Patent Publication Number: US-6702041-B2

Title: Combined logging and drilling system

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system for drilling and logging of a wellbore formed in an earth formation. The invention furthermore relates to a drill string, a logging tool string and a logging collar for use in conjunction with the system of the invention. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5589825 discloses a system whereby a logging tool string is lowered through the longitudinal fluid channel of the drill string until the logging tool is located opposite a number of windows provide in the wall of the drill string. Logging signals pass from the logging tool through the windows into the earth formation. Only limited logging information can be obtained with this known system, due to the limited size of the windows. Furthermore, this system requires precise positioning of the logging tool relative to the windows. 
     U.S. Pat. No. 3112442 discloses a system whereby a logging tool passes through the fluid channel of a drill string until a number of electrodes of the tool pass through the fluid nozzles of the drill bit to below the drill bit. The electrodes are of limited size and have limited capacity for emitting and receiving logging signals. Another drawback of this system is that passage of the electrodes through the nozzles can be hampered by the shape and direction of the nozzles. Furthermore, in case the lower end part of the drill string contains Measurement While Drilling equipment (MWD) or a hydraulic downhole motor, lowering of the logging tool string to the drill bit is virtually impossible. 
     It is an object of the invention to provide a system for drilling and logging of a wellbore formed in an earth formation, which overcomes the drawbacks of the known systems, and which is robust and provides adequate logging information without hampering drilling operations. 
     It is another object of the invention to provide a drill string for use in conjunction with the system of the invention. 
     It is a further object of the invention to provide a logging tool string for use in conjunction with the system of the invention. 
     It is yet another object of the invention to provide a logging collar for use in conjunction with the system of the invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a system for drilling and logging of a wellbore formed in an earth formation, the system comprising a drill string provided with an external recess extending in longitudinal direction of the drill string, a fluid passage for flow of drilling fluid from an upper end of the drill string to a lower end thereof, and a port providing fluid communication between the fluid passage and the recess, the system further comprising a logging tool string capable of passing through the fluid passage and from the fluid passage via the port into the recess, and a removable closure element adapted to selectively close the port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows a drill string applied in an embodiment of the system according with to the invention. 
     FIG. 1A schematically shows a logging collar of the embodiment of FIG.  1 . 
     FIG. 2 schematically shows cross-section  2 — 2  of FIG.  1 A. 
     FIG. 3 schematically shows cross-section  3 — 3  of FIG.  1 A. 
     FIG. 4 schematically shows a detail of FIG. 1A whereby a logging tool string has been lowered into the logging collar. 
     FIG. 5 schematically shows the logging collar of FIG. 1A whereby the logging tool string has been further lowered. 
     FIG. 6 schematically shows cross-section  6 — 6  of FIG.  5 . 
     FIG. 7 schematically shows cross-section  7 — 7  of FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     By lowering the logging tool string through the fluid passage and removing the closure element, the logging tool string can be moved via the port into the external recess where the logging tool string becomes exposed to the exterior of the drill string. Subsequently the logging tool string is induced to conduct logging measurements, whereafter the logging tool string is retrieved into the fluid passage of the drill string. An important advantage of the system of the invention is that the recess can be located above certain drill string equipment present in the downhole assembly, such as MWD equipment or a downhole motor for driving the drill bit, so that lowering of the logging tool string is not hampered by the presence of such equipment. 
     Suitably the logging tool string is provided with connecting means for selectively connecting the logging tool string to the closure element. 
     Preferably the connecting means forms a secondary connecting means, and the closure element is provided with primary connecting means for selectively connecting the closure element to the drill string. 
     In an attractive embodiment, the drill string is provided with guide means for guiding the closure element along the recess in longitudinal direction thereof. 
     Suitably the guide means includes a pair of substantially parallel edges extending in longitudinal direction of the drill string, each edge forming a transition between the outer surface of the drill string and the recess. 
     The invention will be further described in more detail and by way of example with reference to the accompanying drawings in which like reference numerals relate to like components. 
     Referring to FIG. 1 there is shown a drill string  1  extending from a drilling rig  2  at the earth surface  3  into a wellbore  4  formed into an earth formation  5 , the drill string  1  having a drill bit  6  arranged at the lower end thereof and a longitudinal fluid passage (not shown) for flow of drilling fluid from the drilling rig  2  to the drill bit  6 . The lower end part of the drill string  1  includes a plurality of conventional drill string collars (not shown) and a logging collar  8  interposed between an upper part  10  of the drill string  1  and a lower part  12  of the drill string  1 , which lower part  12  includes a downhole motor (not shown) for driving the drill bit  6 . 
     In FIGS. 1A,  2  and  3  is shown in more detail the logging collar  8  which includes an upper connector  14  for connecting the logging collar  8  to the upper drill string part  10  and a lower connector  16  for connecting the logging collar  8  to the lower drill string part  12 . The longitudinal fluid passage of the drill string  1  continues through the logging collar  8  in the form a channel  18  passing through the logging collar  8  throughout the length thereof. The logging collar  8  is provided with a recess  20  extending in longitudinal direction thereof, and a port  22 . The port  22  is in direct fluid communication with the recess  20  and with the passage  18  via a bore  23  formed in the logging collar  8 . The recess  20  defines a pair of substantially parallel edges  24   a ,  24   b  extending in longitudinal direction of the drill string  1 , each edge  24   a ,  24   b  forming a transition between the outer surface of the drill string  1  and the recess  20 . A removable closure element  24  is located in the port  22 . 
     Referring further to FIG. 4 there is shown a detail of the logging collar  8  including the port  22  and the closure element  24 . The closure element  24  comprises an insert member  26  of frustoconical shape so as to allow removal of the insert member  26  from the port  22  in outward direction thereof, the port  22  and the insert member  26  having respective complementary contact surfaces  28 ,  28 ′. A guide element  29  is connected to the insert member  26  at the side thereof facing the recess  20 , which guide element  29  will be described in more detail hereinafter with reference to FIG.  7 . The closure element  24  furthermore comprises a primary latching device  30  including a post  32  extending into the bore  23 . The post  32  is near the upper end thereof provided with an annular recess  34 . A cylindrical cage  36  is connected to the insert member  26  by threaded connection  8  and extends concentrically around the post  32  with an annular space  40  between the cage  36  and the post  32 . A cylindrical sleeve  42  extends in the annular space  40 , the sleeve being slideable along the post  32  and being biased away from the insert member  26  by a spring  44 . The cage  36  retains four metal locking balls  46  which extend into four locking recesses  48  provided in the wall of the bore  23 . The sleeve  42  is provided with four releasing recesses  50  into which the locking balls  46  fit when the sleeve  42  is biased a sufficient distance against the force of the spring  44 . For the purpose of clarity, only two locking balls  46 , two locking recesses  48  and two releasing recesses  50  are shown. 
     A logging tool string  52  extends from surface via the longitudinal channel  18  into bore  23 , the logging tool string  52  including a set of logging tools (referred to hereinafter), a power unit (not shown) and an electronic memory unit (not shown). The logging tool string  52  is assembled from a plurality of mutually hingeable sections  53  capable of passing through the passage  18  and from the passage  18  via the bore  23  into the recess  20 . The logging tool string  52  includes a secondary latching device  54  arranged at the lower end of the logging tool string  52 , the secondary latching device  54  having an interior space  55  of circular cross-sectional shape and of diameter corresponding to the overall diameter of the post  32  so that the post  32  fits into the interior space  55 . The secondary latching device  54  is internally provided with four locking dogs  56  (only two of which are shown) capable of pivoting about pivoting points  57 . A spring  58  is wound around the locking dogs  56  so as to bias the end parts of the locking dogs  56  facing the post  32 , towards each other. The secondary latching device  54  is furthermore provided with a landing member  59  extending into the interior space  55  and having a landing surface  60  arranged such that when the post  32  extends into the interior space and contacts the landing surface  60 , the locking dogs  56  are received in the annular recess  34  of the post  32 . Furthermore, the secondary latching device  54  has a lower end surface  62  arranged at a longitudinal distance from the landing surface  60  such that when the landing surface  60  contacts the post  32 , the lower end surface  62  biases the sleeve  42  to the position whereby the releasing recesses  50  are located opposite the respective locking balls  46 . 
     In FIGS. 5,  6  and  7  is shown the logging collar  8  whereby the logging tool string  52  extends from the channel  18  via the bore  23  into the recess  20 . The logging tool string  52  includes the insert member  26  referred to hereinbefore, and furthermore a density logging tool  64  biased against the borehole wall by a calliper  66 , a seal member  68  and a hydraulic pumping sub  70 . The hydraulic pumping sub  70  is located in the channel  18  and is adapted to pump the logging tool string  52  through the drill string  1  into the logging collar  8 , and the seal member  68  is located in the bore  23  and is adapted to thereby seal the bore  23 . 
     Referring more specifically to FIG. 7 there is shown the insert member  26  with the guide element  29 . As shown, the guide element  29  bridges the gap between the edges  24   a ,  24   b  and has opposite end surfaces of a shape substantially complementary to the shape of the edges  24   a ,  24   b  so that the guide element  29  is allowed to be guided in longitudinal direction along the edges  24   a ,  24   b  while being prevented from substantial radial movement relative to the logging collar  8 . 
     During normal operation the drill string is operated to drill a new wellbore interval (not shown). During drilling the sleeve  42  is biased by spring  44  to the position shown in FIG. 4 so that the locking balls  46  are forced by the sleeve  42  into the respective locking recesses  48  provided in the wall of the bore  23 , thereby latching the insert member  26  to the logging collar  8 . 
     After drilling of the wellbore interval is completed the logging tool string  52  is lowered through the channel  18  of the drill string  1  by pumping the pumping sub  70  in downward direction through the channel  18 , until the secondary latching device  54  moves into the bore  23 . Subsequently the logging tool string  52  is further lowered so that the post  72  enters into the space  55  and contacts the landing surface  60  of the landing member  59 . Simultaneously the lower end surface  62  of the secondary latching device pushes the sleeve  42  against the force of the spring  44  until the releasing recesses  50  become located opposite the respective locking balls  46 . In this position the sleeve  42  no longer forces the locking balls  46  into the locking recesses  48  so that the insert member  26  becomes unlatched from the logging collar  8 . Simultaneously the locking dogs  56  become engaged in the annular recess  34  of the post  32  and thereby latch the logging tool string  52  to the insert member  26 . The logging tool string  52  with the insert member latched thereto is then further lowered through the recess  20  whereby the guide element  29  is guided in longitudinal direction along the edges  24   a ,  24   b  and is prevented from radial movement relative to the logging collar  8 . Lowering of the logging tool string  52  is stopped when the seal member  68  becomes located in the bore  23  and thereby seals the bore  23  The density logging tool  64  is then operated to conduct a logging measurement whereby the logging date are stored in the electronic memory unit. 
     After logging is completed, the logging tool string  52  is lifted until the insert member  26  enters the port  22 . The logging tool string  52  is then further lifted thereby unlatching the locking dogs  56  from the annular recess  34  and allowing the sleeve  42  to slide along the post  32  away from the insert member  26  by the action of the spring  44 . The sleeve  42  thereby forces the locking balls  46  into the respective locking recesses  48  so that the insert member  26  becomes latched to the logging collar  8  and covers the port  22 . 
     A further wellbore interval can then be drilled and logged in the manner described above, or the drill string  1  can be retrieved to surface if necessary. 
     Instead of lowering the logging tool string by pump-down technique, the string can be lowered by wireline or by a combination of wireline and pump-down technique. Lifting of the logging tool string can be done by wireline, by reverse pumping (i.e. pumping fluid from the annular space between the drill string and the wellbore wall/casing into the drill string), or by a combination thereof. 
     The logging data stored in the electronic memory unit can be retrieved after retrieval of the logging tool string to surface, after retrieval of the drill string with the logging tool string contained therein to surface, or by transferring the logging data from the electronic memory unit to surface using suitable signal transfer means while the logging tool string is still located downhole.