Cementing Through Capillary Tubing to Meet Regulatory Requirements: A Novel Approach for Plug and Abandonment

Capillary tubing has traditionally been used for various downhole chemical treatments applied to enhancing fluid loading, treating corrosion and scale buildup, and preventing paraffin and emulsion formation. Capillary tubing provides an advantage over coiled tubing due to its lighter weight, smaller footprint, mobile structure, faster running speeds, and more economical costs. One drawback however, is the increased friction pressures when pumping abrasive fluids. Typical capillary tubing is sized from ¼ to ¾ in. OD versus the more common coiled tubing, which ranges from 1 to 3 ½ in. OD. Therefore, the use of capillary tubing for cementing operations has not been considered until recently. This paper will feature a project in Australia where a capillary unit was employed to abandon a well with cement, while concurrently installing downhole pressure gauges to comply with local regulations. The cement design criteria along with two case histories will be described, and lessons learned will be evaluated. Data that has been collected through the various jobs will demonstrate that current simulation software will need to be modified to match pressure outputs witnessed in the field. A comparison of simulated versus actual job pressure data has shown as much as a 70% friction reduction in actual pressure readings. The witnessed pressure values are shown to be consistent over several operations; therefore a theoretical correlation can be drawn so more realistic values can be simulated in the future. Additionally, slurry designs which were proven successful and operational considerations for improved job quality will be discussed. This paper will discuss two case histories in which capillary tubing was used for the first time in Australia. Methodology, limitations, and future improvement possibilities will be discussed in detail throughout this paper.