Successful Placement of Cement Plugs in HP/HT Wells Using an Innovative Computer-Aided Simulator

Abstract

Placing cement plugs in high-pressure/high-temperature (HP/HT) wells represents a big challenge, from the standpoint of both the chemistry and the placement techniques. Any failure to properly place a cement plug will lead to costly nonproductive time and will require repeating the job, which represents even more technical and operational challenges because of the downhole uncertainties. West China's Tarim basin experienced these challenges for HP/HT sidetrack, plugback, loss circulation, and abandonment cement plugs, with wellbore depth over 6500 m and bottomhole temperature over 160 °C. To improve the success rate of placing cement plugs, thorough analysis of well information was done, and novel placement software was implemented to help ensure a successful placement. The new computer-aided model is a risk-based model that takes into account the downhole well conditions to analyze and display the fluid interfaces of mixing, both while traveling inside the pipe and in the annulus. The result is the assessment of the possible contamination of the cement slurry after pulling the pipe out of the hole and a recommendation for the best fit to execute a successful cement plug. The results obtained with the new engineering tool and precise operational field executions allowed the operator to execute more than 80 cement plugs successfully from 2010 to 2013.