Enter the static mud weight (MW), the circulating effect expressed as an equivalent mud-weight increase (ΔECD = ECD − MW), and any other pressure effects expressed as an equivalent mud-weight increase (ΔAOPE) into the calculator to determine the EMW. If you have a pressure at a given depth and want the EMW directly, use the “Pressure/Depth/EMW” tab.

EMW (Equivalent Mud Weight) Calculator

Enter any 3 values to calculate the missing variable. Note: ΔECD and ΔAOPE must be entered as mud-weight-equivalent increases (not pressures).

EMW Formula

The following component form can be used when each effect is expressed as an equivalent mud-weight contribution (at the same depth). 

EMW = MW + ΔECD + ΔAOPE
  • Where EMW is the equivalent mud weight (the mud weight that would create the same pressure at a given true vertical depth)
  • MW is the static mud weight
  • ΔECD is the increase due to circulating pressure losses expressed as an equivalent mud-weight increase (ΔECD = ECD − MW)
  • ΔAOPE is the sum of any other pressure effects expressed as an equivalent mud-weight increase (for example surge/swab or applied backpressure)

To calculate EMW from components, add the static mud weight (MW) plus the circulating contribution (ΔECD) plus any other contributions (ΔAOPE), with all terms expressed in the same mud-weight units (ppg, kg/m³, or g/cm³). If you instead know a pressure P at depth TVD, a common field-unit relationship is: EMW (ppg) = P (psi) / (0.052 × TVD (ft)).

What is EMW?

Definition:

EMW, short for equivalent mud weight, is the equivalent fluid density (mud weight) that would produce a specified pressure at a specified true vertical depth. It is commonly used to express bottomhole pressure effects (such as circulating friction losses, surge/swab, or applied surface backpressure) in mud-weight units.

How to calculate EMW?

Example Problem:

The following example outlines how to calculate EMW using the component form above.

First, determine the static mud weight. For this example, the static mud weight is 9.2 ppg.

Next, determine the circulating contribution expressed as an equivalent mud-weight increase (ΔECD = ECD − MW). In this case, ΔECD is 0.8 ppg.

Next, determine any other pressure effects expressed as an equivalent mud-weight increase (ΔAOPE). For this example, ΔAOPE is 0.3 ppg.

Finally, calculate the EMW using the formula above:

EMW = MW + ΔECD + ΔAOPE

EMW = 9.2 + 0.8 + 0.3

EMW = 10.3 ppg