Steering A Wellbore Using Stratigraphic Misfit Heat Maps

Abstract

Systems and methods for using stratigraphic heat maps to steer a well being drilled. Data from one or more offset wells can be provided to a computer system and used with data from a well being drilled to generate one or more stratigraphic heat maps during the drilling of the subject well. The stratigraphic heat maps can be displayed and used to determine the location of the wellbore relative to one or more geological formations, including one or more target formations or within a target formation. Based on the use of the heat maps and the location of the wellbore relative to a target, the drill plan can be adjusted or updated and/or one or more drilling parameters or operations may be adjusted to drill the wellbore, such as to drill the wellbore to the target or to maximize the length of the wellbore within a target zone.

What is claimed is: 
     
         1 . A computer system for drilling comprising:
 a processor;   a memory coupled to the processor, the memory containing instructions executable by the processor for performing some or all of the following steps:
 identifying a plurality of measured depths along a borehole of a subject well being drilled; 
 obtaining an offset well log with measurements at a plurality of stratigraphic vertical depths of an offset well; 
 computing a misfit value for each of a plurality of pairs of measurements of the subject well at a plurality of measured depths and the offset well at a plurality of stratigraphic vertical depths; 
 generating a stratigraphic misfit heat map representing the misfit value for each of the plurality of pairs of measurements of the subject well; and 
 using the stratigraphic misfit heat map to steer the subject well to a desired stratigraphic vertical depth range. 
   
     
     
         2 . The system of  claim 1 , wherein the misfit value is computed using a stochastic model. 
     
     
         3 . The system according to  claim 1 , wherein the misfit value is computed using a plurality of offset well logs and the system further comprises instructions for:
 selecting a plurality of offset well logs, each having a plurality of measurements at a plurality of true vertical depths;   generating a mapping of true vertical depths against stratigraphic vertical depth, wherein the mapping relates a stratigraphic vertical depth to the corresponding true vertical depths of all of the plurality of offset well logs;   computing a combined misfit value for each of the measurements at measured depths, of the borehole of the subject well, and offset measurements of true vertical depths of all of the plurality of offset well logs;   determining, responsive to the combined misfit value, the stratigraphic vertical depth, of the borehole of the subject well, wherein the stratigraphic vertical depth of the borehole of the subject well corresponds to a minimum cost related to the combined misfit value; and   drilling the borehole of the subject well responsive to the determined stratigraphic vertical depth of the borehole of the subject well to a target stratigraphic vertical depth.   
     
     
         4 . The system according to  claim 1 , wherein the measurements on the subject well log and offset well log include any one or more of gamma ray intensity, azimuthal gamma, resistivity, azimuthal resistivity, density, porosity, rate of progress, mechanical specific energy, rock compressive strength, rate of penetration, differential pressure, and weight on bit. 
     
     
         5 . The system according to  claim 1 , further compromising instructions for displaying the stratigraphic misfit heat map for use in drilling the borehole of the subject well, wherein the displaying comprises displaying the heat map either or both at a drilling site for the subject well or at a remote location from the drilling site. 
     
     
         6 . The system according to  claim 1 , wherein the misfit value is displayed using a combination of measured depths along a borehole of the subject well, stratigraphic vertical depth, of the offset well, a relative stratigraphic vertical depth, true vertical depths of the offset well, and a vertical section on an X axis and a Y axis of the stratigraphic misfit heat map. 
     
     
         7 . The system according to  claim 1 , wherein at least a portion of the stratigraphic misfit heat map displays ancillary data, such as a well plan, a surveyed wellbore position, geological markers, seismic velocities, and/or other geophysical data. 
     
     
         8 . The system according to  claim 1 , wherein a plurality of misfit heat maps for either or both of a plurality of measurement types or a plurality of offset well logs are displayed simultaneously in 3D. 
     
     
         9 . A method for drilling comprising:
 identifying a plurality of measured depths along a borehole of a subject well being drilled;   obtaining an offset well log with measurements at a plurality of stratigraphic vertical depths of an offset well;   computing a misfit value for each of a plurality of pairs of measurements of the subject well at a plurality of measured depths and the offset well at a plurality of stratigraphic vertical depths;   generating a stratigraphic misfit heat map representing the misfit value for each of the plurality of pairs of measurements of the subject well; and   using the stratigraphic misfit heat map to steer the subject well to a desired stratigraphic vertical depth range.   
     
     
         10 . The method of  claim 9 , wherein the misfit value is computed using a stochastic model. 
     
     
         11 . The method according to  claim 9 , wherein the misfit value, is computed using a plurality of offset well logs and the method further comprises:
 selecting a plurality of offset well logs, each having a plurality of measurements at a plurality of true vertical depths;   generating a mapping of true vertical depths against stratigraphic vertical depth, wherein the mapping relates a stratigraphic vertical depth to the corresponding true vertical depths, of all of the plurality of offset well logs;   computing a combined misfit value for each of the measurements at measured depths of the borehole of the subject well, and offset measurements of true vertical depths of all of the plurality of offset well logs;   determining, responsive to the combined misfit value, the stratigraphic vertical depth of the borehole of the subject well, wherein the stratigraphic vertical depth of the borehole of the subject well corresponds to a minimum cost related to the combined misfit value; and   drilling the borehole of the subject well responsive to the determined stratigraphic vertical depth of the borehole of the subject well to a target stratigraphic vertical depth.   
     
     
         12 . The method according to  claim 11 , wherein the plurality of measurements from the plurality of offset well logs are combined into one reference log, and the method further comprising:
 taking a plurality of measurements at measured depths, along the borehole of the subject well;   selecting a plurality of offset well logs with measurements at true vertical depths;   generating a mapping of true vertical depths against stratigraphic vertical depth, which relates a stratigraphic vertical depth to the corresponding true vertical depths of all offset well logs;   combining the measurements of the offset well logs into a common reference well log organized by stratigraphic vertical depth;   computing the Misfit value, MV for each of a plurality of pairs of measurements at subject well measured depths and reference well log organized by stratigraphic vertical depth;   determining, responsive to the computed misfit value, the stratigraphic vertical depth of the subject well by minimizing a cost related to the Misfit value; and   using the determined stratigraphic vertical depth to steer the subject well to a desired stratigraphic depth range.   
     
     
         13 . The method according to  claim 9 , wherein the measurements on the subject well log and offset well log include any one or more of gamma ray intensity, azimuthal gamma, resistivity, azimuthal resistivity, density, porosity, rate of progress, mechanical specific energy, rock compressive strength, rate of penetration, differential pressure, and weight on bit. 
     
     
         14 . The method according to  claim 9 , wherein a stochastic model is used to compute a probability distribution of stratigraphic vertical depth of the subject well at any point along the subject well. 
     
     
         15 . The method according to  claim 9 , wherein the misfit value, MV is displayed using a combination of measured depths, MD SW  along the borehole of the subject well, stratigraphic vertical depth, SVD OW  of the offset well, Relative Stratigraphic Vertical Depth, RSVD, true vertical depths, TVD OW  of the offset well, and Vertical Section on an X axis and a Y axis of the stratigraphic misfit heat map. 
     
     
         16 . The method according to  claim 9 , further comprising displaying the stratigraphic misfit heat map for use in drilling the borehole of the subject well. 
     
     
         17 . The method according to  claim 16 , wherein the heat map displays any one or more of ancillary data, such as a well plan, a surveyed wellbore position, geological markers, seismic velocities, and other geophysical data. 
     
     
         18 . The method according to  claim 16 , wherein multiple misfit heat maps for multiple measurement types or multiple offset well logs are displayed simultaneously. 
     
     
         19 . The method according to  claim 16 , wherein an operator manually interprets paths of a minimal misfit in the heat map to specify a stratigraphic vertical depth, SVD SW  used to direct the drilling of the subject well. 
     
     
         20 . The method according to  claim 9 , wherein a cost function minimization is guided by an operator by specifying stratigraphic control points.