Study On Advanced Treatment Process Of Produced Water In PuGuang Gas Field And Recycling Technology

With the increasing global demand for natural gas,the production of natural gas has gradually increased,and the produced-water has gradually increased.Generally,a large amount of oil,soluble salts,suspended matter,bacteria and other components are dissolved in the produced water.If the produced-water is not treated,it will cause serious environmental pollution.In order to protect the environment and effectively prevent pollution,the gas field water must be fully and effectively treated.This thesis takes the Pu Guang gas field in Sichuan as an example.Through the prediction and analysis of the produced water volume,the current status of the sewage treatment system and the reinjection capacity of the water injection system,there will be a notch about 1107m³/d in 2019.Therefore,the contradiction between the increase of the produced water volume and the decline of the reinjection capacity is prominent.Analysis on the necessity and feasibility of increasing the water injection capacity by restoring the capacity of water injection wells,newly re-injecting wells,and converting exploration wells back to injection wells,it is proposed that the produced-water be further processed and then recycled into natural purification plant in Puguang.Based on the existing research of domestic and international gas-field produced water utilization,this paper did a targeted research.Combining the water quality indicators of the produced water and the requirements of the water quality indicators of the reused water,this paper raised process flow to achieve recycling,which has the characteristics of stable and efficient,simple operation,and low treatment cost etcThrough intensive research,the obtained results are:(1)The water produced in the Puguang Gas Field is mainly condensate water and formation water produced from natural gas wells.In addition,corrosion inhibitor and foam scrubbing agent for auxiliary production was added during gas exploitation and gathering.Therefore,the produced water is a complex water sample,which mainly manifested as p H values between 6 and 8,TDS content of 20,000 mg/L,COD content of 3000 mg/L,calcium and magnesium scale ion content of 1400 mg/L,and NH₃-N content.of 150 mg/L and sulfide content of 3500 mg/L.(2)Analysis on the geological conditions of the terrestrial and marine strata in Puguang area,combined with the dynamic monitoring analysis of produced-water reinjection,which make it unfeasible to be increased water by newly re-injecting wells or converting exploration wells back to injection wells(3)Through the comparative analysis of the re-injection of produced water and resource reuse,the produced water will be used as the circulating cooling water,which not only requires water supply for the purification plant,but also meets the requirements of relevant standards in environmental protection departments.Therefore,adopting a resource utilization method is an effective way to resolve the contradiction between the increase in water output from gas fields and the decline in reinjection capacity.(4)According to the water quality index data of the produced water in Puguang Gas Field,the wastewater needs to undergo coagulation,sedimentation and filtration to remove 80%of calcium and magnesium ions,95%of suspended matter,and 98%of NH₃-N by stripping process.The multi-effect evaporation process removes 98%of the COD and 99%of the chloride ions.The whole process realized the recovery,which meets the requirements of the circulating cooling water of Puguang Natural Gas Purification Plant.(5)In the advanced treatment stages of NH₃-N removal,COD removal,and desalination of produced water from gas fields,the technology of"stripping distillation pre-evaporation+low temperature multi-effect evaporation"was integrated and developed,so that the water quality standard reached the Sinopec standard"Water Management Technical Requirements Part 2:Recycled Water(Q/SH 0628.2-2014).