## Stinger or Tailpipe Placement of Cement Plugs

The most common method used for the placement of cement plugs is the balanced-plug method using drillpipe, tubing, or a combination of both. A stinger with a smaller diameter than the drillpipe is commonly run on the bottom of the drillpipe for setting a balanced plug. However, a mathematical analysis of what occurs once dynamic conditions are initiated by pulling out of hole (POOH) with a small-diameter stinger shows that the initially balanced system quickly becomes unbalanced.

## Introduction

The balanced-plug method of calculating plug-placement volumes has long been a standard industry practice for setting plugs in the wellbore. Volumes are calculated in such a way that all fluids both inside and outside of the pipe are at the same height, thus resulting in a hydrostatically balanced system.

The basic assumption behind the balanced-plug calculation method is that the fluid is going to remain in place while the drillpipe is simply pulled through the fluids with minimal falling of the fluid level to fill the void left behind by the metal displacement of the drillpipe. This assumption is correct, neglecting the frictional drag forces on the fluid, when the drillpipe outer diameter (OD) and inner diameter (ID) are the same from top to bottom. However, when the drillpipe includes a stinger at the bottom, there is a disruption in the hydrostatic equilibrium between the column of fluid inside and outside the drillpipe, resulting in flow at the bottom of the stinger between the two regions.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 168005, “Don’t Get Stung Setting Balanced Cement Plugs: A Look at Current Industry Practices for Placing Cement Plugs in a Wellbore Using a Stinger or Tailpipe,” by Justin Roye, Schlumberger, and Sam Pickett, Chesapeake, prepared for the 2014 IADC/SPE Drilling Conference and Exhibition, Fort Worth, Texas, USA, 4–6 March. The paper has not been peer reviewed.
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Stinger or Tailpipe Placement of Cement Plugs

01 May 2014

Volume: 66 | Issue: 5

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