Slug Calculations

Introduction

At times, it may be necessary to depress the standing fluid level in the drill pipe or working string with a CBF in the hole. A slug fluid is usually a stock blending fluid like 11.6 lb/gal CaCl₂, 14.2 lb/gal CaBr₂, or 19.2 lb/gal Zn/CaBr₂, depending on the type of fluid being used as the working fluid.

This is a three step process:

1. Find the pressure differential (P_dif) needed to attain the number of feet of dry or empty working string.

EQUATION 19.

2. Knowing the weight of the stock slug fluid, calculate the number of feet required (h_slug) to achieve the desired depression in the fluid level.

EQUATION 20.

3. Convert the feet of slug fluid to volume of slug fluid in barrels (v_slug) using the inside volume of the drill pipe from Table 17, "API Drill Pipe Capacity and Displacement," or Table 19, "API Tubing — Weight, Dimensions, and Capacities."

EQUATION 21.

EXAMPLE N. Balanced Pill in a Known Interval