Abstract:
An apparatus for use in gravel packing a well includes a tool body adapted to be lowered into the well, a screen coupled to the tool body, and a resilient member coupled to the screen. The apparatus is placed at a selected position in the well, and sand control media is disposed between the screen and the well while the resilient member is periodically excited to vibrate the screen.

Description:
This Appln claims the benefit of Provisional No. 60/093,959 filed Jul. 24, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates generally to downhole tools and methods for completing a well and, more particularly, to a downhole tool and method for placing a gravel pack in a well. 
     2. Background Art 
     In the petroleum industry, completion of a well drilled through subterranean formations generally involves lining the well with a casing and using a perforating gun to create perforation tunnels through the casing and the formation adjacent the casing. The perforation tunnels are usually created adjacent the formation at pay zones to allow reservoir fluids to flow from the formation into the well. During production of the reservoir fluids, sand may flow from the formation into the well if the formation is composed of unconsolidated sand. Typically, production of sand along with reservoir fluids is undesirable for many reasons, some of which include clogging of surface equipment, erosion of the tubing strings and wellhead, and bridging of the well such that further production of reservoir fluids is prevented. 
     However, production of sand along with reservoir sands is not a new problem in the petroleum industry, and there has been a lot of research and development in the area of sand control during reservoir fluid production. One sand control technique that has been found to be successful and reliable is gravel pack completion. Gravel pack completion involves placing a screen in the well adjacent the perforation tunnels and filling an annular area between the casing and the screen, as well as the perforation tunnels, with well-sorted, coarse sand, called gravel pack. The gravel pack is highly porous and permeable and serves to filter formation sand from the reservoir fluids entering the well. The filtering performance of the gravel pack depends on the size and shape of the gravel pack sand and how well the gravel pack fills the annular area between the casing and the screen. If there are voids in the gravel pack, the formation sand can fill the voids and reduce the rate at which the reservoir fluids are produced, or the produced sand can erode the screen and cause the gravel pack to fail. 
     One method for efficiently placing gravel pack in the well and the perforation tunnels is circulating gravel packing. A gravel pack tool is lowered into the well on the end of a tubing string and gravel suspended in a carrier fluid is pumped down the bore of the tubing string and through a crossover tool into the annular area between the screen and the casing. The gravel is held in place by the screen while the carrier fluid flows through the screen and crossover tool into the casing annulus and back to the surface. Generally, the gravel pack tool is substantially larger than the tubing string and would typically require that any existing tubing string and other restrictions in the well be removed before the gravel pack tool is run into the well. However, retrieval of existing tubing in a well is a relatively expensive operation and may not be economically viable for marginally producing or nearly depleted wells. 
     Another method for placing gravel pack in the well and the perforation tunnel involves pumping a gravel slurry in a viscous carrier fluid through a tubing string. The carrier fluid is squeezed into the formation and placed across the perforated interval. Again, while the tubing string may be lowered through an existing tubing in the well, the cost of deploying the tubing string may be fairly expensive for marginally producing wells. Thus, it would be beneficial to have a tool that can efficiently place a gravel pack in a well and that can be lowered into the well through a tubing and other restrictions in the well. U.S. Pat. Nos. 5,033,549 and 5,115,860 to Champeaux et al. disclose a gravel pack tool that can be lowered through a tubing on the end of an electric wireline. The gravel pack tool features radially extending members that collapse while the gravel pack tool is lowered through the tubing and extends when the gravel pack is placed below the tubing. Gravel is disposed in the well annulus using a dump bailer. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is an apparatus for use in gravel packing a well which comprises a tool body adapted to be lowered into the well and a screen coupled to the tool body. A resilient member is coupled to the screen to vibrate the screen in response to an excitation force. 
     Another aspect of the invention is a method for gravel packing a well which comprises placing a screen at a selected position in the well, disposing sand control media in an annulus between the screen and the well, and periodically vibrating the screen to allow for even filling of the annulus. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a downhole tool suspended in a well. 
     FIG. 2A is a cross-sectional view of the oscillating assembly referenced in FIG.  1 . 
     FIG. 2B is a cross-sectional view of the lower anchor shown in FIG. 2A in a deployed position. 
     FIG. 3A is a cross-sectional view of the latching head assembly shown in FIG. 1 in a running-in position. 
     FIG. 3B is a cross-sectional view of the latching head assembly shown in FIG. 3A in a deployed position. 
     FIG. 3C is a cross-sectional view of the latching head assembly attached to the vent pipe shown in FIG.  1 . 
     FIG. 4A shows a dump bailer attached to the latching head assembly shown in FIG.  3 A. 
     FIG. 4B shows the dump bailer actuator shown in FIG. 4A released from the latching head assembly. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings wherein like characters are used for like parts throughout the several views, FIG. 1 shows a downhole tool  100  suspended in a well  102 . A casing  104  extends along the length of the well  102 . The downhole tool  100  is concentrically received in the well  102  such that an annular area  106  is defined between the casing  104  and the tool  100 . The casing  104  includes perforations  108  which permit formation fluids from the formation adjacent the casing  104  to flow into the well  102 . The portion of the annular area  106  adjacent the perforations  108  is isolated at the bottom by a plug  110  and cement section  112 . The annular area above the cement section  112  is filled with a gravel pack  114 . The gravel pack  114  may be composed of any uniform, graded, commercial silica sand. The gravel pack  114  may also be composed of appropriately sized spherical ceramic beads. A cement cap  116  above the gravel pack  114  prevents the gravel pack  114  from loosening. 
     The tool  100  includes a flow segment  118 , a screen  120 , and an oscillating assembly  200 . The flow segment  118  includes a section of blank pipe  122 , a vent pipe  124 , and a latching head assembly  300 . The latching head assembly  300  includes an upper centralizer  302  which centers the tool  100  within the well and helps locate the top of the tool. The latching head assembly  300  also includes a latching head  304  which allows for easy retrieval of the tool and for latching onto the tool to operate the oscillating assembly  200 . The oscillating assembly  200  may be operated to oscillate the screen  120  to allow for efficient packing of gravel in the annular area between the casing and the screen. The lower end of the blank pipe  122  includes a threaded collar which mates with a similarly threaded collar on the upper end of the screen  120 . The blank pipe  122  provides a reservoir for extra gravel above the screen  120 . 
     Formation fluid flowing through the gravel pack  114  enters the screen  120  and flows upward into the vent pipe  124 , where it exits into the annular area above the cement cap  116 . The fluid in the annular area above the cement cap  116  may be returned to the surface through a tubing string (not shown). The screen  120  may be a wire-wrapped screen or other type of screen. There are many types of wire-wrapped screens, including ribbed, all-welded, groove, and wrapped-on-pipe. Typically, the all-welded screen is stronger and more corrosion-resistant and will not unravel if the wire is eroded or broken. The diameter of the screen  120  should be as large as possible and yet leave room for a gravel pack and be able to enter restricted diameter areas, such as tubing and valves, in the well. The screen size should be such that any formation sand entrained in the formation fluid does not get into the screen. The gravel size should be selected to restrict the movement of fine formation sand and, at the same time, allow production of formation fluids at economical rates. 
     Referring to FIGS. 2A and 2B, the oscillating assembly  200  includes an oscillating housing  202  and a mandrel  204 . The mandrel  204  is secured to an anchor assembly  206  that is adapted to engage the casing  104  upon landing on the cement section  112  (shown in FIG.  1 ). The anchor assembly  206  includes a fishing neck  208  that is secured to the lower end of the mandrel  204  by a shear pin  205 . A rod  210  extends from the fishing neck  208  through an anchor  212 . The anchor  212  is supported on an upper annular body  214 . Extending through the annular body  214  is an annular piston  216 . The upper end of the annular piston  216  is attached to the rod  210 . A mandrel  218  disposed within the annular piston  216  has one end attached to a bull nose  220 . The bull nose  220  is secured to the annular piston  216  by a shear pin  222 . 
     The bull nose  220  extends through a lower annular body  224 . An annular plate  226  is disposed about the annular piston  216 . The annular plate  226  is slidable along the length of the annular piston  216 . The annular plate  226  is coupled to the lower annular body  222  by a spring  228 . In the compressed state of the spring, collapsible collets  230  on the annular piston  216  restrict upward movement of the annular plate  226 . When the tool  100  lands on the cement section  112  with sufficient force to shear the shear pin  222 , the bull nose  220  retracts into the lower annular body  222  and pushes the mandrel  218  and rod  210  upwardly. This movement creates a gap between the annular plate  226  and the collets  230 , allowing the spring  228  to be released. The force of the spring  228  pushes the annular plate  226  over the collets and against the upper annular body  214  to deploy the anchor  212 . 
     The oscillating housing  202  includes a chamber  232  which houses a resilient member, for example, spring  234 . At the lower end of the spring  234  is a plate  236  which is attached to the mandrel  204 . The oscillating housing  202  may be moved up and down the mandrel  204  by compressing and extending the spring  234 . The axial axis of the mandrel  204  is generally aligned with the axial axis of the well  102  (shown in FIG. 1) so that the oscillating housing  202  moves along the axial axis of the well  102 . As the oscillating housing  202  moves, the screen  120  mounted on top of the oscillating housing  202  also moves. This allows for even filling of the annular area between the casing  104  and the screen  120  during gravel packing. A key  238  and slot  240  is provided on the mandrel  204  to allow the oscillating housing  202  and other components above the oscillating housing  202  to turn as the oscillating housing  202  moves relative to the mandrel  204 . The shear pin  205  holding the mandrel  204  to the fishing neck  208  is not sheared when the oscillating housing  202  moves relative to the mandrel  204  or when the anchor  212  is deployed. However, the shear pin  205  may be sheared at a later time to permit the tool  100  to be retrieved from the well. 
     Referring to FIGS. 3A and 3B, the latching head assembly  300  includes a body  306 . The latching head  304 , previously illustrated in FIG. 1, is attached to the body  306 . The upper end of the body  306  includes a threaded collar  308  which allows another threaded tool section to be attached to the body  306 . The upper centralizer  302  has one end connected to the threaded collar  308  and a second end connected to a washer  310  that is disposed about the body  306 . A spring  312  has one end connected to the washer  310  and another end connected to the lower end  314  of the body  306 . The spring  312  is held in a compressed state by locking pins  316 . The locking pins  316  are located in grooves in the body  306 . Extending through the center of the body  306  is a deployment rod  318 . The deployment rod  318  is movable within the body  306  by a releasing tool (not shown). 
     When the deployment rod  318  is used to run the tool  100  into the well, the locking pins  316  have one end abutting against the washer  310  and another end abutting against the deployment rod  318 . The locking pins  316  move inwardly into the body  306  to allow the spring  312  to extend when the deployment rod  318  is released from the body  306 . As the spring  312  extends, the upper centralizer  302  extends and centers the tool  100  within the well. The anchor of the upper centralizer  302  is such that when the tool  100  is retrieved, the upper centralizer  302  collapses back to allow the tool to be pulled through restricted diameter area. 
     Referring to FIG. 3C, the latching head assembly  300  includes a mechanical jar  320  which is fixed to the lower end  314  of the body  306 . The mechanical jar  320  extends into the vent pipe  124  and is held in place in the vent pipe  124  by a shear pin  322 . The shear pin  322  is sheared when the tool is dropped on the cement section  112 . When the shear pin  322  is sheared, the lower end  314  of the body  306  sits on a shoulder  324  at the upper end of the vent pipe  124 . The mechanical jar  320  is like a hammer and may be stroked to vibrate the spring  234  in the oscillating housing  202  such that the oscillating housing  202  moves up and down the mandrel  204 . As the oscillating housing  202  moves up and down, the screen  120  also moves up and down. The mechanical jar  320  may be stroked by latching onto the latching head  304 , raising the latching assembly  300  to a sufficient height, and then subsequently dropping the latching assembly  300 . When the latching assembly  300  is dropped, the mechanical jar  320  provides the energy required to vibrate the spring  234 . At the end of the mechanical jar  320  is a retaining nut  326  which ensures that the latching head assembly remains coupled to the vent pipe  124 . 
     Referring to FIGS. 4A and 4B, a release tool, for example, a dump bailer actuator  400 , is shown attached to the latching head assembly  300 . The dump bailer actuator  400  includes an extension sleeve  402  which is mounted on a tapered skirt  404  and a grapple  406  that latches onto the latching head  304 . At the upper end of the grapple  406  is a plate  408 . A deployment rod  410  extends from the plate  408  into the latching head assembly  300 . The deployment rod  410  and lock pins  316  prevent the spring  312  from extending to open the upper centralizer  302  before the dump bailer actuator  400  releases the latching head assembly  300 . A weight bar extension  412  is mounted on the plate  408 . The bar extension  412  is connected to a body  414  by a collet  416 . A spring  418  extends between the body  414  and the plate  408 . The spring  418  is in a compressed state until the dump bailer actuator  400  is actuated to release the latching head assembly  300 . 
     The dump bailer actuator  400  is operated by moving the extension sleeve  402  and the tapered skirt  404  upwardly such that the grapple  406  slides into the tapered skirt  404 . When the grapple  406  slides into the tapered skirt, the spring  418  is extended and the bar extension  412  is separated from the body  414 . The grapple  406  releases the latching head  304  when it engages the tapered skirt  404 , thus allowing the dump bailer actuator  400  to be separated from the latching head assembly  300 . As the dump bailer actuator  400  is pulled from the latching head assembly, the deployment rod  410  is pulled out of the latching head assembly  300  and the locking pins  316  move inwardly to allow the spring  312  to open the centralizer  302 . 
     In operation, when it is desired to gravel pack a new zone, the plug  110  and the cement  112  are set below the new zone. Then a perforating gun is lowered to the new zone to make perforations in the casing  104  and the formation adjacent the casing. When the perforations are made, a release tool, for example, the dump bailer actuator  400 , is attached to the tool  100  and the release tool and the tool  100  are lowered to the new zone on the end of a wireline, a slickline or other suitable conveyance device. The release tool is then operated to release the tool  100  such that the tool  100  lands on the cement  112  with sufficient force to release the anchor  212 . The released anchor  212  tightly engages the casing  104  and holds the tool  100  in place in the well. The upper centralizer  302  opens when the release tool is detached from the tool  100  and centers the tool  100  within the well. At the same time that the tool  100  is anchored and the upper centralizer  302  is opened, the mechanical jar  320  is sheared from the vent pipe  124 . This makes it possible to latch on the latching head assembly  300  and stroke the mechanical jar  320 . The latching head assembly  300  can also be used to retrieve the tool  100 . 
     Gravel may be dumped between casing  104  and the screen  120  by a dump bailer. The dump bailer may be a bailer with a frangible bottom that can be opened with an explosive charge. The dump bailer may also be a bailer that can be latched onto the latching head assembly  300  and that has a dump port that can be mechanically opened to dump gravel into the well. The dump bailer is small enough that it can fit through restricted diameters, such as a tubing string, in the well. When the gravel is dumped, the oscillating assembly  200  can be operated to oscillate the screen  120  to ensure that voids in the gravel pack are filled with gravel. More gravel can be dumped into the well until the gravel pack level rises above the upper end of the screen  120 . Then the cement cap  116  can be put in place to keep the gravel from loosening. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous variations therefrom without departing from the spirit and scope of the invention. For example, the latching head assembly  300  is shown as having one latching head  304 , but additional fishing necks can be added to the latching head to allow different types of tools to be latched onto the latching head assembly  300 . The latching head and fishing neck may be provided with magnetic markers which will allow a magnetic sensor, for example, a collar locator, to locate them downhole. Additional centralizers may be added to the tool  100  below the flow segment  118  to further centralize the tool  100  within the well.