US 6879947 B1
A drill bit is designed to achieve optimum performance in a specified drilling application defined by the drilling system, the formation to be drilled and the configuration of the bore hole. A depth of cut versus predicted torque for
US 6879947 B1
A drill bit is designed to achieve optimum performance in a specified drilling application defined by the drilling system, the formation to be drilled and the configuration of the bore hole. A depth of cut versus predicted torque for a basic bit configuration is evaluated for different configurations of the drill bit. A computer modeling program is used to obtain the predicted torque for the basic bit configuration, and its modifications. Features of the bit design are changed to achieve the lowest predicted torque for an optimum depth of cut. Presenting the computer analysis as depth of cut versus predicted torque for the bit design simplifies the design selection process. The formation being drilled may be evaluated by comparing actual torque with predicted torque for a given rate of penetration. The evaluation can be used to conform the computer model and determine formation properties.
1. A method for improving a drill bit assembly design for drilling a well bore section, comprising:
determining a range of operating parameter values for a drilling system to be employed to drill said well bore section,
determining characteristics of the formation along a trajectory through which said well bore section is to be drilled,
calculating a first rate of penetration through said well bore section for a first drill bit assembly design to be employed with said drilling system for drilling said well bore section, said calculated rate of penetration being determined as a function of calculating with operating parameter values within said range of operating parameter values,
modifying a depth of cut parameter of said first drill bit assembly design to provide a subsequent drill bit assembly design,
calculating a second rate of penetration through said well bore section for said subsequent drill bit assembly design to be employed with said drilling system for drilling said well bore section, said second rate of penetration for said subsequent drill bit assembly being determined as a function of applying operating parameters within said range of operating parameters, and
selecting a selected drill bit assembly design from said first and subsequent drill bit assembly designs having the calculated rate of penetration.
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determining a depth of cut verses predicted torque relationship for said selected drill bit assembly design using said computer modeling program, and
drilling said well bore section with a drilling bit assembly having said selected drill bit assembly design.
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17. A method for matching a drilling bit assembly to a specific drilling application, comprising:
determining a range of system operating parameters for a drilling system to be employed to drill a well bore section through a selected medium,
selecting a basic drilling bit assembly design having a first set of bit characteristics,
using a computer modeling program to determine a first set of torque characteristics of a bit of the basic drilling bit assembly design going through the selected medium, said computer modeling program evaluating reaction torque in a bit of the basic drilling bit assembly design as a function of the characteristics of the selected medium, the weight on a bit of the basic drilling bit assembly design, the rate of rotation of a bit of the basic drilling bit assembly design and/or the rate of penetration of a bit of the basic drilling bit assembly design through the selected medium,
modifying a depth of cut characteristic of the basic drilling bit assembly design to produce a modified drilling bit assembly design with a greater depth of cut than the basic drilling bit assembly design, said modified bit assembly design being operable within said range of system operating parameters for said drilling system,
using said computer modeling program to determine a second set of torque characteristics of the modified bit assembly design,
expressing representations of depth of cut verses torque values for said basic drilling bit assembly design and said modified drilling bit assembly design, and
selecting a drilling bit assembly design using information from the expression of the depth of cut verses torque values.
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