Concentric Coiled Tubing, Proven Sand Cleanout Technology for Sub-Hydrostatic Wells in Caspian Sea

Abstract

Index of sand production is one of the major issues faced in oil and gas wells on the Caspian region. Although there are multiple technologies to address this issue, the application of these technologies require the well to be cleaned before proceeding with any kind of remedial application. Concentric Coiled Tubing (CCT) sand vacuuming technology has brought a massive advantage for efficiently cleaning the wellbore of sub-hydrostatic wells in Caspian Sea. CCT system is the Coiled tubing string inside of Coiled tubing string which essentially provides a smaller second annular return route for the wellbore solids while simultaneously boosting the return pressure and allowing us to clean the sand where the bottomhole pressure (BHP) is low and not enough to support the circulation of fluids used for the cleanout. Cleanout fluid is pumped through the inner string to power the downhole jet pump comprised in CCT bottomhole assembly (BHA) which creates a drawdown that vacuums the solids and circulates the solids back to surface via the CCT annulus. The solid performance of the CCT system has an established track record worldwide and application of this sand cleanout technology brought a solution for recovering many wells with low BHP and has been successfully implemented since 2013, providing a method for cleaning out tons of accumulated sand particles from challenging wells in Caspian Region. With the complex system being used for cleaning out sand and also surface handling of the solids in the return flow from the wellbore, CCT sand vacuuming technology has proven to be effectively functioning in all cases that it was selected for so far. This Paper reviews the design and mechanism of the CCT sand/well vacuuming system as well as the results of several well intervention cases with its successful execution and lessons learned in Caspian region.