The drilling of shallow horizontal wells in unconsolidated sand formations faces the particular challenge of achieving proper well trajectory, needed that minimizes dog leg severity and if not accomplished can increase well intervention frequency. These well complexity challenges may result in improper wellbore sand clean outs that can promote early failure of the artificial lift equipment and increase the frequency of interventions that cause production deferment. Wellbore clean out operations are risky because of potential fluid losses and low reservoir fracture pressures, which limit downhole clean-out circulating pressures.
Concentric Coiled Tubing (CCT) technology has been used to clean out horizontal slotted liner sections with suspected sand fill. This sand fill reduces well productivity due to sand bridging within the slotted liner. The application of CCT technology reduces the risk of lost or limited fluid returns and provides an effective clean out method. In addition, it can also provide drawdown at the CCT power head, resulting in lost workover fluids from the wellbore effectively removed by using the system under vacuum-mode. The multiple operating system modes provide the benefit of cleaning and treating the wellbore in the same run.
Workover interventions using conventional CT have been used in the past with limited success. Moreover, in some cases, these wells have showed sharp production declines after post CT clean-out operations. It was suspected that in addition to sand fill issues, formation damage has occurred in these wells due to the fluids used during those interventions. The application of CCT has resulted in the removal of sand and lost clean-out fluids previously used.
This paper reviews the wells, which have had conventional cleanout methods done that were unsuccessful and provides the results of using CCT technology to restore well production thus reducing well interventions by 50% and OPEX savings up to 15%.