Improvements in Production Liner Cementing for Coiled Tubing Drilling

Abstract

Since 1994 Coiled Tubing Drilling (CTD) has completed over 650 sidetracks on the North Slope of Alaska. In many aspects the window milling and drilling phase can be considered a mature technology. However, recent developments in the completion phase namely with the generation II side exhaust liner running tool (Gen II SELRT) have further increased job reliability, safety, and efficiency for the liner cementing completion phase. This paper will begin with a brief update on the status of CTD on the North Slope (3 rigs drilling on a daily basis) and discuss how many of the challenges with drilling through/below the production tubing have been dealt with. The cost for a CTD sidetrack with an equivalent amount of reservoir exposure and zonal isolation is about one half that of a rotary sidetrack on the North Slope. This is due to efficiencies in leaving the production tubing in place (dominant savings) and less consumables. In addition, CTD’s enhanced capability for underbalanced drilling (UBD) and managed pressure drilling (MPD) make it attractive for some North Slope fields. While the electronically controlled drilling bottomhole assembly (BHA) has improved drilling performance, the electric line (EL) inside the CT has challenged the completion phase. CT wiper darts for separating cement from displacement fluid can no longer be used. The CT wiper dart would be damaged by the EL and visa versa. Instead, the new liner running tool discussed in this paper exhausts the contaminated cement/mud interface to the annulus at top of liner before launching the liner wiper plug (LWP). Over 76 liners have been cemented with the side exhaust technique. The last 34 jobs have been done with the Gen II SELRT that uses mechanical dogs to close the path through the LWP, side exhaust, and launch the LWP when desired. This new tool increases job efficiency over the first generation tool and continues to provide reliable liner cementing with EL in the coil.