Sleeve for logging while drilling electromagnetic sensor

Abstract

An apparatus for measuring a characteristic of an earth formation includes a drill collar configured to be inserted into a borehole of the earth formation, an electromagnetic sensor on the drill collar, and a non-conductive sleeve surrounding a circumference of the drill collar including the electromagnetic sensor and configured to press directly against the electromagnetic sensor.

What is claimed is: 
     
         1 . An apparatus for measuring a characteristic of an earth formation, comprising:
 a drill collar configured to be inserted into a borehole of the earth formation;   an electromagnetic sensor on the drill collar; and   a non-conductive sleeve surrounding a circumference of the drill collar including the electromagnetic sensor and configured to press directly against the electromagnetic sensor.   
     
     
         2 . The apparatus of  claim 1 , further comprising:
 sealing members at axial ends of the non-conductive sleeve to form an airtight seal with respect to the drill collar and the non-conductive sleeve.   
     
     
         3 . The apparatus of  claim 2 , wherein the sealing members are located radially between the non-conductive sleeve and the drill collar. 
     
     
         4 . The apparatus of  claim 1 , wherein the non-conductive sleeve is a non-magnetic sleeve. 
     
     
         5 . The apparatus of  claim 1 , wherein the non-conductive sleeve is made of a polymer. 
     
     
         6 . The apparatus of  claim 1 , wherein the drill collar includes raised portions at axial ends of the non-conductive sleeve, the raised portions having diameters greater than a diameter of the non-conductive sleeve. 
     
     
         7 . The apparatus of  claim 6 , wherein the raised portions are made of a material having a hardness greater than a hardness of the drill collar. 
     
     
         8 . The apparatus of  claim 6 , wherein a distance from the ends of the non-conductive sleeve to the raised portions is less than a diameter of the non-conductive sleeve. 
     
     
         9 . The apparatus of  claim 1 , wherein the non-conductive sleeve is configured to press against substantially an entire outer radial surface of the electromagnetic sensor. 
     
     
         10 . The apparatus of  claim 1 , wherein the electromagnetic sensor is configured to press against the drill collar based on the non-conductive sleeve pressing against an outer radial surface of the electromagnetic sensor. 
     
     
         11 . An apparatus, comprising:
 a drill collar;   a sensor located around the drill collar; and   a non-conductive sleeve covering an entire outer surface of the sensor and configured to contact the outer surface of the sensor.   
     
     
         12 . The apparatus of  claim 11 , wherein the non-conductive sleeve forms an airtight seal with the drill collar. 
     
     
         13 . The apparatus of  claim 12 , further comprising sealing members located at axial ends of the non-conductive sleeve to press against the non-conductive sleeve to from the airtight seal with the drill collar. 
     
     
         14 . The apparatus of  claim 11 , wherein the non-conductive sleeve is configured to compress inwardly in a radial direction toward the sensor when a predetermined pressure is applied to the non-conductive sleeve. 
     
     
         15 . The apparatus of  claim 14 , wherein the predetermined pressure is one of a predetermined ranges of pressures corresponding to a pressure within a wellbore during a drilling operation. 
     
     
         16 . The apparatus of  claim 11 , wherein the non-conductive sleeve is made of a high-temperature rated plastic. 
     
     
         17 . The apparatus of  claim 11 , wherein the sensor is an electromagnetic sensor having a coil wound around the drill collar. 
     
     
         18 . The apparatus of  claim 11 , wherein a thickness of the non-conductive sleeve is at least 5% of the diameter of the non-conductive sleeve. 
     
     
         19 . The apparatus of  claim 11 , wherein the non-conductive sleeve has a smooth outer surface free of stress risers. 
     
     
         20 . A method, comprising:
 providing a drill collar in a wellbore, the drill collar including a sensor located on the drill collar and a non-conductive sleeve entirely covering the sensor; and   subjecting the non-conductive sleeve to a pressure to press the non-conductive sleeve against the sensor.   
     
     
         21 . The method of  claim 20 , wherein subjecting the non-conductive sleeve to the pressure includes performing a drilling operation in the wellbore. 
     
     
         22 . The method of  claim 21 , further comprising operating the sensor to obtain information about an earth formation while performing the drilling operation in the wellbore.