In arctic areas such as north ALASKA in the U.S., the subsidence of surface ground occurs due to the melting of the ground. This causes tension or compression displacement and strain on the casing in the well. In order to estimate a displacement and a strain loading limit for 13 3/8", 68 LBS/FT L-80 HF-ERW buttress casing, a series of full scale compression and tension tests were carried out. The compression test results show that this casing can be strained to a 1.5 percent strain without bulging or leakage of internal pressure and this casing can be deformed to about a 10 percent large-scale deformation without failure. These two test specimens experienced two shell buckled area near the buttress collar and they were not related to the weld seam. The tension test results show that the tensile strain limit is about a 4.6 percent axial large-scale deformation. The thread jump out occurred during loading to a 5.0 percent strain. All measured strengths were much higher than the API requirement.
The surface of the earth in extremely cold region, such as the north ALASKA of the U.S. is covered with a perennially frozen soil called permafrost. Casing used in oil well drilled in these areas are subjected to complex strain induced by the melting and sinking of the permafrost. For example, it is understood that tensile stress acts on casing in a detrital-granular soil and compressive in a clay soil. The base metal and joints of casings used under such conditions are required to have adequate strength to withstand such tensile and compressive stresses. This paper discussed the deformation and fracturing behavior of casing revealed by the compressive strains assumed to results from the melting and sinking of the permafrost layer.
