Method and system for determining core orientation

Abstract

A method ( 60 ) of determining core orientation of a core sample ( 12 ) cut from the ground by a drill rig ( 10 ) having a drill string and a drill bit ( 20 ) coupled to a downhole end of the drill string. Drilling data (Cn, Rn) is continuously acquired while the drill rig ( 10 ) is operating to cut and retrieve the core sample ( 12 ). The drilling data is a combination of core orientation data Cn and rig operational data Rn, where the rig operational data is constituted by either one or both of: (a) near bit rig data Nn; and, (b) at surface rig data Sn. The drilling data is analyzed for a specific pattern of rig operational data Rn indicative of the core sample being broken from ground by operation of the drill rig ( 10 ). On detection of the specific pattern, the orientation of the core sample prior to being broken from the ground is the acquired core orientation data Cn coinciding with that specific pattern of rig operational data Rn.

1 . A method of determining core orientation of a core sample cut from the ground by a drill rig having a drill string and a drill bit coupled to a downhole end of the drill string, the method comprising:
 continuously acquiring drilling data, while the drill rig is operating to acquire the core sample wherein the drilling data is a combination of core orientation data and rig operational data, wherein the rig operational data is constituted by both of: (a) near bit rig data; and, (b) at surface rig data; and   analyzing the drilling data for a specific pattern of rig operational data indicative of the core sample being broken from ground by operation of the drill rig and on detection of the specific pattern determining orientation of the core sample prior to being broken from the ground using the acquired core orientation data.   
     
     
         2 . The method according to  claim 1 , wherein acquiring the drilling data comprises acquiring the drilling data at least for a period which includes a continuous period from commencement of operation of the drill rig to cut the core sample to any event occurring after commencement of operating the drill rig to break the core sample from in situ strata. 
     
     
         3 . The method according to  claim 2 , wherein the event is applying pull-up to the drill string to affect the breaking of the core sample from in situ strata. 
     
     
         4 . The method according to  claim 2 , wherein the event is retrieval of the core sample through the drill string. 
     
     
         5 . The method according to  claim 2 , wherein the event is extraction of the core sample from the drill string. 
     
     
         6 . The method according to  claim 2 , wherein acquiring the drilling data includes acquiring, during the operation of the drill rig to break the core sample, rig operational data relating to relative rotational motion between the core sample and an inner core tube supported by the drill string and into which the core sample advances during drilling. 
     
     
         7 . The method according to  claim 6 , comprising compensating the core orientation acquired upon the occurrence of the specific pattern to account for the relative rotational motion and using the compensated core orientation as the core orientation of the core sample cut by the drill rig. 
     
     
         8 . The method according to  claim 1 , wherein the core orientation data includes dip and azimuth of a known reference datum on or transferable to the core sample. 
     
     
         9 . The method according to  claim 1 , wherein the rig operational data comprises any one, or any combination of any two or more, of: rotational speed of the drill string, displacement of the drill string in an up hole direction; displacement of the drill string in a down hole direction; ambient fluid pressure; the existence of fluid flow in the drill string; rate of fluid flow into a bore hole; vibration in the drill string; mechanical shock; rate of penetration, hole depth; number of drill pipe joints passed when a data acquisition tool (DAT) is transported down the drill string or retrieved from the drill string or both; latent torque in the drill string; weight on bit; and torque on bit. 
     
     
         10 . The method according to  claim 1 , wherein the specific pattern of drilling data comprises data indicative of: (a) cessation of rotation of the drill string; and subsequently: (b) application of pull-up to the drill string. 
     
     
         11 . The method according to  claim 10 , wherein the specific pattern of rig operational data comprises, subsequent to the occurrence of the application of pull-up, data indicative of (c) vibration arising from impact of an overshot with a head assembly of an inner core barrel assembly containing the core sample cut by the drill rig. 
     
     
         12 . The method according to  claim 1 , comprising storing the acquired drilling data on a memory device which is disposed near the drill bit while the drill rig is in operation cutting the core sample. 
     
     
         13 . The method according to  claim 1  wherein core orientation data and near bit rig data are electronically communicated to an at surface electronic device or system either (a) while the drill rig is in operation cutting the core sample; or (b) while the core sample is within the drill string; or (c) at the surface after retrieval of the core sample. 
     
     
         14 . The method according to  claim 1 , wherein analyzing the drilling data occurs: while the drill rig is in operation cutting the core sample; or, while the core sample is within the drill string; or after retrieval of the core sample. 
     
     
         15 . The method according to  claim 1 , comprising transporting a data acquisition tool (DAT) provided with one or more sensors capable of acquiring the core orientation data and the near bit rig data through the drill string toward the drill bit. 
     
     
         16 . The method according to  claim 1 , comprising continuously acquiring the core orientation data and rig operational data at a known sample rate. 
     
     
         17 . The method according to  claim 1 , wherein the at surface rig data comprises weight on bit. 
     
     
         18 . The method according to  claim 1  wherein determining the core orientation involves using one or more of the acquired core orientation data. 
     
     
         19 . The method according to  claim 18 , wherein determining the core orientation involves obtaining an average of a plurality of the acquired core orientation data. 
     
     
         20 . The method according to  claim 1 , wherein determining the core orientation data involves using one or more of the core orientation data acquired within a user selectable time period. 
     
     
         21 . The method according to  claim 20 , wherein the user selectable time period comprises a period of time selected from the group consisting of: (a) before the core sample is broken away from the ground; (b) after the core sample has been broken away from the ground; and (c) before and after the core sample has been broken away from the ground. 
     
     
         22 . A system for determining core orientation of a core sample cut from the ground by a drill rig having a drill string and a drill bit coupled to a downhole end of the drill string comprising:
 a data acquisition tool (DAT) wherein the DAT is arranged to continuously acquire core orientation data at least while the drill rig is operating to acquire the core sample; and   both of a (a) near bit rig data acquisition system arranged to continuously acquire near bit rig data (Nn); and, (b) at the surface rig data acquisition system arranged to continuously acquire surface rig data (Sn) while the drill rig is operating to acquire the core sample.   
     
     
         23 . The system according to  claim 22 , wherein the near bit rig data acquisition system is provided in the DAT. 
     
     
         24 . The system according to  claim 22 , further comprising a DAT tripping system capable of transporting the DAT through the drill string toward a toe of a hole drilled by the drill rig and subsequently retrieving the DAT from the drill string. 
     
     
         25 . The system according to  claim 22 , wherein the DAT comprises one or more core orientation sensors arranged to enable the DAT to acquire one or any two or more of: dip, azimuth, gravitational top or bottom of borehole, Magnetic Tool face or True North measurements of a known reference datum on or transferable to the core sample. 
     
     
         26 . The system according to  claim 22 , wherein the DAT comprises one or more near bit rig parameter sensors arranged to enable the DAT to acquire one, or any combination of any two or more, of the following drilling parameter data: rotational speed of the drill string, differential rotation between the drill string and an inner core barrel assembly, displacement of the drill string in an up hole direction; displacement of the drill string in a down hole direction; ambient fluid pressure; the existence of fluid flow through the drill string; rate of fluid flow into a bore hole; vibration; mechanical shock; rate of penetration, hole depth; number of drill pipe joints passed when the DAT is transported down the drill string or retrieved from the drill string, or both; torque when the drill string is drilling; or latent torque in the drill string. 
     
     
         27 . The system according to  claim 22 , wherein the DAT comprises an on-board memory to enable on-board storage of the acquired data. 
     
     
         28 . The system according to  claim 22 , wherein the DAT comprises a processor capable of processing the acquired data to produce processed downhole data. 
     
     
         29 . The system according to  claim 22 , comprising a telemetry system arranged to enable the DAT to communicate the acquired data in real time to an electronic device located at the surface. 
     
     
         30 . The system according to  claim 22 , comprising an inner core barrel assembly wherein the DAT is coupled to or housed within the inner core barrel assembly. 
     
     
         31 . The system according to  claim 22 , wherein the DAT comprises an event sensor arranged to automatically activate the DAT to continuously acquire one or more of the core orientation data, the surface rig data, and the near bit data in response to a sensed event pertaining to the lowering or locking of the DAT.