Systems and methods for classifying mechanical quality of a subterranean formation using measurements obtained during drilling

Abstract

Systems and methods for evaluating mechanical rock quality of subterranean formations include processing of mechanical rock property data to generate one or more corresponding mechanical quality metrics. The mechanical quality metrics may then be used, for example, to plan and execute subsequent drilling or completions (e.g., hydraulic fracturing) operations. In certain implementations, the mechanical rock property data is computed from drill bit vibration data collected during drilling of a wellbore through the subterranean formation.

1 . A method of classifying mechanical quality of material in subterranean formations comprising:
 with a processor, processing signal data to compute displacements of a drill bit, the displacements resulting from interaction of the drill bit with a material of a subterranean formation during drilling of a wellbore through the subterranean formation;   processing the displacements to compute a property of the material along the wellbore; and   generating a mechanical quality metric for a location within the material based on the computed property.   
     
     
         2 . The method of  claim 1 , wherein:
 the signal data includes acoustical signal data,   the signal data is stored on a non-transitory computer readable medium,   the signal data is measured using a sensor of a bottom hole assembly in operable communication with the non-transitory computer readable medium to store the signal data, and   processing the signal data comprises processing the acoustical signal data to obtain a property value representative of the property.   
     
     
         3 . The method of  claim 2 , wherein the signal data includes signal data corresponding to at least one of an axial acceleration of the drill bit, a lateral acceleration of the drill bit, a torsional acceleration of the drill bit, a centripetal acceleration of the drill bit, or a rotational acceleration of the drill bit. 
     
     
         4 . The method of  claim 2 , wherein processing the acoustical signal data to obtain the property comprises computing at least one of Poisson's ratio or Young's modulus of elasticity using the acoustical signal data. 
     
     
         5 . The method of  claim 2 , wherein processing the signal data to compute the property value comprises computing shear modulus using the signal data. 
     
     
         6 . The method of  claim 2 , wherein generating the mechanical quality metric includes calculating unconfined compressive strength (UCS) at the one or more locations using the acoustical signal data. 
     
     
         7 . The method of  claim 6 , wherein UCS is calculated as:
   UCS= aE   b   +c      where:
 a, b, and c are empirically obtained coefficients; and 
 E is Young's modulus of elasticity. 
   
     
     
         8 . The method of  claim 2 , wherein generating the mechanical quality metric includes calculating a brittleness metric at the one or more locations based on the acoustical signal data. 
     
     
         9 . The method of  claim 8 , wherein the brittleness metric is calculated as:
     Br= 1 −V   cl (γ iso ) −V   ker  
   where:
 Br is the brittleness metric, 
 V cl  is a relative volume of clay in the material, 
 γ iso  is a relative measure of anisotropy of the material, and 
 V ker  is a relative volume of kerogen in the material; 
   γ iso  is calculated as:
   γ iso =μ iso −μ tor  
 
   where:
 μ iso  is isotropic shear modulus, and 
 μ tor  is torsional shear modulus; and 
   μ tor  is calculated as:
   μ tor   ≅A   ang-RMS /ZFL ang  
 
   where:
 A ang-RMS  is a root mean square value of the acoustical signal data corresponding to an angular acceleration, and 
 ZFL ang  is a zero-frequency level of an angular displacement spectra. 
   
     
     
         10 . The method of  claim 2 , wherein generating the mechanical quality metric includes calculating an anisotropy metric for the one or more locations. 
     
     
         11 . The method of  claim 2  further comprising performing at least one well operation based on the mechanical quality metric at the location, wherein the at least one well operation includes at least one of a drilling operation or a fracturing operation. 
     
     
         12 . A method of evaluating mechanical quality of subterranean formations comprising:
 using a computing processor operatively coupled to a non-transitory computer readable memory, processing sensor signal data captured during drilling of a wellbore through a subterranean formation using a drill bit, wherein processing the sensor signal data computes property values for a mechanical material property at a sequence of locations in the subterranean formation along the wellbore;   processing the property values to generate a mechanical quality metric for each location of the sequence of locations; and   storing the mechanical quality metrics in the non-transitory computer readable memory.   
     
     
         13 . The method of  claim 12  further comprising processing location data from a measurement while drilling (MWD) tool captured during drilling of the wellbore to correlate the property values to the sequence of locations. 
     
     
         14 . The method of  claim 13 , wherein storing the mechanical quality data for the sequence of locations comprises aggregating the mechanical metrics for a consecutive subset of locations of the sequence of locations and storing an aggregated mechanical metric for a range corresponding to the consecutive subset of locations. 
     
     
         15 . The method of  claim 12 , wherein the sensor signal data is acoustical signal data. 
     
     
         16 . The method of  claim 12 , wherein the sensor signal data is provided by one or more sensors of a bottom hole assembly. 
     
     
         17 . The method of  claim 12 , wherein the mechanical material property includes Young's modulus of elasticity (YME) and processing the property values to obtain the mechanical quality metric for each location of the sequence of locations comprises calculating unconfined compressive strength (UCS) using the YME value of the location. 
     
     
         18 . The method of  claim 12 , wherein the mechanical material property includes Young's modulus of elasticity (YME) and processing the at least one set of data values to obtain the mechanical quality data further comprises, for each location of the sequence of locations, calculating a brittleness metric of the location based on YME. 
     
     
         19 . A method of classifying mechanical quality of material in subterranean formations comprising:
 using a computing processor operatively coupled to a non-transitory computer readable memory, computing property values for a mechanical material property at a sequence of locations in the subterranean formation along the wellbore;   processing the property values to generate a mechanical quality metric for each location of the sequence of locations; and   storing the mechanical quality metrics in the non-transitory computer readable memory.   
     
     
         20 . The method of  claim 19 , wherein generating the mechanical quality metric includes calculating unconfined compressive strength (UCS) at each location of the sequence of locations. 
     
     
         21 . The method of  claim 19 , wherein generating the mechanical quality metric includes calculating a brittleness metric at each location of the sequence of locations. 
     
     
         22 . The method of  claim 19 , wherein generating the mechanical quality metric includes calculating an anisotropy metric at each location of the sequence of locations. 
     
     
         23 . The method of  claim 19  further comprising performing at least one well operation based on the mechanical quality metrics. 
     
     
         24 . A tangible, non-transitory, computer-readable media having instructions encoded thereon, the instructions, when executed by a processor, are operable to:
 compute property values for a mechanical material property at a sequence of locations in the subterranean formation along the wellbore;   process the property values to generate a mechanical quality metric for each location of the sequence of locations; and   store the mechanical quality metrics in a non-transitory computer readable memory.   
     
     
         25 . The tangible, non-transitory, computer-readable media of  claim 24 , wherein the property values for the mechanical material property are computed from vibration of a drill bit measured during interaction of the drill bit with the subterranean formation while drilling the wellbore.