Heating a formation of the earth while drilling a wellbore

1. A method comprising:

while drilling a wellbore in a target zone of a formation of the Earth with a drilling assembly, the wellbore comprising a drilling mud:

receiving, by a controller and from a first sensor, a first signal representing a first temperature of the drilling mud at a drilling end of the drilling assembly, the first temperature of the drilling mud at a depth in the wellbore;

after receiving the first signal, heating, by a heat source mounted to the drilling assembly, a portion of the formation proximal to the depth, to a temperature greater than a formation temperature as the drilling assembly drills through the formation of the Earth;

simultaneously while heating the portion of the formation proximal to the depth while the drilling assembly drills through the formation of the Earth and the drilling mud receiving heat back from the portion of the formation by a flow of the drilling mud, receiving, by the controller from a second sensor, the second sensor farther from the drilling end of the drilling assembly than the first sensor, a second signal representing a second temperature of the drilling mud, the heat source positioned in the drilling assembly between the first sensor and the second sensor;

comparing, by the controller, a difference between of the first temperature of the drilling mud and the second temperature of the drilling mud to a threshold drilling mud temperature difference;

based on a result of the comparison, determining when the difference between the first temperature of the drilling mud and the second temperature of the drilling mud is less than the threshold drilling mud temperature difference, indicating that the drilling assembly is in an oil-bearing portion of the formation and the target zone is the oil-bearing portion of the formation; and

based on determining when the difference between the first temperature of the drilling mud and the second temperature of the drilling mud is less than the threshold drilling mud temperature difference, controlling, by the controller, the drilling assembly in the formation, wherein controlling the drilling assembly in the formation comprises maintaining the drilling assembly in the target zone.

2. The method of claim 1 , wherein receiving, by the controller and from the first sensor, the first signal representing the first temperature of the drilling mud at the depth comprises sensing, by the first sensor, the first temperature of a portion of the drilling mud in the wellbore proximal to the formation at the depth in the wellbore, and

receiving, by the controller and from the second sensor, the second signal representing the second temperature of the drilling mud comprises sensing, by the second sensor, the second temperature of the portion of the drilling mud in the wellbore proximal to the formation.

3. The method of claim 1 , further comprising:

based on the result of the comparison, determining when the difference between the first temperature of the drilling mud and the second temperature of the drilling mud is greater than the threshold drilling mud temperature difference , indicating that the drilling assembly is in a water-bearing portion of the formation and the target zone is the oil-bearing portion of the formation; and

based on determining when the difference between the value of the first temperature of the drilling mud and the second temperature of the drilling mud is greater than the threshold drilling mud temperature difference , controlling, by the controller, the drilling assembly in the formation, wherein controlling the drilling assembly in the formation comprises steering the drilling assembly from the water-bearing portion of the formation to oil-bearing portion of the formation.

4. The method of claim 3 , wherein steering the drilling assembly comprises adjusting at least one of a weight on bit, a revolution per minute, a tool face orientation, a drilling direction, a drilling azimuth, or a drilling mud flow rate.

5. The method of claim 1 , wherein the heat source is a plurality of magnetrons, and wherein heating the formation comprises:

energizing the plurality of magnetrons; and

transmitting a plurality of microwaves from each of the plurality of magnetrons to the formation.

6. The method of claim 5 , wherein heating the formation further comprises transmitting the plurality of microwaves from each of the plurality of magnetrons in an axis parallel to a longitudinal axis of the drilling assembly.

7. The method of claim 5 , wherein the drilling assembly comprises a sleeve, the sleeve mechanically coupled to a downhole conveyor by a bearing assembly, the sleeve rotatably isolated from a rotation of the drilling assembly, the plurality of magnetrons positioned on the sleeve, transmitting the plurality of microwaves from each of the plurality of magnetrons in an axis parallel to a longitudinal axis of the drilling assembly comprises:

rotating the drilling assembly; and

maintaining, by the bearing assembly, the axis of the plurality of magnetrons parallel to the longitudinal axis of the drilling assembly.

8. The method of claim 7 , wherein the sleeve is electrically coupled to a power source by an electrical slip ring, transmitting the plurality of microwaves from each of the plurality of magnetrons in the axis parallel to the longitudinal axis of the drilling assembly comprises:

flowing electricity from the power source;

receiving electricity at the electrical slip ring;

transferring electricity through the electrical slip ring; and

flowing electricity to the plurality of magnetrons.

9. An assembly comprising:

a sleeve configured to couple to a drilling assembly and disposed in a wellbore comprising a drilling mud;

a heat source positioned in the sleeve, the heat source configured to heat a portion of a formation of the Earth;

a first sensor positioned at a first end of the sleeve, the first sensor configured to sense a first condition of the drilling mud at a depth and transmit a signal representing a value of the first condition of the drilling mud at the depth before the heat source heats the portion of the formation of the Earth, wherein the first sensor is a first temperature sensor and the first condition is a first temperature of the drilling mud;

a second sensor positioned at a second end of the sleeve, the second sensor configured to sense a second condition of the drilling mud responsive to the drilling mud receiving heat back from the portion of the formation by a flow of the drilling mud after the heat source heats the portion of the formation and transmit a signal representing a value of the second condition of the drilling mud, wherein the second sensor is a second temperature sensor and the second condition is a second temperature of the drilling mud; and

a controller configured to:

receive the signal representing the value of the first condition;

receive the signal representing the value of the second condition;

compare a difference between the value of the first condition and the value of the second condition to a threshold difference value, wherein the threshold difference value is a threshold drilling mud temperature difference value; and

based on a result of the comparison, generate a command signal to control the drilling assembly, wherein in response to the difference between the value of the first temperature of the drilling mud and the value of the second temperature of the drilling mud less than the threshold drilling mud temperature difference value, indicating the drilling assembly is in an oil-bearing portion of the formation and a target zone is the oil-bearing portion of the formation, the command signal to control the drilling assembly maintains the drilling assembly in the target zone.

10. The assembly of claim 9 , further comprising:

a first connection mechanically coupled to the sleeve, the first connection configured to mechanically couple to a downhole conveyor; and

a second connection mechanically coupled to the sleeve, the second connection configured to mechanically couple to a downhole tool.

11. The assembly of claim 9 , further comprising a bearing assembly positioned within the sleeve, the bearing assembly configured to rotatably isolate the sleeve from a rotation of a downhole conveyor.

12. The assembly of claim 9 , further comprising a plurality of bars mechanically coupled to an outside surface of the sleeve, the plurality of bars configured to slideably engage an inner surface of the wellbore.

13. The assembly of claim 9 , further comprising an electrical slip ring positioned within the sleeve, the electrical slip ring configured to transfer electricity from a power source to the heat source.

14. The assembly of claim 9 , wherein the heat source comprises a plurality of magnetrons.

15. The assembly of claim 14 , wherein a portion of the plurality of magnetrons are arranged linearly relative to a longitudinal axis of the sleeve.

16. The assembly of claim 9 , wherein the controller is further configured to:

responsive to the comparison, determine when the difference between the value of the first temperature of the drilling mud and the value of the second temperature of the drilling mud is greater than the threshold drilling mud temperature difference value, indicating the drilling assembly is in a water-bearing portion of the formation and the target zone is the oil-bearing portion of the formation; and

responsive to determining when the difference between the value of the first temperature of the drilling mud and the value of the second temperature of the drilling mud is greater than the threshold drilling mud temperature difference value, steer the drilling assembly from the water-bearing portion of the formation to the oil-bearing portion of the formation.