| Popis: |
Abstract Development of oil and gas fields with high H2S and CO2 content in formation fluids is one of the challenges for modern technology. Conventional steel casing and tubing strings cannot be used in such environments as they are much prone to corrosion, while the use of specialized corrosion-resistant tubulars with high content of chrome makes well construction and operation times more expensive. Such extreme operating conditions prevail in the fields located in the North of Komi Republic, where H2S content is above 15%. In addition to the corrosive environment of the wells, the drilling rigs, which operate in the area have limited load capacity and therefore face difficulties in running a single-section casing strings to depths over 4000 meters. A very promising approach to elimination of these problems may be the application of aluminium alloy casing pipes developed by Aquatic Company. It is known that aluminium alloy pipes remain inert to corrosion even if the formation environment is fully saturated with H2S and/or CO2. They are also light-weight, have high strength-to-weight ratio, and thus decrease the existing tensions in the string and reduce well construction costs. Description of the oilfield for application test Bayandyskoye oilfield, belonging to "LUKOIL-Komi" LLC, where aluminium casing and tubing were planned for trial application, had the major problem of hydrogen sulfide presence in formation fluids: up 18.5% vol. in the Zadonsky horizon of Upper Devon and carbon dioxide up to 1.1% vol. Besides, well conditions were characterized with high formation pressures up to 27 MPa and temperatures up to 90°C. Prevalence of such aggressive conditions set special requirements for well construction, casing, completion type, wellhead, BOP and drilling equipment, as well as for locations of drilling equipment. Because of these reasons, the first two exploratory wells on the Bayandyskoye oilfield were drilled from rigs equipped with a power top drive, with corrosion-resistant BOP with blind rams, pipe rams and shear rams, and with an annular preventer. Initially aluminium tubulars were not considered for the design of the well. The well construction of first two exploratory wells was rather metal-intensive and costly. It included two intermediate strings (D=323.9 mm, L=2460 m and D=244.5 mm, L=3483 m) and a production string D=168.3 mm to target depth of 4588 m. Great care was exercised when selecting the material for casing and their leak-proofness. The upper section of the second intermediate string (D=244.5 mm) utilized 90SS pipes of strength group, and the lower section was made of Sanicro 29 (110) stainless steel pipes. All casing pipes came with highly sealed Tenaris Blue threaded connections. Casing equipment (stage cementing collars, packers, valves) was also made with similar high-strength corrosion-resistant steel grades. The intermediate strings were run in hole by sections with the use of docking tools, which increased the time of construction, risk of faults and emergencies in the process of running in hole and casing of wells. |
