Concentric Coiled Tubing Vacuum Technology (CCTVT) was developed in the mid 1990s in Canada, and since then has spread worldwide. The technology was initially focused on sand cleanouts in heavy-oil, low-pressure, deviated wells, where other cleanout methods, including conventional CT interventions, were inefficient. Under such conditions, CCTVT provided a simple but very effective solution.
In general terms, the technology comprises a downhole jet pump run on a concentric coiled tubing (CCT), which is a coiled tubing string inside another coiled tubing string. A single-phase fluid is pumped through the inner string to power the downhole jet pump, creating a localized drawdown that vacuums well fill (fluids and/or solids), increases the return pressure, and circulates fluids and solids back to surface via the CCT annulus.
Since the introduction of this technology, it has gone through several updates in order to face new challenges. The latest BHA versions include multiple operational modes to improve cleanout efficiency, minimize runs, function with supplementary tools and most recently, to accommodate a specialized electric conductor to run a real-time logging tool in conjunction with the jet pump.
Currently, the application of the system has extended beyond solids removal on heavy oil, onshore wells. The current work scope ranges from very simple operations such as drilling fluid and filter cake removal, liquid unloading, inflow profiling, evaluating completion integrity, matrix stimulation, pressure and temperature logging, etc.; to more complex and challenging operations such as memory production logging, H2S inhibition, multilateral wells, chemical sand consolidation, hydrate removal and realtime production logging. These operations are occurring in the full range of oilfield locations: onshore and offshore wells, from fixed installations to mobile rigs, in jungle to arctic conditions.
This paper will summarize the new techniques that are being applied in many global locations with CCTVT. Each technique will be illustrated with case histories detailing time and cost savings and, where relevant, production improvements.