Study On The Performance Of The Oil Casing With Large Expansion Rate

Expandable tube which offers the advantages of high stress and low costs ha s been widely used in oil industrial field. With the expandable tubular technology developing, single borehole diameter drilling and well completion can be achieved. However, many research results revealed that the characteristics of raw material have been the main restricting of the application and development of the technology.Currently, most expandable tube is still made of API casing, of which the expansion rate is less than 25% and the yield ratio is about 0.75. Many researchers devoted themselves to invent a new expandable tubular with high performance, low cost and high expansion rate. However, seldom research focused on the modification of raw materials.In this paper, low carbon alloy steel undergoes heat treatment with different parameters. Attention was paid to the microstructure, mechanical and expansion properties of the treated steel. The influence of parameters, such as cooling rate, quenching temperature, tempering temperature and time on the properties of materials were systematically investigated. The microstructures of the treated steel were analyzed by microscope, scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results show that the dual-phase structure is obtained by the critical quenching process, and the toughness and expansion properties of the steel are improved, compared with that by traditional quenching process. Harden ability of the dual-phase steel is enhanced by adding Cr and Mo elements. The ductility of the dual-phase steel obtained by critical quenching process is significantly improved by tempering. After tempering at 770 oC, Elongation, reduction of area and ultimate expansion capacity of the steel increase to 14.9%, 48.96% and 40%, respectively. Yield strength ratio of the dual-phase steel, which is about 0.65, is less than that of API casing, which is 0.75. It can be concluded that the dualphase expandable tube with high performance, low cost and high expansion rate is obtained by the critical quenching and tempering process.