Magnetic ranging system for controlling a drilling process

Abstract

The invention relates to a ranging system ( 1 ) for controlling a drilling process downhole. The ranging system has a longitudinal direction and comprises a drilling tool ( 2 ) for drilling a first borehole ( 3 ), the drilling tool having a tool axis ( 4 ) and comprising a magnetic field source ( 5 ) in the form of an electromagnet generating a magnetic field ( 6 ) and having a magnetic field source axis ( 7 ) which is substantially parallel to the tool axis. Moreover, the ranging system comprises a sensing tool ( 8 ) arranged in a second borehole ( 9 ) for measuring the magnetic field by means of at least two sensor units ( 10 ), which sensor units are arranged at a distance (D) from each other along an axis of the sensing tool.

1 . A ranging system ( 1 ) for controlling a drilling process downhole, the ranging system having a longitudinal direction and comprising:
 a drilling tool ( 2 ) for drilling a first borehole ( 3 ), the drilling tool having a tool axis ( 4 ) and comprising a magnetic field source ( 5 ) in the form of an electromagnet generating a magnetic field ( 6 ) and having a magnetic field source axis ( 7 ) which is substantially parallel to the tool axis, and   a sensing tool ( 8 ) arranged in a second borehole ( 9 ) for measuring the magnetic field by means of at least two sensor units ( 10 ) wherein the sensor units are arranged at a distance (D) from each other along an axis of the sensing tool.   
     
     
         2 . A ranging system according to  claim 1 , wherein each sensor unit comprises at least one magnetometer ( 20 ). 
     
     
         3 . A ranging system according to  claim 1 , wherein the magnetic field source axis is substantially coincident with the tool axis. 
     
     
         4 . A ranging system according to  claim 1 , wherein the sensing tool is submerged into the well by a wireline. 
     
     
         5 . A ranging system according to  claim 1 , wherein the magnetometers are arranged in the same plane in the sensor unit. 
     
     
         6 . A ranging system according to  claim 5 , wherein the magnetometers measure the magnitude and direction of the magnetic field, such as the magnitude and direction of a local magnetic field vector. 
     
     
         7 . A ranging system according to  claim 1 , wherein the second borehole is an existing borehole. 
     
     
         8 . A ranging system according to  claim 1 , wherein the sensor unit and/or the drilling tool is driven by a driving unit ( 11 ). 
     
     
         9 . A ranging system according to  claim 1 , further comprising a positioning tool for determining the position of the sensing tool in the second borehole or the position of the drilling tool in the first borehole. 
     
     
         10 . A ranging system according to  claim 1 , wherein the sensing tool has means ( 12 ) for controlling and/or measuring the velocity or position of the sensing tool. 
     
     
         11 . A ranging system according to  claim 1 , wherein the magnetic field source has a through hole ( 13 ), allowing fluid for driving a drilling head ( 14 ) of the drilling tool to pass through the magnetic field source. 
     
     
         12 . A ranging system according to  claim 1 , further comprising a downhole calculation unit ( 15 ) for processing magnitude and direction measurements of the magnetic field measured by the sensing tool. 
     
     
         13 . A ranging system according to  claim 1 , further comprising a second drilling tool, the sensing tool being arranged in or in connection with the second drilling tool so that the first drilling tool comprises the magnetic field source and the second drilling tool comprises the sensing tool. 
     
     
         14 . A method for using the ranging system according to  claim 1 , comprising the steps of:
 drilling the first borehole in one drilling direction,   inserting the sensing tool into the second borehole,   measuring the magnitude and direction of the magnetic field while drilling,   calculating a position of the drilling tool relative to the sensing tool while drilling, and   calculating the direction of the drilling head,   
     
     
         15 . A method according to  claim 14 , further comprising the step of:
 adjusting the drilling direction based on the calculated direction and relative position of the drilling tool.   
     
     
         16 . Use of the ranging system according to  claim 1  downhole.