Abstract:
Disclosed embodiments include a surge relief system for a bottom hole assembly (BHA) and drill bit on an offshore drill string. One embodiment includes flow passages and external ports arranged to manage flow of wellbore fluids during sudden movements of the BHA and drill bit caused by waves. A first relief valve in the first flow passage is disposed to activate at a predetermined pressure to allow flow therethrough. Additional flow passages and pressure relief valves may be sequentially positioned along the length of the BHA/drill bit system to further assist in a managed bleed of pressurized fluid through the surge relief system. The sequential pressure relief valves may have activation pressures that sequentially increase or decrease.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure relates to an apparatus and method for accommodating surge and swab experienced at the bottomhole assembly (BHA) of a drill string during tripping procedures from a marine platform. More particularly, the disclosure provides for a surge relief system carried by the drill string adjacent the drill bit to minimize damage to the formation that could be experienced as a result of movement of the platform during tripping procedures. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Drilling for oil and gas off-shore is completed from one of two general types of drilling platforms, namely, platforms that are supported by the sea floor, such as fixed drilling rigs and jack-up drilling rigs, or platforms that float near or on the surface of the water, such as drill ships, spar, semi-submersibles and the like. Although drilling operations conducted from these types of drilling platforms are similar, at least one major difference exists: floating platforms move with the waves of the sea and wind, while fixed or jack-up drilling rigs remain fixed to the sea floor. 
         [0003]    The movement of drilling platforms caused by waves and wind presents a unique problem in drilling with these types of platforms. Most common among these problems is that of heave on the drill string during drilling, namely movement of the drill string up and down with the waves during drilling operations. In particular, as the floating rig moves up and down, the drill string extending below the rig will also move up and down and correspondingly, the drill bit at the end of the drill string will move as it is engaging the formation. For a drill bit to perform as efficiently as possible, the desired or optimum weight on the drill bit (“WOB”)—i.e., the downward force applied to the bit—must be kept as constant as possible. Heave, however, removes weight from the drill bit as the ship or rig rides to the crest of a wave, and puts weight back on the drill bit as the ship or rig rides down into the trough between waves. 
         [0004]    This fluctuation in the force applied on the drill bit severely hinders an operator&#39;s ability to drill the well bore. 
         [0005]    To account for this problem associated with heave, floating drilling platforms are equipped with heave compensation systems. The heave compensation systems are typically in the form of an active heave drawworks system or a system that is an integral part of the drilling derrick or mounted directly on an extension of the traveling block. Such systems are intended to protect against the effects of heave during drilling operations to ensure appropriate WOB is maintained. 
         [0006]    Heretofore, little, if any, attention has been focused to the effects of heave on a drillstring as it is tripped into and out of a wellbore. The drill string, and in particular, the bottom hole assembly and drill bit will experience upward and downward motion as it moved tripped in and out. This will cause the bit and BHA to act as a piston on the fluid in the wellbore, driving the wellbore fluid to create surge and swab effects on the surrounding formation. These effects can severely damage the formation by alternatively applying excess pressure to the formation by forcing wellbore fluids into the formation as the drill string is driven down into the wellbore by wave motion, in which case, wellbore fluids surge out into the formation, and forcibly drawing formation fluids out of the formation into the wellbore as the drill string is pulled up in the wellbore due to reduced wellbore pressure as the drill string is drawn up. Swabbing is generally considered harmful in wellbore operations, because it can lead to kicks and wellbore stability problems. 
         [0007]    Accordingly, what is needed is a system to minimize the effects of swab and surge caused by heave on a drillstring as it is tripped into and out of a wellbore. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a floating platform with a drill string that would be subject to surge and swab effects from heave. 
           [0009]      FIG. 2  illustrates a surge relief system in a drill string. 
           [0010]      FIG. 3  illustrates a surge relief system in a drill string having a mud motor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    The foregoing disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “uphole,” “downhole” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as being “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
         [0012]    With reference to  FIG. 1 , there is shown a floating drilling platform  10  generally floating at the surface  12  of a body of water  14 . A wellbore  16  extends into a formation  18  from the seabed  20  and includes wellbore fluid  22  disposed therein. A drill string  24  extends down from platform  10  and into wellbore  16 . The drill string  24  generally includes a bottom hole assembly (“BHA”)  26  and a drill bit  28 . In the illustration of  FIG. 1 , persons of ordinary skill in the art will understand that the drill string  24  is being illustrated during tripping of the drill string  24  either into or out of wellbore  16  since the drill bit  28  is not engaged with the formation  18 . 
         [0013]    With reference to  FIG. 2 , the BHA  26  and drill bit  28  are provided with a surge relief system  30 . The surge relief system  30  generally includes a plurality of flow passages  32  and pressure relief valves  34  disposed in BHA  26  in order to manage wellbore fluid  22  surge and swab effects resulting from heave of drill string  24  as platform  10  moves about at surface  12 . More specifically, BHA  26  includes an elongated tubular member  36  having a first end  38  and a second end  40  with an internal annulus  42  extending therebetween. First end  38  is attached to a pipe string  44  in a well-known manner so that an annulus  46  of pipe string  44  is in fluid communication with annulus  42  of BHA  26 . BHA  26  includes an exterior surface  48  that is generally exposed to the open wellbore  16  and wellbore fluid  22 . 
         [0014]    Drill bit  28  has a proximal end  48  and a distal end  50 . Drill bit  28  is also provided with an annulus  52  that extends at least partially through drill bit  28 . It will be appreciated that annulus  52  may be open to the wellbore  16  in any of a variety of known configurations, such as via jets (not shown) disposed in the body of drill bit  28  or other openings, such as opening  54 , so as to supply drilling mud to wellbore  16 . The embodiments described herein are not limited to a particular type of BHA assembly or drill bit or configuration of the two; rather, the valves  34  and passages  32  may be accordingly disposed in many different types of BHAs and drill bits disposed on a drill string. 
         [0015]    In any event, the surge relief system  30  includes a first flow passage  32   a  defined in drill bit  28 . First flow passage  32   a  has a first port  54  at the distal end  50  of drill bit  28 . In certain preferred embodiments, first port  54  is axially disposed so as to open towards the bottom of wellbore  16  when drill bit  28  is positioned therein. In certain preferred embodiments, first port  54  is the opening for annulus  52 . 
         [0016]    First flow passage  32   a  also has a second port  56 . Second port  56  is preferably positioned between the distal end  50  of drill bit  28  and the second end  40  of BHA  36 , although it should be understood that that first flow passage  32   a  may have any position or orientation so long as it permits pressure relief from flow through first port  54  in drill bit  28 . In certain preferred embodiments, second port  56  is disposed at proximal end  48  of drill bit  28 , while in other embodiments, second port  56  may be along the length of drill bit  28 . In yet other embodiments, first flow passage  32   a  may extend into BHA  26 , in which case, second port  56  may be positioned on the exterior  48  of tubular  36 . A first relief valve  34   a  is disposed in first passage  32   a  between the first and second ports  54 ,  56 , respectively. In certain preferred embodiments, valve  34   a  is adjacent second port  56 . 
         [0017]    While surge relief system  30  may simply utilize a single passage with a relief valve disposed therein, surge relief system  30  may further include a second flow passage  32   b . Although it may be defined in drill bit  28  in certain embodiments, preferably second flow passage  32   b  is disposed in tubular  36  between the first end  38  and second end  40 . Second flow passage  32   b  has a third port  58 . Third port  58  is preferably positioned between the first and second ends  38 ,  40 , respectively, of tubular  36 . In preferred embodiments, third port  58  is uphole from second port  56  and defined in the exterior surface  48  of tubular  36 . Preferably, second flow passage  32   b  is in fluid communication with first flow passage  32   a  so that flow through the system of passages  32  from first port  54  sequentially encounters second port  56  and then third port  58  for discharge of fluid into the wellbore  16  as will be described. 
         [0018]    A second relief valve  34   b  is disposed in second passage  32   b . In certain preferred embodiments, valve  34   b  is adjacent third port  58 . 
         [0019]    Finally, surge relieve system  30  includes a valve  60  to block back flow along the annulus of the drill string  24 . In certain preferred embodiments, valve  60  is a non-return valve, such as a float valve, ball valve, flapper valve or the like, that is actuated by backflow through the drill string  24 . In certain preferred embodiments, valve  60  is positioned in the annulus  42  of tubular member  36 , preferably adjacent the first end  38  uphole of passage  32   b  and relief valve  34   b.    
         [0020]    With on-going reference to  FIG. 2 , surge relief system  30  may also include a third flow passage  32   c . Although it may be defined in drill bit  28  in certain embodiments, preferably third flow passage  32   c  is disposed in tubular  36  between the first end  38  and second end  40  and uphole of second flow passage  32   b . Third flow passage  32   c  has a forth port  62 . Forth port  62  is preferably positioned between the first and second ends  38 ,  40 , respectively, of tubular  36 . In preferred embodiments, forth port  62  is uphole from third port  58  and defined in the exterior surface  48  of tubular  36 . Preferably, third flow passage  32   d  is in fluid communication with first flow passage  32   a  and second flow passage  32   b  so that flow through the system of passages  32  from first port  54  sequentially encounters second port  56 , then third port  58  and then forth port  62  for discharge of fluid into the wellbore  16  as will be described. In this regard, as illustrated in the embodiment of  FIG. 2 , first, second and third passages  32   a ,  32   b ,  32   c , respectively, are in fluid communication with the internal annuli  42 ,  52 . In certain preferred embodiments, portions of the annuli form a parts of the respective first, second and third passages  32   a ,  32   b ,  32   c . Likewise, as shown in  FIG. 3 , one or more of the passages  32   a ,  32   b ,  32   c  may form a portion of an overall passage  34 . 
         [0021]    A third relief valve  34   c  is disposed in third passage  32   c . In certain preferred embodiments, valve  34   c  is adjacent forth port  62 . 
         [0022]    Moreover, the passages  32   a ,  32   b  and  32   c , may be angled relative to the axis of the drill string  24  to control flow of the wellbore fluid therethrough. For example, as illustrated by passage  34   a , a passage may be angled uphole so that uphole movement of the drill string will drive wellbore fluid through port  56  into the passage, down and out through the first port  54 . Likewise, as shown in  FIG. 3 , passage  32   c  is oriented axially upward so that uphole movement of the drill string will drive wellbore fluid through port  62  into the passage, down and out through the first port  54 . 
         [0023]    As illustrated in  FIG. 3 , surge relief system  30  may also include a fourth passage  32   d  isolated from the first, second and third passages  32   a ,  32   b ,  32   c . Fourth passage  32   d  is preferably disposed in drill bit  28  and includes a fifth port  64  and a sixth port  66 . In certain preferred embodiments, fifth port  64  is axially disposed so as to open towards the bottom of wellbore  16  when drill bit  28  is positioned therein. Fourth passage  32   d  may include a fourth relief valve  34   d  disposed along fourth passage  32   d  between the fifth and sixth ports  64 ,  66 . 
         [0024]    With on-going reference to  FIG. 3 , a surge relief system  30  similar to that of  FIG. 2  is illustrated, but where one or more passages  34  are isolated from fluid communication with annulus  42 . This may be the case where annulus  42  is part of another system, such as a mud motor  68  as shown in  FIG. 3 . 
         [0025]    In certain preferred embodiments, surge relieve valves  34   a ,  34   b  and  34   c  may have adjustable activation pressures or otherwise may be selected to activate upon a certain pressure threshold. 
         [0026]    Preferably, activation pressures for all of the valves  34  would be higher than the mud circulating pressure utilized during drilling. Moreover, the activation pressures for valves  34   a ,  34   b ,  34   c  may be set to sequentially higher activation pressures. For example, the activation pressure of valve  34   a  may be lower than the activation pressure of valve  34   b , which may likewise be lower than the activation pressure of valve  34   c . Thus, as flow induced by heave progresses axially along the passage  34  system from first port  54 , the activation pressures for valves  34  becomes increasingly higher, thereby permitting the flow to be managed. In this regard, one or more transducers  70  may be disposed in the passages  34  and valves may be activated utilizing a control system  72  either positioned locally or at the surface. Additional valves  34  in additional flow passages may likewise be selected to activate based on a predetermined fluid pressure. Finally, surge relieve valves  34  may be one-way or two-way. As described below, in certain embodiments of the disclosure, flow through the valve in one direction is utilized to minimize the effects of surge on the formation, while flow through the valve in the opposite direction is utilized to minimize the effects of swab on the system. 
         [0027]    Thus, to utilize a surge relief system  30  during the drilling of a wellbore from an offshore floating platform, a drill string  24  having a BHA  26  and drill bit  28  with the surge relief system  30  is positioned in a wellbore  16 . The system is utilized during periods when drilling, i.e., engagement of a drill bit with the formation, has been suspended. In this regard, the system is most useful during dripping of the drill string into or out of the wellbore. During such a process, downward heave on the drill string resulting from wave action will force the drill bit down into the wellbore fluid. The wellbore fluid will be forced through the first port and driven into the first passage. Once the pressure of this fluid in the first passage reaches a predetermined threshold, the first relief valve is actuated, allowing the flow to pass through the second port and back out into the wellbore. Likewise, as wellbore fluid is driven into the second passage, and then the third passage, the second and then the third relieve valves will actuate, to allow the flow to pass through the corresponding ports back out into the wellbore. 
         [0028]    To the extent this flow passes into the lower annulus, the backpressure valve can be activated to prevent the fluids from passing pack up the drill string. 
         [0029]    Likewise, as upward heave on the drill string pulls the drill bit and BHA upward, wellbore fluid can pass through the second, third and fourth ports into the surge relief system where the fluid can be forced out of the first port in the drill bit, thereby minimizing the creation of low pressure in the wellbore by virtue of a sudden upward movement of the drill string. 
         [0030]    Although the number, locations and orientations of the various flow passages and ports have been illustrated herein, certain embodiments of the disclosure are not limited to the illustrated numbers, positions and orientations so long the overall surge relieve system  30  is disposed to pass flow of wellbore fluids through the system of one or more passages and ports to minimize the effects of surge and swab in the wellbore. Thus, flow passages may take various shapes or routes through the BHA and drill bit. Likewise, ports for the flow passages may be positioned at a number of locations along the overall BHA/drill bit assembly without limiting the disclosure. 
         [0031]    While the foregoing disclosure is directed to the specific embodiments of the disclosure, various modifications will be apparent to those skilled in the art. It is intended that all variations within the scope and spirit of the appended claims be embraced by the foregoing disclosure.