Steel pipe for embedding-expanding, and method of embedding-expanding oil well steel pipe

A method of embedding oil well steel pipes having smaller diameters one after another comprising:

• selecting a steel pipe to be expanded in a well as part of the embedding method, wherein the selected steel pipe has an eccentric non-uniform wall thickness ratio of 10% or less, and
• embedding a steel pipe in an excavated well,
• further excavating the underground on the front end of the embedded steel pipe to deepen the well,
• inserting a second steel pipe, whose outer diameter is smaller than the inner diameter of the embedded steel pipe, into the embedded steel pipe, and embedding the second steel pipe in the deepened portion of the well,
• expanding the second steel pipe radially by a tool inserted therein to increase the diameter,
• further excavating the underground on the front end of the expanded steel pipe to deepen the well,
• inserting another third steel pipe, whose outer diameter is smaller than the inner diameter of the expanded steel pipe, into the expanded steel pipe, and embedding the third steel pipe in the deepened portion of the well,
• expanding the third steel pipe radially, and repeating said steps;
• wherein the second and third steel pipes are the selected steel pipes and using the selected steel pipes as the second and third steel pipes improves resistance to bending during the expanding steps.