Compressibility Factor On Displacement Oil Base Mud [PDF]

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Compressibility factor on Displacement Oil Base Mud

Yaps this problem will commonly occurs when you handle cement job with Oil Base Mud (OBM) as displacement for it. Due to nominal casing capacity vs actual casing capacity, to prevent miscalculation for displacement for it before cement job execute, we can calculate it and discuss to the operators representative on field for determining displacement volume for cementing operation. Fluids compressibility can be estimated using formula from Petroleum Engineer equations and Rules of Thumbs to determine the changes in volume that occurs with pressure changes. As shown below

Where: : Changes in mud volume resulting from increased pressure, bbl : Changes in pressure applied to fluid, Psi V

: Volume of mud in zero psig, bbl : Fraction percent of water, dimensionless : Fraction percent of synthetic fluid, dimensionless : Fraction percent of solid, dimensionless

In application, fluid compressibility is generally only significant when oil base mud (OBM) used. Therefore, in following example, a typical OBM used. = 1150 Psi V

= 1500 bbl = 37% or 0.37 = 53% or 0.53

= 10% or 0.10

Therefore

Result in mud volume changes when 1150 psi applied to 1500 bbl is 6.39 bbl. With shoe track volume 8 – 12 bbl, displacement would be stopped before plugs landing on collar, if fluids compressibility calculation is not consider before cementing operation execute. Note: To determine the ΔP that would apply to entire fluid column, estimate the hydrostatic pressure at true vertical depth (TVD) and divide by 2. This midpoint will apply to the entire volume (assuming a near vertical well), for extended reach horizontal well, a depth closer to TVD should be considered. Remember, especially when using OBM, accurate displacement volume can be determined when fluids compressibility has been consider before cementing operation.

Thanks to: Hank Rogers, The Cementer.