Patent Application
20050167094
This disclosure relates to a system and method for determining load transmitted to a downhole tool in oil and gas recovery operations.
Many downhole tools are subjected to loads during oil and gas recovery operations. For example, packers are used to seal against the flow of fluid to isolate one or more sections, or formations, of a wellbore and to assist in displacing various fluids into the formation and/or retrieving hydrocarbons from the formation. The packers are suspended in the wellbore, or in a casing in the wellbore, from a work string, or the like, consisting of a plurality of connected tubulars or coiled tubing. Each packer includes one or more elastomer elements, also known as packer elements, which are activated, or set, so that they are forced against the inner surface of the wellbore, or casing, and compressed to seal against the flow of fluid and therefore to isolate certain zones in the well. Also, mechanical slips are located above and/or below the packer elements and, when activated, are adapted to extend outwardly to engage, or grip, the casing or wellbore.
The packer is usually set at the desired depth in the wellbore by picking up on the work string at the surface, rotating the work string, and then lowering the work string until an indicator at the surface indicates that some of the slips, usually the ones located below the packer elements, have extended outwardly to engage the casing or wellbore. As additional work string weight is set down on the engaged slips, the packer elements expand and seal off against the casing or wellbore. Alternately, the packer can be set by establishing a hydraulic pressure into a setting mechanism by the work string. The setting mechanism then extends, sets the packer, and expands all slips to engage the casing or wellbore.
Usually, the setting and sealing is accomplished due to the fact that the packer elements are kept sealed against the casing or wellbore by the weight, or load, of the work string acting against the slips. It can be appreciated that it would be advantageous to be able to monitor, evaluate, and, if necessary, vary, the load transmitted to the packer and other downhole packers. Although a weight indicator has been provided at the surface for this purpose, it is often difficult to determine exactly how much load is being transmitted due, for example, to buckling and corkscrewing of the work string, irregular wellbore diameters, etc.
Therefore, what is needed is a system and method for sensing and monitoring the load transmitted to a downhole packer in the above manner so that the load can be evaluated and, if necessary, adjusted.
Referring to
The work string 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, draw works, a motor driven winch, and/or other associated equipment for receiving and supporting the work string 14 and the tool 12 and lowering the packer 12 to the predetermined depth in the wellbore 10.
The wellbore 10 can be lined with a casing 18 which is cemented in the wellbore 10 by introducing cement in an annulus formed between an inner surface of the wellbore 10 and an outer surface of the casing 18, all in a conventional manner.
The tool 12 is shown in detail in
Packer element 22 comprises two axially-spaced annular packer elements 22a and 22b extending around the mandrel section 20a and between a shoulder formed on the mandrel section 20a and the corresponding end of the mandrel section 22b. The packer elements 22a and 22b are adapted to be set, or activated, in the manner discussed above which causes them to extend radially outwardly to the position shown in
The packer element 22b is spaced axially from the packer element 22a, and a spacer ring 24 extends around the mandrel section 20a and between the packer elements 22a and 22b. A shoe 26a extends around the mandrel section 20a just above an upper end of the packer element 22a, and a shoe 26b extends around the mandrel section 20a just below a lower end of the packer element 22b.
A plurality of mechanical slip elements 28, two of which are shown in
Three axially-spaced sensors 30a, 30b, and 30c are located on the mandrel 20, and a sensor 30d is located on each slip element 28. Three additional sensors 30e, 30f, and 30g are located on the spacer ring 24, the shoe 26a, and the shoe 26b, respectively.
Before the sensors 30a-30g are applied to the tool 12 in the above locations, they are embedded in a non-metallic material and the material is applied to the tool. For example, the sensors 30a-30g can be embedded in a laminated structure including multiple sheets of material that are laminated together. Each sheet is formed of a composite material including a matrix material, such as a polymer and a braid impregnated in the matrix material. The braid could be in the form of a single strand or multiple strands woven in a fabric form. The sensors 30a-30g, along with the necessary electrical conductors, are placed either in the matrix material or within the braided strands of the braid. The sheets are adhered together with an adhesive, a plastic material, or the like, to form the laminated structure. Alternately the sensors 30a-30g could be located between adjacent sheets in the above laminated structure.
The laminated structure thus formed, including the sensors 30a-30g, can be attached to an appropriate surface of the mandrel 20, the slip elements 28, the spacer ring 24, and/or the shoes 26a and 26b in any conventional manner, such as by adhesive, or the like, or they can be placed loosely against an appropriate structure.
The above-mentioned electrical conductors associated with the sensors 30a-30g are connected to appropriate apparatus for transmitting the output signals from the sensors 30a-30g to the ground surface. For example, each sensor 30a-30g can be hardwired to central storage/calibration electronics (not shown) at the ground surface using electrical conductors or fiber optics. Alternately, data from the sensors 30a-30g can be transmitted to central storage/calibration electronics at the ground surface via high-frequency, radio frequency, electromagnets, or acoustic telemetry. Also, it is understood that each sensor 30a-30g can be set up to store data independently from the other sensors and the stored data can be accessed when the tool 12 is returned to the ground surface.
Alternately, one or more of the mandrel 20, the spacer ring 24, and/or the shoes 26a and 26b can be fabricated from the above laminated structure including the sensors 30a-30g and the appropriate electrical conductors. A technique of incorporating sensors in structure not related to downhole tools is disclosed in a paper entitled “Integrated Sensing in Structural Composites” presented by A. Starr, S. Nemat-Nasser, D. R. Smith, and T. A. Plaisted at the 4th Annual International Workshop for Structural Health Monitoring at Stanford University on Sep. 15, 2003, the disclosure of which is incorporated herein by reference in its entirety.
In each of the above cases, all loads transmitted to the mandrel 20, the slip elements 28, the spacer ring 24, and/or the shoes 26a and 26b are sensed by the sensors 30a-30g.
The sensors 30a-30g can be in the form of conventional strain gauges which are adapted to sense the stress in the mandrel 20, the packer element 22, the slip elements 28, the spacer ring 24, and the shoes 26a and 26b and generate a corresponding output signal. An example of this type of sensor is marketed under the name Weight-on-Bit (WOB)/Torque Sensor, by AnTech in Exeter, England and is disclosed on Antech's Internet website at the following URL address: http://www.antech.co.uk/index.html, and the disclosure is incorporated herein by reference in its entirety.
The sensors 30a-30g can be connected in a conventional Wheatstone bridge with the measurements of strain (elongation) by the sensors 30a-30g being indicative of stress level. As a result, the load on the mandrel 20, the packer element 22, the slip elements 28, the spacer ring 24, and the shoes 26a and 22b can be calculated as follows:
L=S(A)
where:
It is understood that, additional electronics, such as a power supply, a data storage mechanism, and the like, can be located anywhere on the tool 12 and can be associated with the sensors 30a-30g to enable and assist the sensors 30a-30g to function in the above manner. Since these electronics are conventional they are not shown nor will they be described in detail.
The sensors 30a-30g can be set up to store data independently from the other sensors, or can be “hardwired” to central storage/calibration electronics (not shown) using electrical conductors (wire) or fiber optics, or can be connected locally to central storage/calibration electronics via high-frequency, radio/frequency, electromagnetic, or acoustic telemetry.
The readings from all the sensors 30a-30g can be used individually or can be combined to form a “virtual” sensor anywhere on the tool 12. In other words, the readings from all or a portion of the sensors 30a-30g can be used to estimate the stress/strain, etc. at any point on the tool 12 including actual sensor locations. Even though one of the sensors 30a-30g may be present at a location of interest on the tool 12, the accuracy of the measurement may be improved by also using the other sensor measurements as well. Also, a calibration can be performed on the entire tool 12 under various loading conditions, in a manner so that it would not be necessary to precisely align or attach the sensors 30a-30g in a particular way, since the calibration would compensate for sensor misalignment, etc.
1. The number of sensors 30a-30g that are used on the tool 12 can be varied.
2. The sensors 30a-30g can be located anywhere on the mandrel 20, the slip elements 28, the spacer ring 24, and the shoes 26a and 26b, preferably in areas subjected to relatively high strain, and could also be located on one or more of the packer elements 22a and 22b.
3. The location of the sensors 30a-30g is not limited to the mandrel 20, the slip elements 28, the spacer ring 24, and the shoes 26a and 26b, but could be at any area(s) of the tool 12.
4. The sensors 30a-30g are not limited to strain gauges but rather can be in the form of any type of sensors that sense load.
5. The material in which the sensors 30a-30g are embedded can vary. For example the material can be an elastomer, ceramic, plastic, glass, foam, or wood with or without the above-mentioned braid integrated therein. Also, the material does not necessarily have to be in the form of sheets or laminated sheets.
6. Although the tool 12 is shown in a substantial vertical alignment in the wellbore 10, it is understood that the packer 12 and the wellbore 10 can extend at an angle to the vertical.
7. The present invention is not limited to sensing loads on packers but rather is applicable to any downhole tool.
8. The spatial references mentioned above, such as “upper”, “lower”, “under”, “over”, “between”, “outer”, “inner”, and “surrounding” are for the purpose of illustration only and do not limit the specific orientation or location of the components described above.
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.
