Eiji Tsuru

An experimental study of casing performance under thermal cycling conditions

The authors have investigated the behavior of casing pipe body and connections under simulated thermal recovery conditions. The study, performed in a new computer-controlled thermal-well simulator, examined the thermal stress behavior and leak resistance of pipe and connections at temperatures up to 354{degrees}C (670{degrees}F) under severe loading conditions similar to those encountered in thermal wells. We also studied the biaxial collapse resistance of the casing under the large axial tension that would exist after the cooling period in a steam-stimulation process. Results indicate that in a steam-injection process in which the casing is maintained at its maximum temperature for a period of time, stress relaxation can occur in a constrained production casing, resulting in the development of excessive tensile stress during the cooling period. Premium connections with metal-to-metal seals maintained gas leak resistance at temperatures up to 354{degrees}C (670{degrees}F), whereas the connections without metal seals did not. The biaxial collapse resistance of casing under large axial tension depended on the stress/strain characteristics of the material.

INNOVATIVE TECHNOLOGY FOR TUBULAR CONNECTION TO ELIMINATE THREAD-COMPOUND GREASE

Doping of thread compound grease may induce some troubles, for example, an environmental pollution, though it must be useful to the performance of tubular connections. This paper deals with an innovate tubular connection made-up without compound grease, and describes the galling resistance and connection performance under field conditions. To develop the new coating technique instead of compound grease, the tribological tests of pin-on-disk type were carried out. For the connections with the new coating, the performance was evaluated by power tongs and full sized testers. As a result, the make-and-break of the connection without any liquid lubricant was realized using the new coating. The connection can maintain the same performance as the conventional connection with compound grease. In conclusion, the quite new premium connection can solve the problems induced by compound grease, and simplify the running works of casing and tubing pipes.

Allowable Torque of Tubular Connection Under Simulated Running and Working Conditions

In field operations, the make-up torque of tubular connections depends on compensated axial weight and environmental temperature. Also, in running operations, torsion can be applied to casings with connections under loading. This paper deals with the torque resistance of tubular connections, with regard to field operating conditions. The results indicate that the make-up torque increases when the grease quantity is small and the temperature is low, and the torque resistance improves under loading. Using the predicted torque resistance, the true safety of the connections can be evaluated for their torsional strength.

Performance of tubular connections under the loading conditions of horizontal wells

This study deals with the negative effects of bending stress and casing wear on tubular connections. The joint strength of three connection types, API long round thread (LTC), API buttress thread (BTC), and typical premium joint (PJ), was measured with a full-size combined loading tester. Measurements were also made for the connections simulating wear induced by drilling operations. The sealing ability of the connections were evaluated under bending and wearing conditions. Numerical simulations were undertaken to investigate the failure mechanism of the connections. The results indicate that LTC joint strength is lowered by bending, though that of BTC and PJ is not degraded. Joint strength is reduced in direct proportion to the wear area ratio of the pipe body. In sealing ability, only the premium connection maintained leak resistance under combined loading with bending. Axial loading is more detrimental to sealing integrity than the bending moment. In conclusion, the connection performance data can be useful in designing safer horizontal well casings.