Sensor arrangement

Abstract

A sensor arrangement is described comprising a sensor housing (28), a first sensor (30) sensitive to a downhole parameter and carried by the housing (28), a second sensor (32) sensitive to the same downhole parameter as the first sensor (30) and carried by the housing (28), the second sensor (32) being spaced apart from the first sensor (30) by a fixed distance D in the axial direction of the housing (28), and a control unit (38) operable to monitor the outputs of the first and second sensors (30, 32) to ascertain information relating to the position, movement and/or related information of the housing (28). A related operating method is also described.

1 . A sensor arrangement comprising a sensor housing, a first sensor sensitive to a downhole parameter and carried by the housing, a second sensor sensitive to the same downhole parameter as the first sensor and carried by the housing, the second sensor being spaced apart from the first sensor by a fixed distance in the axial direction of the housing, and a control unit operable to monitor the outputs of the first and second sensors to ascertain information relating to at least one position, movement and related information of the housing. 
     
     
         2 . An arrangement according to  claim 1 , wherein the housing is incorporated into or attached to a bottom hole assembly, providing position information relating to the position of the bottom hole assembly, and/or is located elsewhere in a drill string. 
     
     
         3 . An arrangement according to  claim 1 , wherein the downhole parameter comprises temperature information. 
     
     
         4 . An arrangement according to  claim 1 , wherein the first and second sensors comprise one of thermoelectric generators and thermal cameras operable to produce an output indicative of a temperature difference between parts of the housing and an inner tubular member adjacent the respective sensors. 
     
     
         5 . An arrangement according to  claim 4 , wherein the first and second sensors together form a panoramic thermal camera. 
     
     
         6 . An arrangement according to  claim 5 , wherein the control unit undertakes an image processing technique to track the passage of a thermal feature through an image captured using the panoramic thermal camera. 
     
     
         7 . An arrangement according to  claim 1 , wherein position and/or related information derived by the control unit is supplied to at least one of (a) an operator at the surface and (b) a downhole located drilling control unit to allow directional drilling to lie undertaken autonomously. 
     
     
         8 . A sensing method comprising locating within a borehole a sensor arrangement as claimed in  claim 1 , and monitoring the outputs of the first and second sensors to identify when a feature previously detected by the first sensor is subsequently detected by the second sensor to determine that the sensor housing has moved by a distance equal to the spacing of the first and second sensors. 
     
     
         9 . A method according to  claim 8 , wherein the distance information is used to determine an axial velocity of the sensor housing. 
     
     
         10 . A method according to  claim 8 , and further comprising using the output of the first and second sensors, when undertaking a measurement whilst drilling survey, to confirm that at least one procedural step of the survey has been completed. 
     
     
         11 . A method according to  claim 10 , and further comprising using the output of the first and second sensors to detect the occurrence of a drill pipe connection procedure. 
     
     
         12 . A method according to  claim 8 , wherein the distance information is used to determine the occurrence of at least one of buckling, stretching and squat pipe conditions.