or surface tiltmeters; (iv) inelastic strain relaxation; (v) imaging natural and drilling induced fractures; (vi) downhole or surface microseismic measurements. Most of these methods have some key shortcomings, limitations, and challenges:1. Most of these methods do not have the ability to continuously measure and monitor changes in the in-situ stress over a period of time.2. Most of these methods are unable to monitor changes in the stress or stain field during a fracturing operation in a nearby well.3. None of the methods is able to accurately quantify the magnitude and orientation of the maximum and minimum horizontal stress.4. Most of these methods are very expensive to use and, therefore, not commonly applied.5. Many methods require specialized tools, procedures or models to use and interpret.

Some downhole strain sensors used in wells are composed of long fiber optic cables, strapped to or wound around the outside of the casing. Moreover, in order to protect the fiber optic cable the strain sensor is actually embedded in several layers of insulating materials (typically a steel tube filled with a gel). Accurately measuring strain through multiple layers of material is very difficult to achieve and the resulting uncertainty is problematic.

PCT Publication No. WO 96/231216 entitled “Borehole Strainmeter” discusses a generally longitudinal strain measurement device that measures change in length and are only suitable for vertical pipes. The devices described in WO 96/231216 are single point devices that appear to be both extremely delicate and sensitive.

It is desirable to have a device for measuring strain that measures the radial strain in a wellbore casing at different orientations or azimuths at different locations in a well. This sensor array is much more robust and is designed to be used in a linear array of either horizontal or vertical pipes.

SUMMARY OF THE INVENTION

In an embodiment, a device for measuring the axial or radial strain of a pipe includes: one or more elastically deformable members with different radial orientations in a wellbore, wherein each of the one or more elastically deformable members comprise an outer contact surface and an inner non-contact surface; and one or more sensors disposed on the inner non-contact surface of one or more of the elastically deformable members. The sensors, during use, provide data that can be used to determine changes in radial strain in the pipe at different azimuthal orientations. As used herein, an azimuthal orientation refers to a projected vector extending from an origin (typically a point at the center of the wellbore or pipe) to a point that is projected perpendicularly onto the surface of the pipe or wellbore. The angle between the projected vector and a reference vector on the reference plane is called the azimuth.

In an embodiment, a method of measuring strain in the pipe positioned in a wellbore includes positioning a device or a system, as described above, inside the pipe such that the elastically deformable members of the device contact the interior surface of the pipe.

In an embodiment, a method of measuring strain in an open hole of a wellbore includes positioning a device or a system, as described above, inside the open hole such that the elastically deformable members of the device contact the sidewalls of the open hole.

In an embodiment, a method of measuring strain in a cased wellbore includes positioning a device or a system, as described above, inside the open hole such that the elastically deformable members of the device contact the sidewalls of the open hole.

In an embodiment, a method includes measuring axial or radial strain at different azimuthal orientations in an open-hole wellbore or a cased and cemented wellbore.

In an embodiment, a method includes measuring the axial or radial strain at different azimuthal orientations in an open hole wellbore or a metal cased and cemented wellbore as a portion of the wellbore is pressurized with fluid.

In an embodiment, a method includes measuring axial or radial strain at different azimuthal orientations in an open-hole wellbore or a metal cased, cemented wellbore as the rock around the wellbore is hydraulically fractured from the same wellbore or from another wellbore.

In an embodiment, a method includes pressurizing or depressurizing the wellbore with any fluid and measuring the strain induced in the casing (or in an open wellbore) in response to this change in wellbore pressure.

