Reliability And Safety Assessment Of Well Structure In The High-Sulphur Gas Field

Well structure is the important aspect to well drilling and well completion of Oil and Gas Well Engineering, the rationality and security of well structure design is key factor to the success of drilling and completion, especially for the three-high gas field(high-pressure, high-production, high-sulphur), where continental sedimentation and marine deposit interaction,pressure prediction difficult, and exist many sets of pressure system in whole well, the rational well structure design is particularly important to the drilling and completion.This paper has studied the safety evaluation techniques of well structure based on the indefinite formation pressure in high-sulphur gas field, has established a evaluation system of well structure, including two parts. Firstly, risk probability method, has analysed the potential risks of well structure, utilized the triangular distribution of subjective probability and objective probability distribution to evallute formation pressure. With the structural reliability theory, constructed the risk probability models of well structure, including well lost probability model, well kick probability model, well collapse probability model and well stick probability model, and through used mathematical theories and methods of reliability to solve risk models, obtained the total failure probability of well structure. Formed the risk probability method based on Probability calculation. Secondly, Experts' evaluation, based on the uncertainty of statistical data source itself, make full use of engineering and technical personnel at the scene or the experience of the experts to predict the potential risks probability of well structure design, used AHP (The Analytic Hierarchy Process) method to calculate the weight values of experts, obtained the overall evaluation through experts' weight values. Formed the Expert evaluation method based on the experts' experience.Finally, integrated the two methods, compiled risk analysis and safety assessment software of well structure with Visual Basic language, by simulating qingxi 1~# well and puguang 5~# well from Northeast Sichuan, the simulation results are in good agreement with the actual situation, which show that the method can be applied to the safety pre-evaluation of well structure, and can provide a scientific basis for decision making to well structure design at a certain extent.