Research Of Plugging Mechanism And Blocking Removal Technology Of SAGD Horizontal Well In Fengcheng Oil Field

Xinjiang fengcheng oilfield is a super heavy oil reservoir,and it has achieved good results since 2008 using SAGD technology.But there are many problems in the process of development.On the one hand,the high density polysulfonate drilling fluid system is easy to cause the formation pollution.The dense mud cake formed by the drilling fluid is easy to block the sieve pipe and the near well zone,which increases the difficulty of processing the circulating preheating liquid.On the other hand,when the SAGD well group is transferred to the production stage,the continuous injection of high temperature and high pressure alkaline steam will cause damage to the reservoir,which will increase the pressure difference between injection and production wells and cause the reservoir and screen pipe to be blocked.Through comprehensive analysis of reservoir sensitivity test.The reservoir rock and scale were analyzed by XRD.And a comprehensive analysis of the change of pH of water.The main reason for reservoir damage is that the steam with high temperature and high pH value is injected into the formation,and the water and rock interaction with stratum minerals occurs,combined with the cementing loose,high permeability,large specific surface area,cause mineral dissolution,transformation and transfer.Finally,due to the changes of temperature,pressure and pH in the near well and the wellbore,the precipitate precipitates and causes the blockage.Analysis of the polysulfonate drilling fluid system and the optimization of indoor mud cake removal experiment.According to whether the site was preheated,it was established that at low temperature,it was oxidized 48 hours at 1% persulphate +1% sodium sulfite solution,and then the system was solved by 4 hours with 13.5% hydrochloric acid +1.5% hydrofluoric acid.At the high temperature,2 hours was oxidized in 1% hypochlorite solution,and then the solution of 2 hours with acid 13.5% hydrochloric acid +1.5% hydrofluoric acid was used.And flow through indoor experiments,the drilling fluid contamination after learning about core plugging evaluation,the results show that through the core flow experiment under low temperature and high temperature mud pollution blockage system for pollution core recovery rate reached 93.58% and 93.58% respectively.According to the results of the whole rock analysis of reservoir minerals and scale samples and the conventional acidification criterion,the acidification system was determined that 13.5% hydrochloric acid +1.5% hydrofluoric acid as the main acid solution block system of the block.The osmotic agent,corrosion inhibitor,cleanup additive and clay stabilizer were selected.And flow through indoor experiments,the recovery rate of the damaged core was 133.43% through the core flow experiment.