Abstract:
A system and method are provided for drilling a wellbore. The wellbore is formed with a drilling tool that cuts through a formation. A pumping system removes cuttings from the drilling tool and also transports the cuttings along at least a portion of the wellbore formed behind the drilling tool.

Description:
BACKGROUND 
       [0001]    In a variety of subterranean environments, reservoirs hold desirable production fluids, such as petroleum. Wellbores often are drilled into the subterranean environments to facilitate production of the desired fluid. However, wellbores also can be drilled for a variety of other applications related to the fluid production. Such applications include, for example, facilitation of fluid production, fluid injection, sensor placement or other production related functions. The drilling can be oriented in, for example, vertical or deviated, e.g. lateral, directions with the aid of an appropriate drilling tool. 
         [0002]    When drilling, cuttings are produced by the action of the drilling tool excavating the borehole. Those cuttings have a larger volume than the original rock mass and therefore need to be removed for excavation of the wellbore. In the conventional drilling of vertical wellbores with drilling equipment deployed on tubing, the cuttings can be removed from the wellbore by circulating drilling mud to transport the cuttings along the wellbore. However, conventional cuttings removal techniques do not work well with, for example, wireline deployed cutting tools, even if a fluid conduit is deployed with the wireline. With wireline deployed systems, the power supply available is limited and there is only a single fluid filled wellbore region behind the drilling tool, thus rendering difficult the circulation of drilling fluid to remove cuttings. 
       SUMMARY 
       [0003]    In general, the present invention provides a system and methodology for drilling wellbores. A drilling tool is deployed downhole to cut through formation material in forming a desired wellbore or wellbores. A pumping system circulates fluid to remove cuttings from the drilling tool and to transport the cuttings away from the drilling tool along the wellbore being formed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0005]      FIG. 1  is an elevation view of a drilling system deployed in a wellbore, according to an embodiment of the present invention; 
           [0006]      FIG. 2  is an elevation view of an embodiment of a bottom hole assembly that can be used with the system illustrated in  FIG. 1 ; 
           [0007]      FIG. 3  is an alternate embodiment of the drilling system illustrated in  FIG. 1 ; and 
           [0008]      FIG. 4  is a schematic illustration of an embodiment of a drilling tool that can be used with the system illustrated in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0010]    The present invention generally relates to a system and method for drilling wellbores used, for example, in the production of desired fluids, e.g. petroleum. The system and method may be used with a variety of downhole drilling tools and equipment. Furthermore, the system and method may be used to form a variety of wellbores in numerous environments and applications, such as wireline services, through-tubing drilling, low-cost reentry drilling, sensor placement, fluid production, fluid injection optimization and other applications. However, the devices and methods of the present invention are not limited to the specific applications that are described herein. 
         [0011]    Referring generally to  FIG. 1 , a system  20  is illustrated according to an embodiment of the present invention. The system  20  is deployed in a wellbore  22  that has been cut into a formation  24 . In this embodiment, wellbore  22  comprises a main wellbore  26  and a deviated or lateral wellbore  28 . Lateral wellbore  28  extends from main wellbore  26  and provides a passageway to and from main wellbore  26 . As illustrated, main wellbore  26  is generally vertical and lateral wellbore  28  is generally horizontal, however the orientations of the wellbores with respect to each other and with respect to vertical or horizontal orientations may differ from one application to another. For example, lateral wellbore  28  is not necessarily horizontal but may extend at a declined or inclined orientation. 
         [0012]    In the embodiment illustrated, system  20  comprises a pumping system  30  that delivers separate, unique fluid flows to a drilling tool  32  and at least a portion of wellbore  22 , respectively. The unique fluid flows clear cuttings from drilling tool  32  and transport cuttings along the wellbore to a location where the cuttings do not interfere with the drilling operation or subsequent uses of the wellbore. In the example illustrated, a first-fluid flow clears cuttings from drilling tool  32  and moves them to lateral wellbore  28 . A second fluid flow then transports the cuttings along lateral wellbore  28  and deposits them in a downwardly extending section  34  of main wellbore  26 . 
         [0013]    In this embodiment, the first fluid flow is directed to drilling tool  32  at a higher pressure, lower flow rate relative to the second flow. The higher pressure enables the fluid to clear cuttings from drilling tool  32 . The second fluid flow is relatively lower pressure but has a greater flow rate to provide suitable transport of cuttings along lateral wellbore  28 . 
         [0014]    Referring again to the embodiment of  FIG. 1 , the illustrated pumping system  30  comprises two separate pumps, a first pump  36  to provide the first fluid flow to drilling tool  32  and a second pump  38  to provide the second fluid flow. By way of example, second pump  38  is located in main wellbore  26 , and first pump  36  is located in lateral wellbore  28 . However, the pumps may be positioned in a variety of locations depending on the drilling application, e.g., second pump  38  can be located outside main wellbore  26  in, for example, lateral wellbore  28 . By way of further example, first pump  36  and drilling tool  32  may be combined in a bottom hole assembly  40 . 
         [0015]    Although system  20  may utilize several components arranged in a variety of configurations, the illustrated embodiment provides one example. Specifically, second pump  38  is positioned in main wellbore  26  and coupled to a rear tractor  42  by a fluid conduit  44 . Rear tractor  42  is coupled to bottom hole assembly  40  by a transition pipe  46 . Second pump  38  draws fluid from main wellbore  26  and pumps the fluid through fluid conduit  44 , through rear tractor  42 , through transition pipe  46  and typically through at least a portion of bottom hole assembly  40 . As will be explained more fully below, the fluid is then expelled outwardly into the lateral wellbore surrounding bottom hole assembly  40 . The expelled fluid flows back along lateral wellbore  28  in sufficient volume to transport the cuttings along lateral wellbore  28  to a collection point, such as downwardly extending section  34 . 
         [0016]    As illustrated, drilling tool  32  and overall system  20  are deployed on a wireline  48 . Power may be supplied to system  20  through wireline  48 . However, the power supplied through a wireline often is limited to less than 10 kilowatts. Thus, the drilling system components, such as drilling tool  32 , pump  36  and pump  38  are designed to operate collectively within the power limitations. One example of a suitable wireline  48  is a quad cable that handles approximately nine kilowatts. In many system designs, the use of separate pumps for clearing cuttings from drilling tool  32  and for transporting cuttings along lateral wellbore  28  can make relatively efficient use of available power. 
         [0017]    A variety of bottom hole assemblies can be used in the illustrated system depending on the specific application, environment and design parameters. An embodiment of bottom hole assembly  40  is illustrated in  FIG. 2 . In this example, bottom hole assembly  40  comprises drilling tool  32  having a drilling motor  50 , a bearing housing  52  and a drilling bit  54 . The bottom hole assembly  40  also comprises first pump  36  which can be, for example, a progressing cavity pump, a centrifugal pump or a mixed flow pump. Between pump  36  and drilling tool  32 , bottom hole assembly  40  comprises at least one anchor, such as lower anchor  56  and upper anchor  58 . Lower anchor  56  and upper anchor  58  may be separated by a WOB piston  60 . Additionally, the assembly may comprise an orientor  62  for orienting the drilling via drilling bit  54 . An electronics chassis  64  may be located generally adjacent pump  36  and is designed to control the various electronic inputs to components of bottom hole assembly  40 . 
         [0018]    In an alternate embodiment, illustrated in  FIG. 3 , second pump  38 , e.g. a progressing cavity pump, is included in bottom hole assembly  40 . This type of configuration also can be designed to reverse circulate the cuttings such that the transport fluid is drawn down an annulus of the wellbore and then pumped back, along with the cuttings, through the central tubing to main wellbore  26 . Thus, various pumps and pumping systems can be used in unique selected locations within the wellbore. 
         [0019]    Regardless of the specific configuration of the pumping system  30 , the use of separate fluid flows to clean cutting bit  54  of drilling tool  32  and to transport cuttings along the wellbore provides a more efficient system amenable to deployment with a wireline. In the system illustrated, for example, first pump  36  is used to provide a fluid flow of relatively high pressure but low volume flow rate for efficient cleaning of drilling bit  54 . However, second pump  38  provides a second fluid flow at a higher volume flow rate but at a lower pressure, relative to first pump  36 . The second flow rate is sufficient to move cuttings along the wellbore, e.g. lateral wellbore  28 . The dual pumps provide greater power efficiency and an ability to remove cuttings with a wireline deployed system used for drilling lateral wellbores. The configuration enables the efficient cleaning of cuttings from the drilling bit  54  as well as the transport of those cuttings from the lateral wellbore  28 . 
         [0020]    To avoid problems in the transfer of cuttings] between the bottom hole assembly  40  and the main fluid transport flow through lateral wellbore  28 , a filter  66  may be used to prevent recirculation of cuttings, as illustrated in  FIG. 4 . In this embodiment, first pump  36  draws fluid through filter  66  and discharges the fluid into a passageway  68 . Passageway  68  conducts the fluid through drilling motor  50  and drilling bit  54  until the fluid is forced outwardly through one or more bit nozzles  70 . The outward flow of fluid through bit nozzles  70  washes cuttings away from drilling bit  54  and circulates the cuttings back through lateral wellbore  28  along the exterior of drilling motor  50  and pump  36 , as illustrated by arrows  72 . 
         [0021]    As the cuttings are cleared from drilling bit  54  and moved back along the lateral wellbore  28 , the cuttings are drawn into the main fluid transport flow. In this embodiment, the fluid transport flow, generated by second pump  38 , exits bottom hole assembly  40  through bypass ports  74 . The cuttings from drilling bit  54  are drawn into this transport stream, as represented by arrows  76 , and transported back along lateral wellbore  28 . As described previously, the cuttings can be transported to downwardly extending section  34  of main wellbore  26  or to some other collection location. 
         [0022]    Although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.