Motors and Rotary Steerable Units

class: bottom, left, inverse, title-slide

.title[
# Motors and Rotary Steerable Units
]
.author[
### Sam Stehno
]
.date[
### 06/16/2022
]

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# Power Sections

<ul>
 <li>The characteristics of a performance drilling motor are a function of the design of the rotor and stator geometry </li> 
 <li>Typically, the 1/2 or 2/3 ratio motors are best for straight drilling due to their high speed </li> 
 <li>The high 7/8 or above motors are usually good for directional drilling because of the better torque control they provide </li>

???
Speed and torque have an important relationship to consider when evaluating motor efficiency. ______
The number of lobes of the rotor and stator and their pitch angle greatly affect the available torque and rotational speed of the drill.______
Typically, the higher the ratio of rotor to stator lobes, as denoted by a r/s fraction, the lower the speed of drilling and higher torque output._______
Baker Hughes develops their own pre-contoured stators for their motors._______

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# Bearing Assemblies

<ul>
 <li>They support the axial load (or weight on bit) </li> 
 <li>They centralize and support side loading on the motor's driveshaft </li> 
 <li>All are fluid-lubricated and optimized for specific drilling applications </li> 
 <li>The ball bearing assembly and the diamond bearing assembly are the two main types used </li>
</ul>

???
*in a positive displacement drilling motor ____.
Ball bearings are typically meant for less fast motors where the main goal is driving more torque into the bit, which they are suited for because they are built with the capability of a step-change in torque capacity to accomodate whatever is necessary for the motor to perform at it's peak efficiency. The essential idea of ball bearings is that they reduce friction by rolling with their smooth surfaces to effectively bear the load so the motor can spin smoothly. ____
Diamonds, on the other hand, have the advantage of being extremely tough while also causing low friction, so they allow the application of drilling with high-speed motors or a significant increase in weight on bit with low speed motors.

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# Rotary Steerable Systems

<ul>
 <li>The downlink commander (considered the brain) of the bit enables bi-directional communication between surface systems and downhole tools </li> 
 <li>We use an on/off pad cycle with continuous proportional steering to more accurately drill the path than a fixed-tilt BHA </li> 
 <li>The pads/ribs are automatically adjusted by the power of the hydraulic system, which results in continuous rotation, also improving hole cleaning </li> 
 <li>AutoTrak stators are built flexible to reduce stiffness in the BHA </li>
</ul>

???
One of the most relevant measurements that improve geo-steering capabilities, for example, is the system's ability to relay near-bit azimuthal gamma ray readings to the surface and the steering system._____
This system helps to maximize the rate of penetration, extend horizontal sections, and minimize torque and drag limitations.______
This system works because each rib/pad had its own hydraulic motor that powers it outward when it is the one needed to push the drill in the right direction. This also allows for the people analyzing the drill to understand what each rib was doing at every moment better.____
Another benefit of this system is that it makes casing and cementing the hole easier, since the hole gets drilled with as little deviation from its target path as possible.

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# AKO Angle Control

<ul>
 <li>AKO steering system have a basic three-point geometry approach:</li>
 <ul>
 <li>Bit Gauge </li>
 <li>Bearing House Stabilizer </li>
 <li>String Stabilizer </li> 
 </ul>
 <li>AKO systems are implemented where a well is planned to kickoff from a vertical or to initiate a sidetrack </li> 
 <li>They can also maintain constant trajectories by being programmed to their lower settings, while decreasing stress on the tool and bit </li> 
 <li>The main types are the half-shell AKO and the double-pin AKO </li>

???
The half shell is the primary type of AKO adjuster used.____
The way it works is that it has one tapered thread connection with increased wall thickness. This allows a high bending load limit and the attached wear ring and adjusting rings gain a certain amount of leverage that causes the drill from that point down to rotate with a larger radius that is controllable by adjusting the AKI settings.

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# What is in Our Control?

???
Here we just have an example chart from the motors manual comparing the expected performance of motors of the same size but with two different rotor/stator configurations. As we can see, the one with the greater ratio (7/8), regardless of the fact that it has the same flow rate as the other, operates at a higher rotational speed because of the increased amount of rotor lobes that the fluid is flowing through. Also, it shows an increase in differential pressure, torque, and power output in the motor with a higher ratio. This is all very important because it shows the significance of being able to adjust the motor design as necessary, depending on the given circumstances. Below is also a graph of their hypothetical performances.

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# Motor Efficiency

???
Here is just the equation for input and output horsepower of a motor. The input horsepower is defined by the product of the differential pressure (psi) and the flow rate (gpm) divided 1714, while the output horsepower is defined as the product of the operating torque(ft-lbs) and the speed (rpm) of the motor divided by 5252. These are important metrics to know about a drill's performance, and the overal performance drilling motor efficiency is found by taking the ratio of output horsepower to input horsepower.

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