This paper presents a historical view and present status of retractable bit design and drilling results. Despite the significant improvements in cone-sealed bearing rock bits, the special features of retractable bits provides a wider range of field applications. Scientific drilling, both continental and offshore and stratigraphic offshore boreholes, is an area for profitable application of retractable bits with a downhole motor. Another promising application is drilling and simultaneous casing where some prototypes have been successfully tested. Other applications such as horizontal and geothermal drilling look promising for future developments.

One of the widely used systems for offshore oil production in water depths up to 500–2500 meters is a steel catenary riser (SCR). Requirements for long-term corrosion resistance of SCR are very stringent, that obliges to manufacture it from expensive steels. Still, the increased water depth leads to increased riser tension, grown pressure, aggravated buckling and oscillation problems. Among alternative materials to manufacture catenary risers, i.e., steel, titanium and aluminum alloys, the aluminum is the best from the “Strength/Weight/Cost” aspects with its high corrosion strength. Design of an aluminum catenary production riser (ACPR) was developed in Russia; and comprehensive tests were performed on mechanical characteristics and corrosion resistance properties of ACPR tubes and their connections. Two possible connections of riser sections were considered, i.e., welded and threaded. Strength analysis of threaded connection was performed by FEM. Mechanical testing included: testing of small samples of pipe material and welded connection cut out of riser section, testing of full-scale specimens of connection prototypes, and measurement of residual stresses. Structural and corrosion tests of samples consist of investigation of standard metallographic characteristics of pipe material and welded connection, and assessment of effects of different types of corrosion in seawater and oil fluid. The results of performed work have led to the conclusion that welded connection is most prospective for ACPR manufacturing. At the same time, the testing revealed certain improvements need to be done in the course of further work on this project.

Aluminum alloys continue to be among the promising materials for manufacture of drill pipes and risers for deepwater and ultra-deepwater environment. Steel tool-joints attached to aluminum alloy pipes increase the number of make-ups and break-outs. Currently, aluminum drill pipes (ADP) are assembled by “cold” or “hot” methods. By the first method, the pin and box are screwed on the pipe with a “sufficiently” high specified make-up torque. By the second method, the pin and box of the tool joint are heated and screwed on the ends of the pipe without effort. After cooling, the shrinkage of the tool joint units creates a reliable permanent threaded “pipe – tool joint” connection. The first method is easier than the second one; however the comparative strength of these ADP connections has not been enough clear. The paper presents the results of comparative strength analysis of both types of connection after assembly at applying tensile load and alternating bending load. The theoretical aspect of the study includes a detailed FEA of “hot” and “cold” assembly connections at applying tensile load and alternating bending load with SCF evaluation. The experimental data are presented as the results of tensile testing of small-scale specimens, removed from different aluminum pipe sections that were heated during “hot” assembly. Finally, full-scale specimens of both types of connections were tested for tensile capacity and fatigue. The comparative strength of both types of connections is concluded.

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Aluminum alloys are among the most promising materials for manufacture of drill pipes for deepwater and ultra-deepwater drilling in corrosive environment. Aluminum drill pipes are made with steel tool-joints to increase the number of connection makings-and-breakings. One of the major concerns of aluminum drill pipe operation in deepwater complex profile wells is the fatigue of their connection. This paper presents the results of study of fatigue properties of aluminum alloy 1953T1 Light Alloy Drill Pipes of Improved Dependability (LAIDP) 147×13 mm that are most extensively used in Russia. During assembly, the pin and box of steel tool-joint are heated and screwed on the tubular ends. After cooling, this assembly provides a reliable permanent connection. The study includes experimental determination of the S-N curve of small-scale specimens of aluminum tubular, FEA of the connection with the SCF determined and fatigue testing of the full-scale LAIDP connection. FEA is based on 3D model. The material properties of tubular are modeled as elastic-plastic. The distribution of hot-assembly stresses is considered in detail. Alternating bending load is applied by several semi-cycles. The results of analysis of Stress Concentration Factor (SCF) at various axial loads, bending moment ranges, friction factors of contact surfaces and interference of connection are given. Full-scale fatigue testing of connection specimen is carried out to verify the results of analysis.