Application of fuzzy logic for risk assessment of investment projects

Abstract

Comparison of the stress-strain state of a drill-string section for two cases of its position in the well interval with a cavern is aim of the article. The drill pipe body is placed in the middle of a cavern in a first case and the drill pipe tool joint is placed in the middle of a cavern in a second case. The method of finite elements that is realized in the engineering simulation software is used for research. The precise geometrical parameters of the drill pipes including a upset part and a screw joint; the character of the contact between a drill string and a well side; the physical and mechanical parameters of the rock; acting of the weight, the axial force, the bending moment and the torque are considered in to account during the calculation. The results of the calculation show that difference between the magnitudes of the normal stress on the drill pipe surface for mentioned above two cases is 45%; the difference between maximal bending is 65%. Totally, our research shows that position of the drill string relatively to a well side with a cavern acts on its stress-strain state with another changeless conditions. It means that proposed in this article calculations are recommended for the dangerous well intervals. Keywords: drill string; stress; strain; cavern.