Downhole Sensor and Method of Coupling Same to A Borehole Wall

Abstract

Devices and methods for borehole seismic investigation are provided. The devices are a downhole tool having gripping devices which may improve contact between the downhole tool and the borehole wall (or casing of the borehole wall) and reduce slippage as compared to downhole tools without the gripping devices. The methods involve lowering a downhole tool having the gripping devices into a borehole and applying force to cause the gripping devices to penetrate or create an indentation in the borehole wall (or casing of the borehole wall). The methods and devices may improve the coupling between the downhole tool and surface to be monitored and/or may enhance the frequency range due to higher coupling frequency as compared to downhole tools without the gripping devices.

What is claimed is: 
     
         1 . A downhole tool for monitoring seismic waves, comprising:
 a. a housing comprising at least one gripping device adapted to puncture or create an indentation in a borehole wall or casing of a borehole wall, if the borehole wall is cased, when the at least one gripping device contacts the borehole wall and sufficient force is applied to the housing; and   b. at least one sensor integral with the housing.   
     
     
         2 . A downhole tool according to  claim 1 , wherein the at least one gripping device includes at least one protruding spike. 
     
     
         3 . A downhole tool according to  claim 1 , wherein the at least one gripping device is mounted to the housing. 
     
     
         4 . A downhole tool according to  claim 1 , wherein the at least one gripping device includes at least three gripping devices and the at least three gripping devices are arranged in a non-linear pattern on the housing. 
     
     
         5 . A downhole tool according to  claim 1 , wherein the at least one gripping device is three gripping devices which are arranged in a triangular geometry about the housing. 
     
     
         6 . A downhole tool according to  claim 1 , wherein the at least one gripping device is made of a material that is harder than the borehole wall or the casing of the borehole wall, if the borehole wall is cased. 
     
     
         7 . A downhole tool according to  claim 6 , wherein the material comprises tungsten carbide. 
     
     
         8 . A downhole tool according to  claim 1 , wherein the downhole tool has a coupling frequency of at least 1000 Hz. 
     
     
         9 . A downhole tool according to  claim 1 , wherein the at least one sensor is mounted on or within the housing. 
     
     
         10 . A method for coupling a sensor to a borehole wall, comprising:
 a. lowering a downhole tool into a borehole, wherein the downhole tool comprises a housing having at least one gripping device and at least one sensor;   b. contacting the at least one gripping device with a borehole wall; and   c. applying a sufficient force to the downhole tool to cause the at least one gripping device to penetrate or create an indentation in the borehole wall.   
     
     
         11 . A method according to  claim 10 , wherein the borehole wall is cased, and the penetration or indentation is in the casing of the borehole wall. 
     
     
         12 . A method according to  claim 10 , wherein the at least one gripping device includes at least three protruding spikes mounted to the downhole tool and arranged in a non-linear pattern, and contacting comprises contacting each of the three protruding spikes with the borehole wall, and applying comprises applying a sufficient force to cause each of the three protruding spikes to penetrate or create an indentation in the borehole wall. 
     
     
         13 . A method according to  claim 10 , wherein the force is applied by a clamping or locking mechanism. 
     
     
         14 . A method according to  claim 13 , wherein the clamping or locking mechanism is chosen from extendable mechanical arms, an inflatable bladder, bow springs and combinations thereof. 
     
     
         15 . A method according to  claim 10 , wherein the downhole tool is a bare sensor, a shuttle or a drill string tubular. 
     
     
         16 . A method according to  claim 10 , wherein the downhole tool is a shuttle or a drill string tubular and the at least one sensor is mounted on or within the shuttle or drill string tubular.