Study of High-sulfur Natural Gas Field Water Treatment

Abstract High-sulfide gas field water with more than 100mg/L hydrogen sulfide account for 54.5% of gas wells in the Southern and Eastern gas fields of Sichuan, China. Because an effective method of High-Sulfide Natural Gas Field Water (HSNGFW) treatment has not been found, pollution problems related to HSNGFW remain, In recent years, systematic research on treatment technology for HSNGFW has been accomplished, and stripping-coagulation sedimentation process has been selected. In light of economic factors, air stripping is first used to treat HSNGFW. This results in the sulfide content dropping from several hundred to less than 100 mg/L when optimum treatment parameters are used. Then, ferric chloride, polyaluminium chloride (PAC) and newly developed SW-I are utilized for the further coagulation sedimentation. There procedures further lower sulfide content to less than 1 mg/L. Moreover, the treated water does not become yellow even if excessive ferric chloride is used. Field applications show that the results obtained generalize to in vivo settings. Introduction Gas-field water is formation water which is simultaneously brought to the surface when natural gas is produced. Because gas-field water is in contact with high-sulfide natural gas for a long time before the gas field is developed, it sulfide content is very high. Based on statistical data, the average value and maximum value of its sulfide content are 387.0 and 962.0 mg/L respectively in the Eastern gas field of Sichuan. The average value and maximum value of sulfide content are 177.2 and 763.5 mg/L respectively in the Southern gas field of Sichuan. Because gas-field water contains high sulfide and large quantities of it are produced (Sichuan gas field produces 2.0 X 106 m3 gas field water), severe pollution problems will result if the water isn't treated carefully. A great many research projects that attempting to resolve HSNGFW's polluting problem have been accomplish for many years by institutes of the Sichuan Petroleum Administrate Bureau. The main method which has been used to treat gas field water is an oxidization process. It is difficult for this process to treat gas field water in which sulfide contents are more than 80 mg/L, so our institute has cooperated with Eastern Development Company of Sichuan, and Southern Gas Field of Sichuan in studying HSNGFW's treatment technology. Systematic research has been done and stripping-coagulation sedimentation process has been selected as the treatment of choice. Treatment results aresatisfactory by laboratory test and field application. This paper discusses key experimental results. EXPERIMENT OF RESEARCH The stripping-coagulation sedimentation process is used to treat HSNGFW. First, the wastewater is sent to a sieve-plate stripping tower and contacts adverse air currents in the tower. Air is utilized to reduce the partial pressure of hydrogen sulfide in the upper area of the water, thus making hydrogen sulfide rapidly separated from the water. Then, treated water enters the coagulation reaction unit, and clear water is obtained by the coagulation sedimentation process. The orthogonal device method is used to select the parameters of the stripping process as well as types and amounts of coagulant and decoloration-coagulant aid.