U Tubing Related To Primary Cementing

For some time, the Petroleum Industry has recognized that fluids will experience "U-tubing" at some point during the placement in the wellbore. This "vacuum" effect has been especially noticeable during primary cementing operations, and it is largely attributed to the fact that the fluids used in cementing often are more dense than those originally in the wellbore. The phenomenon of the U-tube effect, although recognized, has never been fully understood. To better understand and predict this phenomenon, a mathematical algorithm has been developed to aid in analyzing fluid placement in the wellbore. It is based on a mass balance, an energy balance, a modified Bernoulli equation, and a full tracking routine to analyze fluid placement. Discussions encompassed in this paper will be to define the U-tube phenomenon, to evaluate its effects relating to cementing techniques, and to present an actual liner job in comparison to predictions made by this algorithm.