Apparatus and method for drilling boreholes

A mud motor for use in drilling a borehole, comprising:

• a) a stator having a helically contoured inner surface;
• b) a rotor having a helically contourer outer surface rotatably disposed in the stator to rotate along a common axis of the stator and motor, said rotor cooperating with the stator when a pressurized fluid is passed between the stator and the rotor to generate rotary force;
• and
• c) at least one temperature sensor within the mud motor for measuring the temperature of a mud motor element for determining an operating parameter of the mud motor during the drilling of the borehole.

A drilling tool assembly for use in drilling a borehole, comprising:

• (a) a drill bit;
• (b) a mud motor coupled to the drill for rotating the drill bit, said mud motor having:
• (i) a stator having a helically contoured inner surface,
• (ii) a rotor having a helically contoured outer surface rotatably disposed in the stator to rotate along a common axis of the stator and motor, said rotor cooperating with the stator when a pressurized fluid is passed through the mud motor to generate rotary force,
• (iii) a sensor within the mud motor for providing signals representative of the pressure differential across the mud motor when the pressurized fluid passes through the mud motor;
• and
• (c) a measurement-while-drilling (MWD) device for determining a formation parameter during drilling of the borehole.

A drilling tool assembly for use in drilling a borehole, comprising:

• (a) a mud motor having a stator having a helically contoured inner surface, a rotor having a helically contoured outer surface rotatably disposed in the stator, said rotor cooperating with the stator when a pressurized fluid is passed through the mud motor to generate rotary force, and a sensor within the mud motor for providing signals representative of the pressure differential across the rotor when the pressurized fluid passes through the mud motor at a known fluid flow rate;
• (b) a control circuit for receiving and processing signals from the sensor;
• and
• (d) a telemetry system for receiving signals from the control circuit and for transmitting such received signals to other devices.

A system for drilling boreholes, comprising:

• (a) a drill string having a drill bit at a bottom end;
• (b) a mud motor coupled to the drill bit, said mud motor rotating the drill bit when a pressurized fluid is passed through the mud motor, said mud motor developing pressure differential across the mud motor when the mud motor is rotating the drill bit, said mud motor including a sensor within the mud motor for providing signals representative of the pressure differential across the mud motor;
• (c) a drawworks coupled to the drill string for controlling weight on bit (WOB) during the drilling of the boreholes;
• and
• (d) a surface control system for receiving signals representative of the differential pressure across the motor and in response thereto for controlling the WOB during drilling of the boreholes for minimizing mud motor wear.

A method of drilling a borehole utilizing a drill string having a drill bit at a bottom end and a mud motor coupled to the drill bit for rotating the drill bit when a pressurized fluid is passed through the mud motor, said method comprising the steps of:

• (a) placing the drill string in the wellbore with the drill bit at the borehole bottom;
• (b) passing the pressurized fluid through the mud motor at a known fluid flow rate to rotate the drill bit;
• (c) measuring differential pressure across the mud motor with a sensor in the mud motor;
• and
• (d) controlling the drilling of the borehole by controlling weight on the drill bit so as to maintain the differential pressure within a predetermined range of values.

A method of determining the wear condition of a first mud motor during drilling of a borehole by a drill string having a drill bit at a bottom end that is rotated by the first mud motor when a pressurized fluid is passed through the first mud motor, said first mud motor developing pressure differential across the first mud motor when the pressurized fluid passes therethrough, said method comprising:

• (a) placing the drill string in the borehole;
• (b) drilling the borehole for a period of time at an known value of weight on the drill bit (WOB);
• (c) reducing WOB to a relatively small value compared to the known WOB;
• (c) measuring differential pressure across the first mud motor at the reduced WOB and at a known fluid flow rate through the first mud motor;
• and
• (d) comparing the measured differential pressure with a differential pressure measurement made at the known fluid flow rate of a second mud motor to determine the wear condition of the mud motor.

A drilling assembly for use in drilling a wellbore, comprising:

• (a) a drilling motor for generating rotary force in response to the flow of a pressurized fluid through the drilling motor;
• and
• (b) a bearing assembly having:
• (i) a housing;
• (ii) a drive shaft rotatably disposed in the housing, said drive shaft adapted to be rotated by the drilling motor;
• (iii) at least one radial bearing between the drive shaft and the housing for providing lateral restraint to the drive shaft;
• (iv) a thrust bearing in the bearing assembly for restricting axial movement of the drive shaft during drilling of the wellbore;
• and
• (v) at least one sensor in the bearing assembly that is selected from a group of sensors comprising a radial displacement sensor for determining the radial displacement of the drive shaft, an axial displacement sensor for determining the axial displacement of the drill shaft, at least one temperature sensor for determining the temperature of the bearing assembly at a selected location in the bearing assembly, and a pressure sensor for determining weight on bit during drilling of the wellbore with the drilling assembly.

A drilling assembly for use in drilling of a wellbore, comprising:

• (a) a drilling motor for generating rotary force in response to the flow of a pressurized fluid through the drilling motor;
• and
• (b) a bearing assembly comprising:
• (i) a housing;
• (ii) a drive shaft rotatably disposed in said housing, said drive shaft adapted to be rotated by the drilling motor, and wherein said drive shaft and said housing defining an inclining gap therebetween;
• and
• (c) a sensor associated with the inclining gap for determining radial and axial displacements of the drill shaft relative to the housing during drilling of the wellbore.

A bearing assembly for use in drilling of a wellbore, comprising:

• (a) a housing;
• (b) a drive shaft rotatably disposed in the housing for rotating a drill bit during drilling of the wellbore;
• (c) at least one radial bearing between the drive shaft and the housing for providing lateral restraint to the drive shaft;
• (d) a thrust bearing in the bearing assembly for restricting axial movement of the drive shaft during drilling of the wellbore;
• (e) a source of lubricating fluid for providing the lubricating fluid to the at least one radial bearing and the thrust bearing to lubricate such bearings during drilling of the wellbore;
• and
• (f) a sensor disposed within or adjacent to said housing which is associated with the source of the lubricating fluid for providing a measurement for determining at least one of the (i) presence of a leak between the source and the bearing, (b) wear condition of the at least one radial bearing, or the remaining life of the at least one radial bearing.