Patent Application
20060070734
This invention relates to a system and method for determining forces on a load-bearing tool in a wellbore in a downhole oil and gas recovery operation system.
An example of a load-bearing tool of the above type is a retrievable packer that is inserted in a wellbore in many oil field applications for the purpose of sealing against the flow of fluid and thus isolate one or more portions of the wellbore for the purposes of treating or producing the well. The packer is suspended from a workstring, or the like, in the wellbore, and includes one or more elastomer elements which are activated, or set, so that the elements are forced against an inner surface of the wellbore, or casing, and compressed to seal against the flow of fluid and therefore to permit isolation of certain zones in the well. The packer can be set by either setting down weight through the workstring which imparts a compressive load to the packer or by picking up on the workstring which imparts a tensile load to the packer. These setting loads or setting forces are referred to as a direct force.
After being set in the above manner, the packer can be subjected to various additional forces such as those related to workstring pressure and/or annulus pressure or by thermal expansion and contraction that occur when various fluids are pumped down the workstring. Since these forces may change the setting force on the packer and may otherwise adversely affect its operation, it is important that these additional forces be measured and their values either stored or transmitted to the surface in real time so as to permit remedial action.
To this end, strain gauges have been used to measure the direct force. However, strain gauges are sensitive to other conditions in the wellbore that can cause the additional forces on the packer. Therefore, the strain gauges measure a total force that is the sum of the direct force and the additional forces instead of measuring only the desired direct force.
In order to correct for this, various forms of mechanical and hydraulic devices have been used in an effort to compensate for the above additional forces caused by the other conditions in the wellbore. However, these compensation systems require additional components that can increase the length, complexity and cost of the system.
Therefore, what is needed is a system that compensates for the above additional forces while requiring few or no additional components.
Referring to
The workstring 14 extends from a rig 16 located above ground and extending over the wellbore 10. The rig 16 is conventional and, as such, includes support structure, a motor driven winch, or the like, and other associated equipment for lowering the tool 12, via the workstring 14, to a predetermined depth in the wellbore 10.
The upper portion of the wellbore 10 can be lined with a casing 20 which is cemented in the wellbore 10 by introducing cement in an annulus formed between the inner surface of the wellbore 10 and the outer surface of the casing 20, all in a conventional manner. A production tubing 22 having a diameter greater than that of the tool 12, but less than that of the casing 20, may also be installed in the wellbore 10 in a conventional manner and extends from the ground surface to a predetermined depth in the casing 20.
As viewed in
When actuated, or set, the tool 12 engages the corresponding inner wall portion of the casing 20 for the purpose of sealing against the passage of fluids across the tool 12.
A series of sensors 34 are mounted to the upper portion 12a of the tool 12 to sense a direct force. Each sensor 34 can be in the form of a metal foil strain gauge whose resistance varies in response to various forces applied thereto, which forces are largely in the form of tensile and compressive stresses on the tool 12 caused by setting the tool 12. Although only four sensors 34 are shown, it is understood that this number can vary.
As stated above, the sensors 34 are sensitive to other conditions in the wellbore 10 that can cause additional forces to act on the tool 12. Examples of these conditions include the temperature in the wellbore 10, pressure in the workstring 14, and/or differential pressure across the tool 12. To compensate for this a series of pressure gauges 36 and temperature gauges 38 are also mounted to the upper portion 12a of the tool 12. The gauges 36 and 38 can be in the form of piezo-resistive transducers, or any other conventional design, and, as such, are adapted to measure the pressure and temperature conditions in the wellbore 10 that affect the tool 12, and output corresponding signals. Although only two pressure gauges 36 and two temperature gauges 38 are shown mounted to the tool 12, it is understood that this number can vary. Pressure gauges 36 may for example be located in a cavity in the tool 12 and connected by ports to the interior of the workstring 14 and an annulus formed between the outer surface of the tool 12 and the inner wall portion of the casing 20.
A processor 40 is also mounted to the upper portion 12a of the tool 12, and, as shown in
In operation, the tool 12 is lowered to a predetermined depth in the wellbore 10 via the workstring 14, and the packer 12b is then set in a conventional manner. In performing this sealing function, the tool 12 is subjected to various forces, described below, in connection with the oil recovery process.
The sensors 34 sense a total force acting on the tool 12 and output corresponding signals to the processor 40. This total force includes the direct force on the tool 12 caused by setting the tool 12. However, the sensors 34 also sense the additional forces caused by other conditions in the wellbore 10 such as forces caused by thermal expansion and contraction that occur when various fluids are pumped down the workstring 14.
In order to determine these additional forces, the gauges 36 and 38 can measure the pressure in the workstring 14, the differential pressure across the tool 12, and/or the temperature in the wellbore 10 around the tool 12 and output corresponding signals to the processor 40.
The processor 40 includes a readable medium, or software, including instructions for execution by the processor 40, for calculating the direct force on the tool 12 from the total force and the additional forces in accordance with well known engineering principles. The additional force components are subtracted from the total force on the tool 12 measured by the sensors 34 to arrive at the direct force on the tool 12. The processor 40 then stores data based on these forces for downloading after the tool 12 is removed from the well, or the processor 40 can be designed to output a corresponding signal that is transmitted to the rig 16 in any conventional manner. This data is collected at the rig 16 and used to determine if the direct force caused by setting the tool 12 is such that remedial action is required.
It is understood that variations may be made in the foregoing without departing from the scope of the invention. Examples of some variations are as follows:
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
