Method of predicting rock strength using drilling data for horizontal well placement

Abstract

A system for predicting rock strength for use in horizontal well drilling includes a memory to store computer executable instructions and one or more processors, operatively coupled to the memory, that execute the computer executable instructions to implement a rock strength analyzer configured to determine unconfined compressive strength (UCS) from input parameters, and a well placement module operable to monitor placement of a horizontal well bore in a drilling operation based on the CCS and determined UCS. In certain embodiments, the rock strength analyzer can include a specific energy module for determining specific energy from mechanical and hydraulic specific energy, and a compressive strength module for determining the UCS from confined compressive strength (CCS) as related to specific energy by a mechanical efficiency E m .

The invention claimed is: 
     
         1 . A system for predicting rock strength for use in horizontal well drilling comprising:
 memory to store computer executable instructions; and   one or more processors, operatively coupled to the memory, that execute the computer executable instructions to implement:
 a rock strength analyzer configured to determine unconfined compressive strength (UCS) from input parameters, the rock strength analyzer including:
 a specific energy module for determining specific energy from mechanical and hydraulic specific energy; and 
 a compressive strength module for determining the UCS from confined compressive strength (CCS) as related to specific energy by a mechanical efficiency E m ; and 
 
   a well placement module operable to monitor placement of a horizontal well bore in a drilling operation based on the CCS and determined UCS.   
     
     
         2 . The system of  claim 1 , wherein the input parameters include one or more of:
 a. Downhole-measured drilling parameters including WOB, RPM, and torque   b. Real-time data of ROP, equivalent circulating density and mud flow rate   c. Estimated formation pore pressure   d. Directional survey data and near bit measurement of well inclination, well azimuth and true vertical depth   e. Bit size and bit total nozzle flow area   f. Average drill bit dull grade of bits used to drill same formations   g. Start depth and estimated end depth of each bit in a horizontal section   h. Estimated friction angle for target formation   i. Rock mechanics testing data on core plugs   j. Mechanical efficiency   k. Pressure drop across drill bit   l. Bit impact force   m. Effective WOB with downhole measured WOB   n. Dull grade of a bit at each depth using average dull grade of bits   o. ROP for current bit as if it was new, ROP n , accounting for wear state of the bit using measured ROP and estimated dull grade for each depth   p. Specific energy using the effective WOB, the ROP accounting for bit wear, RPM, torque, pressure drop across the bit, mud flow rate and bit size   q. CCS using the estimated drilling efficiency and the specific energy (calculated)   r. A relationship between CCS and UCS and friction angle based on rock mechanics testing data on core plugs   s. Input data of friction angle.   
     
     
         3 . The system of  claim 1 , further comprising an E m  module to generate the mechanical efficiency E m , the E m  module operable to compare predicted and measured rate of penetration (ROP). 
     
     
         4 . The system of  claim 1 , wherein the compressive strength module includes a CCS calculator for calculating a CCS, and a UCS calculator operable derive the UCS from the calculated CCS. 
     
     
         5 . The system of  claim 4 , wherein the UCS calculator derives the UCS from the calculated CCS based on a CCS/UCS relation from core test data. 
     
     
         6 . The system of  claim 1 , wherein the CCS calculator uses dull grade bit data to calculate CCS. 
     
     
         7 . A computer-implemented method for predicting rock strength for use in horizontal well drilling comprising:
 using drilling and bit data to calculate mechanical specific energy (MSE);   using drilling, mud and bit data to calculate hydraulic specific energy (HSE);   obtaining a specific energy value from the MSE and HSE;   calculating confined compressive strength (CCS) from the specific energy, the CCS related to specific energy by mechanical efficiency E m ;   deriving unconfined compressive strength (UCS) from the CCS; and   monitoring placement of a horizontal well bore in a drilling operation based on the UCS and CCS.   
     
     
         8 . The method of  claim 7 , further comprising determining E m  from offset well analysis. 
     
     
         9 . The method of  claim 7 , wherein calculating CCS comprises using average dull grade of used bits. 
     
     
         10 . The method of  claim 7 , wherein deriving UCS from CCS includes using CCS and UCS relation from core test data. 
     
     
         11 . The method of  claim 7 , further comprising applying one or more input parameters selected from:
 a. Downhole-measured drilling parameters including WOB, RPM, and torque   b. Real-time data of ROP, equivalent circulating density and mud flow rate   c. Estimated formation pore pressure   d. Directional survey data and near bit measurement of well inclination, well azimuth and true vertical depth   e. Bit size and bit total nozzle flow area   f. Average drill bit dull grade of bits used to drill same formations   g. Start depth and estimated end depth of each bit in a horizontal section   h. Estimated friction angle for target formation   i. Rock mechanics testing data on core plugs   j. Mechanical efficiency   k. Pressure drop across drill bit   l. Bit impact force   m. Effective WOB with downhole measured WOB   n. Dull grade of a bit at each depth using average dull grade of bits   o. ROP for current bit as if it was new, ROP n , accounting for wear state of the bit using measured ROP and estimated dull grade for each depth   p. Specific energy using the effective WOB, the ROP accounting for bit wear, RPM, torque, pressure drop across the bit, mud flow rate and bit size   q. CCS using the estimated drilling efficiency and the specific energy (calculated)   r. A relationship between CCS and UCS and friction angle based on rock mechanics testing data on core plugs   s. Input data of friction angle.   
     
     
         12 . A machine-readable storage medium having stored thereon a computer program for predicting rock strength for use in horizontal well drilling, the computer program comprising a routine of set instructions for causing the machine to perform the steps of:
 using drilling and bit data to calculate mechanical specific energy (MSE);   using drilling, mud and bit data to calculate hydraulic specific energy (HSE);   obtaining a specific energy value from the MSE and HSE;   calculating confined compressive strength (CCS) from the specific energy, the CCS related to specific energy by mechanical efficiency E m ;   deriving unconfined compressive strength (UCS) from the CCS; and   monitoring placement of a horizontal well bore in a drilling operation based on the UCS and CCS.   
     
     
         13 . The machine-readable storage medium of  claim 12 , the set of instructions further causing the machine to perform the steps of determining E m  from offset well analysis. 
     
     
         14 . The machine-readable storage medium of  claim 12 , wherein calculating CCS comprises using average dull grade of used bits. 
     
     
         15 . The machine-readable storage medium of  claim 12 , wherein deriving UCS from CCS includes using CCS and UCS relation from core test data. 
     
     
         16 . The machine-readable storage medium of  claim 12 , the set of instructions further causing the machine to perform the steps of applying one or more input parameters selected from:
 a. Downhole-measured drilling parameters including WOB, RPM, and torque   b. Real-time data of ROP, equivalent circulating density and mud flow rate   c. Estimated formation pore pressure   d. Directional survey data and near bit measurement of well inclination, well azimuth and true vertical depth   e. Bit size and bit total nozzle flow area   f. Average drill bit dull grade of bits used to drill same formations   g. Start depth and estimated end depth of each bit in a horizontal section   h. Estimated friction angle for target formation   i. Rock mechanics testing data on core plugs   j. Mechanical efficiency   k. Pressure drop across drill bit   l. Bit impact force   m. Effective WOB with downhole measured WOB   n. Dull grade of a bit at each depth using average dull grade of bits   o. ROP for current bit as if it was new, ROP n , accounting for wear state of the bit using measured ROP and estimated dull grade for each depth   p. Specific energy using the effective WOB, the ROP accounting for bit wear, RPM, torque, pressure drop across the bit, mud flow rate and bit size   q. CCS using the estimated drilling efficiency and the specific energy (calculated)   r. A relationship between CCS and UCS and friction angle based on rock mechanics testing data on core plugs   s. Input data of friction angle.