Evaluation of the Clinging Constant in Surge- and Swab Pressures

Abstract

The objective of this Master thesis was to evaluate the clinging constant (CL) for Newtonian fluid in a Laminar flow regime in turns of the viscosity, pipe tripping speed and the annular space. The clinging constant is used to describe the apparent contribution of pipe velocity on the pressure drop when considering surge‐ and swab pressures.

The clinging constant is based on the amount of drilling fluid that clings to the pipe wall when tripping, due to the no‐slip  velocity at a drill pipe surface. There are two volume changes in opposite directions that occur when a pipe is tripped in‐ or out of the wellbore: The volume of drilling fluid that sticks to the pipe, and the volume of drilling fluid that goes in the opposite direction to fill up the space after the drillpipe (or that gets displaced when the pipe is tripped in). The clinging constant is derived by using these volume rates.

Since  the  definition  of  the clinging  constant  was  unknown,  it  had  to  be  defined.  Two definitions were made (Chapter 4) and evaluated against each other iin Chapter 6. As a result, three equations of the clinging constant were derived in terms of the three variables.

A Standard Case was defined to evaluate the variables (later redefined into Standard Case 2). The objective was to evaluate the effect that one variable had on CL. The other variables were not supposed to make any impact on the correlation obtained be tween the variable and the clinging effect.

The results showed that all of the variables affected the clinging constant. The annular clearance was the variable that affected CL the most.

The  model  is  based  on  many  assumptions  which  give  uncertainties to  the  equations obtained. The method used to obtain the clinging radiuses (to find the two volume parts) was numerical, which is another source of error. The results were eval uated in Chapter 6 including some further improvements. The conclusion, with the equation s from Chapter 5, is given in Chapter 7.