Optimization of Balanced-Plug Cementing

Abstract

Summary Placing properly balanced cement plugs in wells has been a serious problem to the drilling industry for decades. The cement plug is rarely found at the desired depth. Because of the fact that the cement slurry usually is more dense than the well fluid, the cement plugs are found deeper than anticipated, and the quality of the cement plug further down may be doubtful. This often results in setting a new cement plug to proceed with operations such as kickoff in the wellbore, abandonment, or pulling the blowout preventer. In the North Sea area cement plugs fail in more than 25% of the cases. Several techniques have been developed to keep the cement in place, but they are either very time consuming or they have a low degree of success. A tool has been developed that is deployed below the cement plug, preventing the cement slurry from escaping down the well. This tool is very easy to install, does not take extra rig time and covers all sizes of hole diameters, from 152.4 to 584.2 mm (6 to 23 in.), with one tool. Before field application, the system was tested in full scale, where cement plugs were set in casings both with and without the new tool. The result from this testing showed that the new tool had a very high degree of efficiency compared to the reference tests that were performed without the tool. This paper presents the results from the tests and case histories where the tool was used.