The Research Of Environment And Safety Risk Assessment System For Exploitation Of Gas Field With High Content Of Hydrogen Sulfide

The gas fields with high content of hydrogen sulfide in China mostly located in Sichuan basin. The two-part gas fields in Sichuan basin contain hydrogen sulfide. In period of the“Tenth Five-year Plan”, 99 billion m3 gas fields with high content of hydrogen sulfide have been discovered in the Sichuan province. On account of causticity and toxicity of H2S, the safety of exploitation of gas field with high content of hydrogen sulfide should be essentially regarded. Owing to the complexity of gas field with high content of hydrogen sulfide and uncontrolled factors such as environment and climate, it is essentially needed to carry out research of environment and safety risk assessment of gas field with high content of hydrogen sulfide.The northeast of Sichuan province has been the main target from which PetroChina will expedite the development of natural gas industry and Sichuan gas field will increase production and reserves of natural gas. The gas field in Sichuan basin is characterized by carbonate rock cranny and secondary generation gas field. Owing to high content of hydrogen sulfide in the gas field, Sichuan basin, the risk of exploitation is very high. The essential problems in exploitation of gas field with high content of hydrogen sulfide are to carry on research of corrosion mechanism of material affected by H2S and to formulate the corresponding safety measures according to the drilling well site condition. Thereby, it’s very significant to carry on the research of risk assessment for exploitation of gas field with high content of hydrogen sulfide.Research has summarized the actuality of research in risk assessment and HSE management system applied in the petroleum industry at home and abroad. Risk of exploitation of gas field with high content of hydrogen sulfide has been identified and the main risk factors have been ascertained with application of Fault Tree Analysis.Research has carried out corrosion experiments of material according to the simulated exploitation condition. Corrosion experiments of material include: (1) corrosion performance of well tubing and casing affected by H2S, which comprises capability assessment of stress of crack of well tubing to resist sulfide and electrochemistry corrosion of material affected by H2S, these experiments were carried out at lab and drilling well site respectively; (2) electrochemistry corrosion performance of ground steel pipe affected by H2S; (3) steel well tubing and casing affected by high speed current, which comprises calculation of dimension of well tubing and sleeve which are limited by corrosion problem, and experiment of well tubing affected by current in exploiting gas field. Research has summarized the corrosion performance of several materials tested in experiments and corrosion mechanism of material affected by H2S. Research ascertained the index and risk grade estimation method in risk factors of risk assessment system according to data obtained in experiments.According to the character of risk in exploitation of gas field with high content of hydrogen sulfide, analytic hierarchy process has been applied to establish the hierarchy model of environment and safety risk assessment for exploitation of gas field with high content of hydrogen sulfide and establish the risk assessment system. Research completed the classification of overall risk grade in risk assessment system and developed computer software for the established risk assessment system. The risk assessment system has been applied to assess the risk grade of Well 11 site in Luojiazhai gas field located in northeast of Sichuan province and got a consistent result. The result proves that established risk assessment model system is authentic. Measures have been put forward to decrease the risk of well site.