Leakage Control And Emergency Response For Gas Gathering System Of Highly Sour Gas Field

This dissertation is based on the project of"Safe and Effective Exploitation of Highly Sour Gas Field"that is part of the National Key Science and Technology Programs for large oil and gas field exploitation, and the"Development of Emergency Response System for Gas Gathering System of Puguang Sour Gas Filed"and"Safety Control Technology for Gas Gathering Station of Puguang Sour Gas Filed"funded by the"Key Technology Projects for Puguang Gas Field Expolitation"that is part of 2005 "Shi Tiao Long" Science and Technology Programs of China Petrochemical Corporation, in which the leakage control measures and emergency response methods are investigated systemically, and the main research achievements include the analysis of dynamic leakage mechanism of gas gathering equipment, simulation of sour gas dispersion in complex terrain, influence on the hydrogen sulfide poisoning by the rain during sour gas dispersion, the sulfide dioxide hazard and control effectiveness assessment on flaring and venting of sour gas, calculation of emergency planning zone in complex terrain, development of emergency response system for leakage accident of gas gathering system in highly sour gas field, and so on. These works are summarized as follows:1 Analysis of dynamic leakage mechanism for gas gathering equipmentBy analyzing gas processing in the gas gathering system of highly sour gas field, the equipment of the gas gathering system that can result in huge amount of sour gas release and large-scale hydrogen sulfide dispersion, are classified into production well, gas gathering pipeline and pressure vessel. For each type of equipment, the calculation model for the dynamic leakage process is built based on the leakage mechanism and involving the effects of the control system equipped. Then the effectiveness of the control system is assessed on the response to the leakage and the reduction of the total leakage. A simple model is proposed to calculate the gas jet near to the orifice and the results are used as the initial condition for the large-scale gas dispersion.2 Study on highly sour gas dispersion in complex terrainThe model building method of gas dispersion in complex terrain is founded according to the regional characteristics of the gas gathering system in the highly sour gas field, which distributes in the hills of the northeast Sichuan. The numerical model for sour gas dispersion in complex terrain is achieved through terrain retrieval, gas dispersion condition analysis and numerical scheme construction. And in association with the dynamic leakage calculation for the production well, gas gathering pipeline and pressure vessel, the hydrogen sulfide hazard region is predicted and the accident characteristics of the sour gas dispersion is determined for each type of the equipment. The influences on the gas dispersion from the atmospheric conditions and complex terrain are systematically analyzed, and the transportation and distribution of hydrogen sulfide are obtained in complex terrain. Finally, the disadvantages deriving from the dispersed sour gas caused by the leakage of gas gathering system are analyzed in consideration of the complex terrain.3 Analysis of the highly sour gas dispersion in the rainThere are lots of precipitation days and large amount of precipitation over the year in the region where the sour gas gathering system located in China. According to this environment characteristics, the numerical model used for the highly sour gas dispersion under the condition of rain is achieved, which is based on the gas dispersion model and by coupling the simulation of rainfall in large-scale complex terrain with the calculation of mass transfer and chemical equilibrium between the raindrops and dispersed sour gas. The dynamic scavenging rate and cumulative scavenging mass of hydrogen sulfide during the rain are analyzed, and the influences coming from the rainfall intensity, wind speed and complex terrain are evaluated. By comparing the hydrogen sulfide hazard region in the rain with those without the rain, the effects of rain on the control of hydrogen sulfide hazard are obtained. Based on the results, the rain effects on the accident of the sour gas dispersion caused by leakage of the gas gathering system are assessed in consideration of the advantage of hydrogen sulfide scavenging and disadvantage to the accident rescue.4 Assessment on the effctiveness of flaring and venting of the releasing sour gasWith the purpose of assessment on the sulfide dioxide poisoning deriving from the combustion of hydrogen sulfide and the effectiveness in controlling the number of deaths, the study on the flaring and venting of the uncontrolled sour gas release is carried out, which is the most effective control measure to the sour gas gathering system leakage. By analyzing the accident process, the numerical model for the flaring and venting is built including the chemistry analysis involved in the combustion and the gas dispersion simulation of fuel and oxidizer. The conversion efficiency of the hydrogen sulfide into sulfide dioxide through combustion is analyzed. Based on the dose-response relationship for the acute poisoning, the cumulative effect of sulfide dioxide poisoning on the public surrounding the equipments of gas gathering system are assessed. And the hazard region with detailed analysis of its areas, maximal influence distances, and main trajectories are obtained and the distrinution trend in complex terrain is predicted. In theory, the effectiveness of controlling the number of deaths by employing flaring and venting of the leakage of gas gathering system is verified, which can be used to support the accident control and decision making.5 Study on the emergency planning zone for highly sour gas fieldAccording to the absence of determination method of emergency planning zone for gas gathering system in the highly sour gas field in China, the principle of coving the serious hazard zone and providing full protection for the public in case of the accident is proposed to establish the emergency planning zone, and the use of death accident caused by hydrogen sulfide dispersion deriving from the leakage of gas gathering system is suggested to determine the emergency planning zone. The combinations of conditions that result in serious accidents of production well, gas gathering pipeline and pressure vessel are achieved through the analysis of the influence factors of leakage condition, gas dispersion condition, effect of control system and complex terrain. For each type of equipment, the parameters and procedures are proposed to calculate the emergency planning zone. And in combination with the factors influencing the accident rescue, the determination method of emergency planning zone for gas gathering system of the highly sour gas field in complex terrain is provided.6 Development of emergency response system for leakage accident of gas gathering system in highly sour gas fieldThe emergency response system for the leakage accident of gas gathering system in the highly sour gas field is divided into 7 functional modules, which includes rescuer organization, prevention and precaution, emergency response plan, support system, training and drilling, public involvement and document management. Based on incident command system, the rescuer organization is constructed to achieve effective allocation of responsibilities during dynamic accident process. The emergency response plans are classified into overall plan, special plan and onsite action plan. The severity of the accident is classified into 4-level and the corresponding actions are provided to fully and optimally use the resource. The public protection measures under accident are analyzed. According to the characteristics of the protection provided by the shelter-in-place and the safe condition of evacuation, the decision making for public protection is provided.