ρ

c
-
d

Eq
.

2

where ρ_c-dis the downhole compressible density, ρ_c-sis the surface compressible density, and Q_c-sis the surface compressible flow component. The fractional flow model 258 may determine the surface compressible flow component Q_c-sthrough direct measurement prior to mixing and/or through inference and/or calculation based on conditions at mixing.

The fractional flow model 258 may calculate a downhole compressible fraction f_c-dof the compressible flow component based on Eq. 3:

$\begin{matrix} f_{c - d} = \frac{Q_{c - d}}{Q_{ic} + Q_{c - d}} & Eq . 3 \end{matrix}$

where Q_icis the incompressible flow component. Using the downhole flow fraction, the fractional flow model 258 may calculate the downhole composite flow rate Q_compbased on Eq. 4:

$\begin{matrix} Q_{comp} = \frac{Q_{ic}}{1 - f_{c - d}} & Eq . 4 \end{matrix}$

The fractional flow model 258 may further generate a drilling fluid composite density ρ_compfor the downhole composite flow based on Eq. 5:

$\begin{matrix} ρ_{comp} = f_{c - d} * ρ_{c - d} + (1 - f_{c - d}) * ρ_{ic} & Eq . 4 \end{matrix}$

where ρ_icis the incompressible fluid density.

In accordance with at least one embodiment of the present disclosure, a motor performance model 260 may use the drilling fluid composite density and the composite flow rate to calculate or estimate the downhole motor torque and RPM. For example, the motor performance model 260 may utilize the performance diagrams for the downhole motor to determine the motor torque and the RPM. As discussed above, the downhole composite flow rate and the downhole composite density may be different than the surface flow rate and surface density. In this manner, the motor performance model 260 may calculate or determine motor torque and RPM that are representative of the actual conditions at the downhole motor.

A drilling fluid controller 262 may determine whether the motor torque and RPM are within a threshold range based on the properties of the downhole motor and/or the operating parameters of the downhole tools associated with, powered by, or receiving power indirectly from the downhole motor. If the drilling fluid controller 262 determines that the motor torque and RPM are outside of the threshold range, the fluid composition manager 242 may adjust the properties of the drilling fluid. For example, the fluid composition manager 242 may cause the compressible fluid controller 244 and/or the incompressible fluid controller 246 to adjust the composition of the drilling fluid. In some examples, the fluid composition manager 242 may cause the fluid pumps 248 to increase the flow rate of the compressible portion and/or the incompressible portion.

As a specific, non-limiting example, when the drilling fluid controller 262 determines that the motor torque is above a high torque threshold, the fluid composition manager 242 may cause the fluid pumps 248 to reduce the flow rate of the compressible portion and/or the incompressible portion. In some examples, the fluid composition manager 242 may cause the compressible fluid controller 244 and the incompressible fluid controller 246 to decrease the amount of the compressible fluid mixed with the incompressible fluid. These actions may reduce the motor torque.

As a specific, non-limiting example, when the drilling fluid controller 262 determines that the RPM is above a high RPM threshold, the fluid composition manager 242 may cause the fluid pumps 248 to reduce the flow rate of the compressible portion and/or the incompressible portion. In some examples, the fluid composition manager 242 may cause the compressible fluid controller 244 and the incompressible fluid controller 246 to decrease the amount of the compressible fluid mixed with the incompressible fluid. These actions may reduce the RPM.

As a specific, non-limiting example, when the drilling fluid controller 262 determines that the motor torque is below a low torque threshold, the fluid composition manager 242 may cause the fluid pumps 248 to increase the flow rate of the compressible portion and/or the incompressible portion. In some examples, the fluid composition manager 242 may cause the compressible fluid controller 244 and the incompressible fluid controller 246 to increase the amount of the compressible fluid mixed with the incompressible fluid. These actions may increase the motor torque.

As a specific, non-limiting example, when the drilling fluid controller 262 determines that the RPM is below a low RPM threshold, the fluid composition manager 242 may cause the fluid pumps 248 to increase the flow rate of the compressible portion and/or the incompressible portion. In some examples, the fluid composition manager 242 may cause the compressible fluid controller 244 and the incompressible fluid controller 246 to increase the amount of the compressible fluid mixed with the incompressible fluid. These actions may increase the RPM.

The drilling fluid controller 262 may identify when the motor torque is within a torque threshold range defined by the low torque threshold and the high torque threshold. In some embodiments, the drilling fluid controller 262 may identify when the RPM is within an RPM threshold range defined by the low RPM threshold and the high RPM threshold.

FIG. 3-6, the corresponding text, and the examples provide a number of different methods, systems, devices, and computer-readable media of the downhole motor control system 240. In addition to the foregoing, one or more embodiments can also be described in terms of flowcharts comprising acts for accomplishing a particular result, as shown in FIG. 3-6. FIG. 3-6 may be performed with more or fewer acts. Further, the acts may be performed in differing orders. Additionally, the acts described herein may be repeated or performed in parallel with one another or parallel with different instances of the same or similar acts.

As mentioned, FIG. 3 illustrates a flowchart of a series of acts or a method 364 for identifying an output of a downhole motor, according to at least one embodiment of the present disclosure. While FIG. 3 illustrates acts according to one embodiment, alternative embodiments may omit, add to, reorder, and/or modify any of the acts shown in FIG. 3. The acts of FIG. 3 can be performed as part of a method. Alternatively, a computer-readable medium can comprise instructions that, when executed by one or more processors, cause a computing device to perform the acts of FIG. 3. In some embodiments, a system can perform the acts of FIG. 3.

A downhole motor control system may monitor the downhole pressure and temperature of a drilling fluid at 366. For example, a BHA, measuring while drilling (MWD), logging while drilling (LWD), or other downhole control system may measure the downhole pressure and temperature of the drilling fluid. The BHA may transmit the downhole pressure and temperature to the surface. For example, in a CT or wireline drilling environment, the CT tubing or wireline may include an electrical connection with the surface, and the downhole pressure and temperature may be transmitted to the surface over the electrical connection.

In some embodiments, using the downhole pressure and temperature, the downhole motor control system may calculate the downhole compressible density of the compressible portion of the drilling fluid at 368. Using the downhole compressible density, the surface compressible density, and the surface compressible flow component of the drilling fluid, the downhole motor control system may calculate the downhole compressible flow component of the drilling fluid. Using the downhole compressible flow component, the downhole motor control system may calculate the downhole compressible drilling fluid fraction at 370. This may then be used to calculate the composite flow rate of the drilling fluid at the downhole motor at 372. The downhole motor control system may calculate other downhole properties, including the composite density, which may be used to determine the motor torque and RPM of the downhole motor at 374.

In accordance with at least one embodiment of the present disclosure, the downhole motor control system may determine 376 whether the torque and RPM are within a threshold range. If the torque and RPM are within the threshold range, then the downhole motor control system may continue to monitor the downhole pressure and temperature and calculate the composite flow rate to determine the motor torque and RPM.

Specifically, the downhole motor control system may measure a second downhole temperature and a second downhole pressure at a second time after the first time. Using the second downhole pressure and the second downhole temperature, the downhole motor control system may calculate a second downhole compressible density of the compressible portion of the drilling fluid. Using the second downhole compressible density, the surface compressible density (which may be a second surface compressible density if it changed), and the surface compressible flow component (which may be a second surface compressible flow component if it changed) of the drilling fluid, the downhole motor control system may calculate a second downhole compressible flow component of the drilling fluid. Using the second downhole compressible flow component, the downhole motor control system may calculate a second downhole compressible drilling fluid fraction. This may then be used to calculate a second composite flow rate of the drilling fluid at the downhole motor. The downhole motor control system may calculate other downhole properties, including a second composite density, which may be used to determine a second motor torque and a second RPM of the downhole motor. The downhole motor control system may then determine 376 whether the second motor torque and the second RPM are within the threshold range. If they are within the threshold range, then the downhole motor control system may continue to monitor and calculate new values.

If the motor torque and/or RPM are outside of the threshold range, the downhole motor control system may adjust one or more drilling properties of the drilling fluid at the surface location at 378. For example, the downhole motor control system may adjust the fluid flow rate of the incompressible flow component. In some examples, the downhole motor control system may adjust the fluid flow rate or mass flow rate of the surface compressible flow component. In some examples, the downhole motor control system may adjust the pressure of the surface compressible portion of the fluid flow.

As mentioned, FIG. 4 illustrates a flowchart of a series of acts or a method 400 for identifying an output of a downhole motor, according to at least one embodiment of the present disclosure. While FIG. 4 illustrates acts according to one embodiment, alternative embodiments may omit, add to, reorder, and/or modify any of the acts shown in FIG. 4. The acts of FIG. 4 can be performed as part of a method. Alternatively, a computer-readable medium can comprise instructions that, when executed by one or more processors, cause a computing device to perform the acts of FIG. 4. In some embodiments, a system can perform the acts of FIG. 4.

The downhole motor control system 240 or an operator may mix a drilling fluid at 401. To mix the drilling fluid, the downhole motor control system 240 may add an incompressible fluid at 402 and add a compressible fluid at 403. The incompressible fluid may be added with an incompressible flow component, or an incompressible portion flow rate, at 404. Because the incompressible fluid is incompressible, the incompressible flow component may be the same at the surface location as downhole. The compressible fluid may be added with a surface compressible flow component, or a compressible surface flow rate, at 405.

Using the properties of the drilling fluid, a conversion model 406 may convert measured downhole pressure and temperature 407 to a downhole compressible flow component, or a downhole flow rate of the compressible portion 408. As discussed herein, the conversion model 406 may include any model, such as the status manager 256 and/or fractional flow model 258 of FIG. 2.

The downhole motor control system 240 may determine, using the incompressible flow component and the downhole compressible flow component, a composite downhole flow rate 409 of the drilling fluid. A motor performance model 410 may utilize the composite downhole flow rate, and other associated parameters as discussed herein, to determine an output torque 411 and an output RPM 412 of the downhole motor.

As mentioned, FIG. 5 illustrates a flowchart of a series of acts or a method 500 for identifying an output of a downhole motor, according to at least one embodiment of the present disclosure. While FIG. 5 illustrates acts according to one embodiment, alternative embodiments may omit, add to, reorder, and/or modify any of the acts shown in FIG. 5. The acts of FIG. 5 can be performed as part of a method. Alternatively, a computer-readable medium can comprise instructions that, when executed by one or more processors, cause a computing device to perform the acts of FIG. 5. In some embodiments, a system can perform the acts of FIG. 5.

The downhole motor control system may identify a downhole compressible density of a drilling fluid using a downhole temperature and a downhole pressure of the drilling fluid at 501. As discussed herein, the drilling fluid includes an incompressible portion and a compressible portion. The drilling fluid flows downhole hole with a compressible flow component and an incompressible flow component.

The downhole motor control system may determine the downhole compressible flow component using the downhole compressible density, a surface compressible density of the compressible portion at a surface location, and a surface compressible flow component of the compressible portion at the surface location at 502. The downhole motor control system may identify a downhole compressible volume fraction of the drilling fluid based on the downhole compressible flow component and the incompressible flow component at 503. The downhole motor control system may generate a composite flow rate of the drilling fluid based on the incompressible flow component and the downhole compressible volume fraction at 504.

As discussed in further detail herein, the downhole motor control system may further generate a drilling fluid composite density based on the downhole compressible density, an incompressible density of the incompressible component, and the downhole compressible volume fraction. The downhole motor control system may use the composite flow rate and the drilling fluid composite density to generate a downhole motor torque and rotational rate (e.g., RPM). The downhole motor control system may, based on the determined downhole motor torque and rotational rate, adjust the properties of the drilling fluid, as discussed in further detail herein.

As mentioned, FIG. 6 illustrates a flowchart of a series of acts or a method 600 for identifying an output of a downhole motor, according to at least one embodiment of the present disclosure. While FIG. 6 illustrates acts according to one embodiment, alternative embodiments may omit, add to, reorder, and/or modify any of the acts shown in FIG. 6. The acts of FIG. 6 can be performed as part of a method. Alternatively, a computer-readable medium can comprise instructions that, when executed by one or more processors, cause a computing device to perform the acts of FIG. 6. In some embodiments, a system can perform the acts of FIG. 6.

The downhole motor control system may cause surface drilling equipment or surface pumping equipment to, at a surface location, combine an incompressible fluid and a compressible fluid at 601. Combining, or causing the surface pumping equipment to combine, the incompressible fluid and the compressible fluid results in a drilling fluid having an incompressible portion and a compressible portion. The compressible portion has a surface compressible density and a surface compressible flow component.

The downhole motor control system may measure, or cause downhole temperature sensors to measure, a downhole temperature and a downhole pressure of the drilling fluid at 602. The downhole motor control system may calculate a downhole compressible fraction of the drilling fluid using the downhole temperature and the downhole pressure at 603. The downhole motor control system may determine a motor torque and a rotational rate of a downhole motor using the downhole compressible fraction of the drilling fluid at 604. The downhole motor control system may, when the motor torque or the rotational rate are outside of a threshold range, adjust the incompressible portion or the compressible portion of the drilling fluid at 605. In some embodiments, when the motor torque and the rotational rate are within the threshold range, the downhole motor control system may maintain the incompressible portion and the compressible portion, or may maintain the relative ratios and flow components of the drilling fluid.

In accordance with at least one embodiment of the present disclosure, the downhole motor control system may be at least partially downhole, or at least a portion of the measurements and calculations may occur downhole at the BHA or at the downhole motor. The BHA may transmit the information collected and/or measured to the surface. For example, the BHA may transmit the measured downhole temperature and the measured downhole pressure to the surface. The BHA may transmit information to the surface in any manner. For example, the BHA may transmit the information to the surface using a wired connection, electromagnetic communication, mud pulse telemetry, any other communication mechanism, and combinations thereof.

In some embodiments, the BHA may communicate information to the surface in real-time. For example, the BHA may transmit information to the surface as it is measured, or after being cached in downhole memory for a brief period. Real-time communication and calculation may be communication or calculations that occur after a delay period of less than 1 s, less than 0.5 s, less than 0.1 s, less than 0.01 s, and any value therebetween.

As discussed herein, the determination of motor torque and rotational rate may be performed in a loop, or may be continuously monitored. For example, the downhole temperature may be a first downhole temperature, the downhole pressure may be a first downhole pressure, and the downhole motor control system may measure a second downhole temperature and a second downhole pressure. The downhole motor control system may calculate a second downhole compressible fraction of the drilling fluid using the second downhole temperature and the second downhole pressure. The downhole motor control system may determine a second motor torque and a second rotational rate of the downhole motor using the second downhole compressible fraction of the drilling fluid. The downhole motor control system may then determine whether the second motor torque and the second rotational rate are within the threshold range, and either maintain or adjust the incompressible portion and the compressible portion accordingly.