Abstract:
A method of well logging in which the logging tool is delivered to the bottom of the well within a drill pipe and then the well is logged by withdrawing the drill pipe with the sensor portion of the logging tool protruding from the drill pipe. Following the logging operation, the logging tool is returned to the surface by reverse circulation.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a well logging method and apparatus and more particularly to a method and apparatus which enables efficient and rapid logging of a well. 
     In oil and gas exploration it is extremely important to produce logs of each well in order that the oil/gas producer can assess the potential output of the well and know where to perforate. 
     Whilst such well logging is beneficial, it can be extremely expensive due to several factors, one of which is the time taken to produce the log. 
     When logging a well the drilling rig is required to stand idle from its drilling operation. The hire cost of such offshore rigs is very expensive and time taken to acquire data from conventional well logging of horizontal holes can be several days. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a well logging method and apparatus which enables a well to be logged in a much shorter time period than is possible with conventional methods. 
     It is a further object of the present invention to provide a well logging method and apparatus which is applicable to small diameter short length logging tools. 
     The present invention provides a method of well logging comprising the steps of: 
     a) inserting a battery powered memory logging device into a well borehole at a head end of said well, said well borehole containing a drill pipe; 
     b) forcing said logging device to a position adjacent to the far end of said drill pipe, opposite to said head end, by means of pump pressure applied to said logging device, said pump pressure being applied along said drill pipe from said head end; 
     c) maintaining pump pressure on said logging device; 
     d) pulling back on said drill pipe over a defined length whilst maintaining said pump pressure to expose at least a portion of the logging tool containing logging sensors into the open borehole at the end of the drill pipe; 
     e) pulling said drill pipe through said borehole towards said head end; 
     f) maintaining the pump pressure to maintain the position of the logging portion of the logging device protruding from the end of the drill pipe; and 
     g) logging the characteristics of the well with said logging device as said drill pipe is pulled through said well borehole. 
     Preferably the method further comprises the steps of: 
     h) once logging of the borehole over a required distance has been completed, reversing the pump pressure in said drill pipe such that pump pressure is applied to the end of said logging device furthest from said well head; 
     i) forcing said logging tool along said borehole towards said well head; and 
     j) catching said logging tool at a position adjacent said well head. 
     Preferably said method further comprises k) removing said logging device from said well head and down-loading said recorded logging data. 
     The invention also provides a well logging tool for use with the above method, said well logging tool comprising a first portion comprising well logging sensors and a second portion comprising a retention portion, said retention portion being provided with collar means for retaining said logging device within said drill pipe. 
     Preferably said retention portion of said well logging tool includes means for passage of fluid through said tool. 
     Conveniently the well logging tool is constituted as an open hole battery memory tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows diagrammatically a typical gas or oil well. 
     FIG. 2 shows diagrammatically a drill pipe end. 
     FIG. 3 diagrammatically shows the head end of the well of figure (in greater detail). 
     FIG. 4 shows the logging tool at a first initial position at the bottom of the drill pipe of the well of FIG.  1 . 
     FIG. 5 shows the logging tool at a second position at the bottom of the drill pipe of the well of FIG.  1 . 
     FIG. 6 shows the logging tool at a third position at the bottom of the drill pipe with the drill pipe moved away from the well end. 
     FIG. 7 shows the logging tool in a fourth position with the drill pipe moved further away from the well end. 
     FIG. 8 shows the logging tool in a fifth position with the logging tool in a sixth position being returned to the well head end by reverse fluid pressure. 
     FIG. 9 is a flow diagram showing an example of a process for using the logging tool of the present invention within a drill pipe of a well. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to the drawings, FIG. 1 shows diagrammatically a well  10 . The well  10  will be typically an oil or gas well and may comprise a vertical portion  12  and possibly a horizontal portion  14 . The well  10  may extend for several thousand feet. 
     The well  10  comprises a head end  16  and a “bottom” end  18 . The term bottom end is used, but as can be seen from FIG. 1, the well  10  can extend horizontally or even turn slightly upwards. Thus, the term bottom is used to mean the opposite end of the well  10  to the head end  16 . 
     FIG. 2 shows diagrammatically the bottom end  18  of the well  10  in greater detail. A drill pipe  20  is shown which reaches to the bottom end  18  of the well  10 . The sides of the well  10  are indicated at  22 . The drill pipe will normally have a shoulder portion  24 . As indicated by arrows  26 , fluid, usually a carefully controlled mud mixture, is circulated down the central bore of the drill pipe  20  and back up the outside volume between the drill pipe  20  and the side  22  of the borehole. The fluid may be supplied by fluid pump and reservoir means  17  (FIG.  1 ). The supply of fluid is well known in the control/drilling of boreholes and thus the supply system will not be described further. 
     FIG. 3 shows diagrammatically the well head in greater detail. This comprises a catch portion  30  which is shown to be of undetermined length. 
     With reference now to FIG. 4, a typical logging tool  40  is shown positioned at the bottom end  18  of the well  10 . 
     The logging tool  40  has been previously positioned at the head end  16  of the well  10  and then by using the pump fluid pressure in the direction of arrow  26  the logging tool  40  is forced down the drill pipe  20  until the end of the logging tool  40  reaches the bottom end  18  of the well  10  where its progress is halted as shown in FIG.  4 . 
     In a preferred example, the logging tool  40  comprises a first portion  42  comprising well logging sensors and calliper/drive systems, and a second portion  44  including a catch portion  46  which acts as a fishing neck. 
     The second portion  44  preferably includes means for allowing controlled fluid flow  26  through said portion  44  with fluid passing into openings  47  and out of openings  48  or vice versa. A full description of the fluid control section of tool  40  is provided in a copending patent application having the U.S. Ser. No. 09/449,057, filed on Nov. 24, 1999, and thus this description is hereby incorporated by way of reference. 
     The method of operation is as follows and is illustrated by FIGS. 4 to  8 . In FIG. 4, the logging tool  40  has been forced by fluid flow  26  to the bottom end  18 . 
     Once the logging tool  40  has reached the bottom of the well  10 , the tool  40  will be retained at the end of the drill pipe  20 . The fluid pressure will then begin to build up on the end of the logging tool  40 . The system is designed to allow pumping pressure to build to a predetermined limit, which in a preferred embodiment is 100 p.s.i. At this pressure a differential valve (not shown) will open in section  44  of logging tool  40  allowing the continuation of the flow  26  but now via the tool  40  (see FIG.  6 ). 
     The fluid flow pressure  26  is maintained and the drill pipe  20  is then moved back (FIG. 5) towards the well head by a distance ‘d’ (or greater) which causes the logging section  42  of logging tool  40  to protrude from the bottom end of the drill pipe  20 . 
     The movement of the drill pipe  20  is by conventional means and will not be described in detail. 
     The free end of the interior of drill pipe  20  frictionally engages a collar  52 , of per se known design, located uphole of the openings  48 . Such engagement prevents the logging tool from emerging completely from the end of drill pipe  20 . 
     As shown in FIG. 6, calliper  45  will open when the logging section  42  of tool  40  enters the borehole  22  and then logging will commence with drill pipe  20  being pulled at a known rate towards the well head  16 . Calliper control will be by using the Induction measurement and Casing Collar Locator (CCL). 
     Logging of the open borehole  22  will then continue as the drill pipe  20  is withdrawn until the casing shoe  23  is reached, at which stage the calliper arm  45  will close (FIG.  7 ), again by use of Induction measurement and Casing Collar Locator. 
     The logging operation is then completed with the data being recorded inside the logging tool  40 . 
     A repeat section can be made once the calliper  45  has closed. 
     The mud flow  26  is then reversed as indicated by arrows  260  and this reverse mud flow will lift the tool string incorporating the logging tool  40  and the tool  40  will be received and captured in holding device  30 ,  23 . 
     With appropriate reverse flow pressures, the tool  40  may be received at the well head from a depth of 10,000 ft in approximately 50 minutes and data can be downloaded in approximately 10 to 20 minutes. 
     The method according to the present invention has several advantages over known systems. 
     Firstly, by forcing the logging tool  40  to the bottom of the well  10  inside the drill pipe  20 , the tool  40  is protected from any wash-out regions as it passes down the pipe  20 . 
     When the logging tool  40  reaches the end of the drill pipe  20 , it is still fully within the drill pipe  20 . The drill pipe  20  is withdrawn from the logging tool  40 , the logging tool  40  thereby remaining stationary relative to the well  10 . The calliper  45  and the sensoring end of the logging tool  40  will therefore not have to be forced into an open bore and therefore will be protected at all times. 
     By use of the differential valve means, the fluid flow can be maintained during logging. 
     Referring to FIG. 9, a flow diagram of an example of a process for using the logging tool  40  of the present invention within the drill pipe  20  of the well  10  is shown. FIGS. 4-8 shows the different positions of the logging tool  40  during this process. First, wash the drill pipe  20  at ‘TD’. Then, introduce the logging tool  40  and pump sub into the drill pipe  20 , and pump the logging tool  40  to ‘TD’. Then, increase the pump pressure to 100 lbs. and the differential valve (not shown) will open. The flow will establish approximately 600 lbs. compression on the logging tool  40 . Maintain the pump pressure and pull back the drill pipe  20  for length of the logging tool  40 . This will lay the logging tool  40  at ‘TD’ in open hole. The calliper  45  will open when wash pipe passes over CCL. Continue to pull the drill when logging is in process. The calliper arm  45  closes as CCL passes the casing shoe. Now, reverse the mud flow. 70 p.s.i. will lift the logging tool  40 . Then, prepare to receive the logging tool  40  at the surface. It will take approximately 30 minutes from 10,000 feet. Then, download the data, which will take approximately 2 to 3 minutes. Then, check the quality of the data. 
     For the example of the process described above, the control parameters are: in a 2.75″ ID drill pipe; mud pressure*5.9−tool weight/5.9=force applied to SONDE; flow rate/internal volume per foot=tool speed; and volume pumped/interval volume per foot=distance traveled (4′/gallon).