Mini MCR Calculator Guide

The Mini MCR (Mud to Cuttings Ratio) Kit is a simplified field kit designed to quickly estimate the oil/water retention and mud-on-cuttings ratio without running a full 45-minute retort test. It uses a small, precise gravimetric cell of known volume to determine sample densities and volumetric ratios based on base fluid properties.

This calculator helps engineers make fast, directional adjustments to solids control equipment (like centrifuges and dryers) directly at the rig site.

Input Parameters

To perform a Mini MCR analysis, you will need the following measurements:

1. Gravimetric Weights (grams)

• W1 (Empty Cell): Weight of the clean, empty gravimetric cell assembly.
• W2 (Cell + Mud): Weight of the cell filled with the wet cuttings/mud sample.
• W3 (Topped Up Cell): Weight of the cell after base fluid is added to fill the remaining volume.
  • For OBM: Top up with base oil / diesel (specific gravity ≈ 0.84).
  • For WBM: Top up with water (specific gravity ≈ 1.00).

2. Mud & Equipment Constants

• Mud Weight (MW): The density of the active drilling fluid in the system.
  • Units: ppg or kg/m³ (automatically converted inside the app).
• Cell Volume (V_cell): The volume of the gravimetric cell in milliliters (ml). This is a calibrated constant (configurable in the App Settings, default is usually around 10–25 ml).
• sgForm (Formation Specific Gravity): Specific gravity of the formation rock (typically 2.60).

Step-by-Step Procedure

1. Weigh Empty Cell (W₁): Ensure the cell is clean and dry. Weigh it on a digital pocket scale.
2. Add Sample and Weigh (W₂): Add a scoop of wet cuttings from the discharge stream into the cell. Tap it gently to remove large air gaps, then weigh the cell.
3. Top Up and Weigh (W₃): Fill the remaining volume of the cell to the top with base oil (for OBM) or water (for WBM) until flush with the rim. Clean off any overflow, then record the weight.
4. Compute: Input the weights, active mud weight, and cell volume into the Cutpoint app.

Calculations & Formulas

The app uses the top-up mass differential to calculate true sample volume, density, and volumetric retention:

1. Sample Density (MW_sam)

The volume of the top-up fluid is subtracted from the calibrated cell volume to determine the true cuttings sample volume. The sample weight divided by this volume gives the sample density:

(If metric is selected, the result is converted to kg/L or kg/m³).

2. Mud to Cuttings Ratio (MCR)

Using the calculated sample density (MW_sam) and active mud weight (MW_active), the MCR is determined as:

The final MCR is expressed as a ratio of MCR : 1.

3. Mud on Cuttings Volume Percent (MOC)

The volume percentage of mud on the cuttings sample is calculated as:

4. Mathematical Variance

The app calculates a statistical variance percent (Var) to estimate the deviation of the calculated sample mud density from theoretical expectations based on formation specific gravity (sgForm):

A high variance value may suggest an error in the measurements, base oil specific gravity, or significant air entrapment in the cell sample.