Research On Seismic Difference Detection Of CO₂ Flooding

CO₂ flooding is an important technology to improve recovery ratio,the development of CO₂ flooding has been more mature abroad.The studies of CO₂ flooding are also carried out in our country in recent years.On the whole,CO₂ flooding can improve recovery ratio effectively,especially those reservoirs in later development stage and reservoirs with low permeability.At the same time,Carbon sequestration becomes an international hotspot issue with international increasing concern over the carbon emissions.And geophysicists paid more and more attention to the seismic dynamic monitoring of CO₂ flooding.Although CO₂ flooding technology is applied in many big oilfields in our country,the technology is still limited to the detection of injection-production process of CO₂ flooding.And how to combine the geophysical technology to monitor the oil and gas migration,determine the remaining oil distribution is still a problem.Geophysical technology has the important status in the CO₂ flooding technology,it also takes the role of observation,monitoring and proving.At present,domestic researchers carry out exploratory study about logging,interwell tracer,well test,water flooding and oil and gas properties test for CO₂flooding monitoring.Utilizing seismic data to carry out the displacement monitoring is one of the important development trends of CO₂ flooding,but we not yet conducted the study about that before.Research on seismic difference detection of CO₂ flooding is regarded as the important content of seismic dynamic monitoring,but few researchers do some related research about that.In this paper,we carried out research on seismic difference detection of CO₂ flooding based on the data before and after CO₂ injection.G89-1 well block is CO₂ miscible flooding pilot area of shengli oil field and it is located at the middle of Jinjia-Zhenglizhuang-Fanjia nose-like structure of boxing subsag of Dongying sag.Seismic data acquisition completed in1992 and 2011.CO₂ injection experiment completed in the period 2008-2010,seismic data before and after CO₂ injection can be used to the research on seismic difference detection of CO₂ flooding.First,we conduct the comparative analysis about the difference of seismic data before and after CO₂ injection,and analyze the seismic data from the observation system,time difference,amplitude,frequency spectrum.Then,we use well seismic data for further analysis,and conduct forward modeling according to the actual seismic profiles across the known wells.CO₂ injection can caused the frequency anomaly,so it's necessary to extract frequency-class attribute before and after CO₂ injection,and results show that single-frequency attributes,spectrum area difference and frequency band percentage etc.is sensitive to the difference detection before and after CO₂ injection.We also do the exploratory research on CO₂ gas channeling phenomenon,the methods include seismic fractures detection,logging data analysis and the actual investigation of work area etc.,and we get the conclusion by comprehensive analysis of all these.Finally,we compare the seismic data before and after CO₂ injection based on frequency-dependent velocity factor,it has remarkable effects and demonstrates the effectiveness of frequency-dependent velocity factors for the difference detection of CO₂ injection.