Core sample testing protocol

Abstract

The invention relates to the dividing up and testing of bulk samples from cores of rock. The method involves the extraction of several plugs for triaxial testing which are derived from exactly the same level in the core, and also Brazilian test samples and samples for compositional and textural analysis from the same level. Triaxial tests with different confining pressures may be performed to destruction on separate triaxial plugs, allowing a reliable full Mohr-Coulomb analysis to be performed. Mechanical properties may be related more reliably to composition and texture of rock. The technique is especially useful for non-conventional rock such as shale.

1 . A method of processing a bulk sample of a cylindrical rock core, the said bulk sample being created by making two transverse cuts through the core such that the bulk sample is of cylindrical shape with the same cross section as the core, having two end faces and a curved face, the method comprising:
 a) making a cut through the bulk sample, parallel to and spaced from the axis, to remove a slab from the bulk sample, thereby creating a plane face on the bulk sample extending parallel to the axis, the removed slab having a corresponding plane face;   b) removing from one of said end faces of the bulk sample three or more cylindrical plugs having substantially the same dimensions; and   c) performing triaxial compressive testing to failure on each of said plugs.   
     
     
         2 . A method according to  claim 1 , further comprising removing one or more disc shaped plugs either from said plane face of the bulk sample or from said corresponding plane face of the slab, at a location with respect to the length of the bulk sample which corresponds to that of the cylindrical plugs, and then subjecting said disc shaped plugs to Brazilian testing. 
     
     
         3 . A method according to  claim 2 , wherein at least two disc shaped plugs are subjected to Brazilian testing in respective different directions 
     
     
         4 . A method according to  claim 1  wherein one or more of the cylindrical plugs is subjected to CT scanning prior to triaxial testing. 
     
     
         5 . A method according to  claim 2 , wherein one or more of the disc shaped plugs is subjected to CT scanning prior to Brazilian testing. 
     
     
         6 . A method according to  claim 1  wherein two or more of said cylindrical plugs are subjected to respective different confining pressures during triaxial testing 
     
     
         7 . A method according to  claim 1  wherein a Mohr-Coulomb analysis is performed using the results from the triaxial testing. 
     
     
         8 . A method according to  claim 1  wherein one or more of the cylindrical plugs is subjected to CT scanning after triaxial testing to determine the type of mechanical failure. 
     
     
         9 . A method according to  claim 2  wherein one or more of the disc shaped plugs is subjected to CT scanning after Brazilian testing to determine the type of mechanical failure. 
     
     
         10 . A method according to  claim 1  wherein the axes of said cylindrical plugs are substantially parallel to the axis of the bulk sample. 
     
     
         11 . A method according to  claim 1  wherein the axes of two or more of said cylindrical plugs are at a non-zero angle to each other. 
     
     
         12 . A method according to  claim 11  wherein the axis of a first one of said cylindrical plugs is substantially parallel to the axis of the bulk sample and the axis of a second one of said cylindrical plugs is substantially perpendicular to the axis of the bulk sample. 
     
     
         13 . A method according to  claim 12  wherein the axis of a third one of said cylindrical plugs is inclined with respect to the axes of the first and second plugs. 
     
     
         14 . A method according to  claim 2  wherein a bulk sample carcass remains after said cylindrical and disc shaped plugs have been removed, and said carcass is subjected to analysis to determine one or more of:
 (a) matrix mineral composition; 
 (b) porosity 
 (c) pore space constituent; and 
 (d) total organic content. 
 
     
     
         15 . A method according to  claim 14 , further including the step of determining permeability. 
     
     
         16 . A method according to  claim 15 , wherein permeability is established by conducting one or more of:
 (a) Bulk density analysis;   (b) Grain density analysis;   (c) Gas filled porosity determination;   (d) Fluid saturation determination; and   (e) Effective total interconnected porosity determination.   
     
     
         17 . A method according to  claim 14 , further comprising thin section analysis to determine one or more of:
 (a) rock texture;   (b) grain size distribution; and   (c) degree of cementation.   
     
     
         18 . A method according to  claim 17 , further including petrographic analysis. 
     
     
         19 . A method according to  claim 18  wherein the analysis further includes identification of one or more of:
 (a) shale matrix composition; 
 (b) secondary cements; 
 (c) clays; 
 (d) pore types; and 
 (e) natural fractures. 
 
     
     
         20 . A method according to  claim 14 , wherein results from said analysis are correlated to results of said triaxial and/or Brazilian testing.