This consideration is important in highly deviated and horizontal wellbores. The total volume of liquid or shape of the hole have no influence on hydrostatic pressure, but the height of the liquid column (depth) must be measured in the same direction as the force due to gravity, that is, true vertical. The height of the liquid column (depth).The hydrostatic pressure at any point in a wellbore filled with liquid drilling fluid (mud) under static conditions (that is, not circulating and/or not moving the drill string up or down) is a function of only two variables: Mud weight is the key pressure gauge used in drilling since it responds directly to formation pressure. 1 Hydrostatic pressure in liquid columns.Total percentage hydraulic horsepower at the bit Hydraulic horsepower per square inch area of bit Percentage of total horsepower expended at bit Displacement is the volume between the outside diameter and inside diameter of a drillpipe or collar.Ĭapacity volume the volume contained inside a drill pipe or collar Hole volume the volume of the open or cased holeĪnnular volume the volume of the annulus, the area between the outside of the drillpipe or collar and the open or cased holeĭisplacement volume the volume displaced by the steel volume of drillpipe or collar.
Table 1 Definitions of terms and abbreviations used in this chapter Definitions of the mathematical variables and abbreviations used in this chapter are given in Table 1. The results from these calculations increase knowledge of well behavior and facilitate communication with drilling personnel. A few simple mathematical formulas are used to make key calculations during the drilling of a well.
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