A checking method for test string with expansion joints in ultra-deep wells
As the key target on ultra-deep gas reservoirs deployed by Sinopec in northeastern Sichuan Basin,the Middle Permian Ma-okou Formation is characterized by deep burial depth,high temperature,ultra-high pressure,and rich hydrogen sulfide.The previous test string was not good enough for Maokou reservoirs in terms of performance and structure due to poor properties and low safety factor.And the string is hard to design and risky in such reservoirs.Thus,considered the needs of exploration and evaluation on the Maokou Formation in this area,a checking method suitable for the test string in ultra-deep and ultra-high pressure wells was estab-lished to optimize both quantity and position of expansion joints by analyzing joint's force and string's mechanical behaviors,and checking string's intensity.Its application indicates that(i)a mechanical model is constructed for the string with joints in ultra-deep wells with high temperature and pressure by considering the controls of piston,buckling,and swelling and temperature effects together with expansion joints on the force and deformation of downhole string;and(ii)the optimized string makes acid fracturing and data ac-quisition in such wells a success,proving the reliability of this method.All research results not only offer strong support for ensuring this formation in the safe and efficient exploration and development,but are of great significance for advancing the exploration and development of deep-seated oil and gas resources.
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