The effect of pre-stretching and under-aging treatment on microstructure and fatigue crack resistance of Al-4.1Cu-1.27Mg-0.47Mn-0.02Ti alloy has been investigated in present work. The results showed that the fatigue strength corresponding to 107 stress cycle numbers of the sample pre-stretched 4% and under-aged at for 2 hours reached up to 280MPa, 80MPa higher than that pre-stretched 0% and peak-aged at for 8 hours. Microstructural observations showed that fine and uniformly dispersed S’ plates were present in the sample treated by pre-stretching and under-aging, whereas, a coarse S’ plate was formed in the sample when treated by 0% pre-stretching and peak-aging. It is indicated that the pre-stretching and under-aging treatment promotes the dispersoid formation of strengthening particles, enhancing the fatigue crack resistance and resultant fatigue strength. Keywords: Al-Cu-Mg alloy, fatigue, pre-stretching, aluminum alloy casing pipe

In TK oilfield, there is a large content of carbonatite in cambrian-ordovician, with great depth 4500m-6300m, high temperature 120oC -140oC, anisotropy, developed fracture system and complexity in geological structure. This paper is concerned about wellbore collapse in open hole completion of well R1 and other wells in the collepse well area, and trying to solve this problem through statistics of collapsed wells, and calculate with the mechanics model coupled with temperature field, fluid flow field and rock-mud physicochemical reactions. The result show that the development of hydration stress in planes of weakness, occurrence of nature fractures and technic stress are the most influential factors on wellbore stability. A wellbore in a formation with nature fractures around the wellbore has a testing pressure difference window of 21-28MPa.