Method and apparatus for measuring in-situ rock moduli and strength

Abstract

An in-situ rock strength measurement tool features a sub that is integrated into a drill string, or other downhole tool string, and lowered into an uncased borehole. The sub includes a plurality of lateral pistons that are selectively extendable in a radial orientation to engage the wall of the borehole. The pistons exert a force against a defined area of the borehole wall and penetrate the borehole across the defined area. The force needed to penetrate the borehole may then be measured and used to calculate rock strength and to determine other formation properties.

1 . A rock strength measurement tool assembly for incorporation within a tool string and use within a borehole, the tool assembly comprising: 
 a generally cylindrical tool body having a pair of axial ends, the ends being configured for integrating the tool body within a tool string;    a piston member disposed within the tool body for reciprocal motion with respect thereto to selectively bring the piston member into contact with a borehole wall and penetrate the borehole wall; and    a mud motor disposed proximate the tool body and operably associated with the tool body for actuation of the piston member, the mud motor being actuated by flow of drilling mud within a tool string.    
     
     
         2 . The tool assembly of  claim 1  wherein there are multiple piston members that are axially aligned with one another upon the tool body.  
     
     
         3 . The tool assembly of  claim 1  wherein there are multiple piston members that are helically aligned with one another upon the tool body.  
     
     
         4 . The tool assembly of  claim 1  further comprising a sensing element for determining the amount of pressure force exerted by the piston upon a portion of borehole wall.  
     
     
         5 . The tool assembly of  claim 1  further comprising a sensing element for determining the amount of radial movement of the piston with respect to the tool body.  
     
     
         6 . The tool assembly of  claim 5  wherein the sensing element comprises a linear variable differential transducer.  
     
     
         7 . (Cancelled)  
     
     
         8 . (Cancelled)  
     
     
         9 . The tool assembly of  claim 1  wherein the tool body further comprises at least one mud channel extending between the axial ends of the tool body, the mud channel being sized to permit drilling mud to pass by the tool body within a wellbore.  
     
     
         10 . The tool assembly of  claim 1  wherein the tool body further includes at least one radially enlarged stabilizer portion opposite the piston upon the tool body and having a stabilizer surface for resting against the borehole wall during actuation of the piston body.  
     
     
         11 . (Cancelled)  
     
     
         12 . (Cancelled)  
     
     
         13 . The tool assembly of  claim 1  wherein the mud motor comprises a mud turbine and a power generator operably interconnected with the mud turbine to be actuated thereby.  
     
     
         14 . The tool assembly of  claim 13  wherein the power generator generates hydraulic fluid power.  
     
     
         15 . (Cancelled)  
     
     
         16 . A rock strength measurement tool assembly for incorporation within a tool string and use within a borehole, the tool assembly comprising: 
 a tool body having a pair of axial ends, the ends being configured for integrating the tool body within a tool string;    a piston member disposed within the tool body for reciprocal motion with respect thereto to selectively bring the piston member into contact with a borehole wall and penetrate the borehole wall;    a radially enlarged stabilizer portion presenting a stabilizer surface to rest against a wall of the borehole, the stabilizer portion lying opposite the piston member upon the tool body;    a mud motor disposed proximate the tool body and operably associated with the tool body for actuation of the piston member, the mud motor being actuated by flow of drilling mud within a tool string.    
     
     
         17 . The tool assembly of  claim 16  further comprising a radially enlarged central portion located between the axial ends and a radially reduced mud channel on the central portion to permit the passage of drilling mud past the central portion.  
     
     
         18 . The tool assembly of  claim 16  wherein the piston member is operably associated with a sensor for measurement of piston movement.  
     
     
         19 . The tool assembly of  claim 16  wherein the piston member is operably associated with a sensor for measurement of fluid pressure required to move the piston into penetrating contact.  
     
     
         20 . A method of determining rock strength comprising the steps of: 
 integrating a rock strength measurement tool into a drill string, the rock strength measurement tool comprising: 
 a tool body;  
 a piston member mounted within the tool body for reciprocating radial movement therein; and  
 a stabilizer portion lying opposite the piston member upon the tool body;  
   disposing the drill string within a wellbore to locate the rock strength measurement tool proximate a desired location within the wellbore;    radially moving the piston member outward from the tool body and into penetrating contact with the wellbore; and    determining the force required to move the piston into penetrating contact with the wellbore.    
     
     
         21 . The method of  claim 20  wherein the step of radially moving the piston into penetrating engagement with the borehole further comprises flowing drilling mud into a drill string to operate a mud motor, the mud motor, in turn providing power to move the piston.  
     
     
         22 . (Cancelled)  
     
     
         23 . (Cancelled)  
     
     
         24 . (Cancelled)