Depending on the application, composite coiled tubing (CCT) may serve as a cost-effective alternative to conventional coiled tubing.1 Gas wells in Alberta, Canada often lose production when hydrates form as a result of temperature drops in gas flow. To reduce gas-flow temperature drop and prevent hydrates from forming, operators commonly use a steel heater string to heat the annular area between the production tubing and casing. Some wells require more heat to reach the critical hydrate temperature depth than others, resulting in higher costs for heating and pumping equipment. To reduce these costs, operators looked for a solution to temperature drop, and found it in CCT. Because of its low thermal conductivity (heat loss), a CCT heater string can reduce the need for upgrading or replacing surface heating and pumping equipment. Introduction In one study, continuous hydrate problems occurred in a newly completed gas well in Alberta when the well was producing at its potential (Fig. 1, Page 4). Operators inserted a 1 ¼-in. outer diameter (OD) steel CT string into the annulus of the well to a depth of 4,593 ft. They then pumped water heated to 167°F down the string to heat the flow of gas above 80°F, the temperature at which hydrates form. The steel CT failed to retain enough heat to prevent hydrate problems. The only way operators could produce the well was to increase the pump rate and reduce gas flow. An alternative to this costly approach would have been to upgrade the heating equipment, but that, too, would have been expensive. A simulation suggested that replacing the steel heater string with a fiberglass or CCT material with low heat loss values (thermal conductivity 1.92 Btu/hour/ft2-in./°F) could be a solution. This method would not require any changes to the surface equipment. Validation To validate the simulation and prove that a heater string with composite properties would be the solution, operators ran a temperature log while the steel tubing string was being used and the well was flowing. When the temperature log was compared with the simulated results [allowing for the thermal conductivity of steel (77.8 BTU/hour/ft2-in./°F)], the results were comparable (Fig. 2, Page 4). Heater-string inlet parameters were as follows:flow rate 16.0 gal/minpressure 600 psitemperature 167°F With this information, well operators investigated the design of a heater string with composite properties. Design Considerations The OD of any heater string would have to fit easily into the area between the 2 7 /8 -in. tubing and 7-in. casing (ID 5.9 in.). This annular space was effectively 1½ in. (Fig. 3, Page 4). The minimum ID of the heater string would have to be 1 in. to maintain the required pump rate of 16 gal/min. Fiberglass jointed tubing was considered for use, but for fiberglass tubing to maintain a 1-in. ID, the OD of the tool joints has to be larger than 1½ in. Fiberglass jointed tubing would not fit into the annular area. Seeking another solution, operators decided to test CCT. CCT Design Because composite coiled tubing can be manufactured to any specification, a final OD of 1.37 in. was chosen, with the ID remaining at 1 in. This OD would allow operators to easily install the string (Table 1, Page 3).