Mud Motor Build Rate Calculator – Directional Drilling Tools
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Calculated Yield
Geometric Build Rate
0.00° / 100ft
Theoretical Dogleg Severity (DLS) based on geometry.
Total Angle Change
0.00°
Total degrees gained over the slide distance.
Radius of Curvature
0 ft
The turning radius of the wellbore arc.
Mud Motor Build Rate Calculator
This calculator is designed for directional drillers (DDs) and drilling engineers to estimate the theoretical geometric build rate (GBR) of a steerable mud motor assembly. By inputting the bend angle of the motor housing and the distance from the bit to the top stabilizer, you can calculate the potential dogleg severity (DLS) and predict the wellbore trajectory during sliding operations.
How to Calculate Mud Motor Yield
The build rate of a Positive Displacement Motor (PDM) is primarily determined by the three-point geometry formed by the bit, the bend in the housing, and the first touch-point above the bend (usually the top stabilizer or kick pad). While formation characteristics significantly impact the actual yield, the geometric yield provides the theoretical maximum.
The standard field approximation formula used in this calculator is:
GBR = (200 × Bend Angle) / L
Where:
- GBR: Geometric Build Rate (Degrees per 100 feet).
- Bend Angle: The setting of the adjustable bend housing (e.g., 1.5°, 1.83°).
- L: The length from the bit face to the top stabilizer (feet).
Understanding the Inputs
| Parameter |
Description |
Typical Values |
| Bend Setting |
The angle deviation set on the motor housing. Higher angles create more aggressive turns (higher DLS) but increase stress on the tool. |
1.15° to 3.0° |
| Bit to Stabilizer |
The geometric length that dictates the pivot point of the assembly. A shorter distance generally results in a higher build rate for the same bend angle. |
15 ft to 28 ft |
| Slide Distance |
The specific interval length drilled without rotating the drill string (sliding). This calculates the total degrees of inclination or azimuth change achieved. |
10 ft to 90 ft (one stand) |
Factors Affecting Actual Build Rate
While the calculator provides the geometric potential, the actual build rate experienced downhole will vary due to several factors:
- Hole Over-gauge: If the hole size is larger than the bit size (washed out), the effective stabilizer contact point shifts, reducing the build rate.
- Formation Hardness: Softer formations may allow the bit to erode the wellbore wall laterally, affecting the turn.
- Stabilizer Wear: An under-gauge top stabilizer acts like a longer "L" value or reduced bend, decreasing the build rate.
- WOB (Weight on Bit): Higher WOB can flex the motor assembly, potentially increasing the build rate in certain setups.
Why is Build Rate Important?
In directional drilling, maintaining the correct Dogleg Severity (DLS) is crucial. If the build rate is too low, the wellbore may miss the target zone. If the build rate is too high (excessive dogleg), it can create a "tortuous" wellbore, leading to problems running casing, stuck pipe, or key-seating later in the drilling program. Using this calculator helps DDs select the correct motor bend setting before running in hole (RIH).
function calculateBuildRate() {
// Get inputs
var bendInput = document.getElementById('bendAngle');
var lengthInput = document.getElementById('motorLength');
var slideInput = document.getElementById('slideLength');
var bend = parseFloat(bendInput.value);
var length = parseFloat(lengthInput.value);
var slide = parseFloat(slideInput.value);
// Validation
if (isNaN(bend) || bend < 0) {
alert("Please enter a valid Bend Setting (Degrees).");
return;
}
if (isNaN(length) || length <= 0) {
alert("Please enter a valid Bit to Stabilizer Length (must be greater than 0).");
return;
}
if (isNaN(slide) || slide 0) {
radius = 5729.58 / buildRate;
}
// Update DOM
document.getElementById('resBuildRate').innerHTML = buildRate.toFixed(2) + "
° / 100ft";
document.getElementById('resTotalChange').innerHTML = totalChange.toFixed(2) + "°";
document.getElementById('resRadius').innerHTML = radius.toFixed(0) + "
ft";
}