Reservoir Sensitivity Characteristics And Its Influence On Waterflood Development In Xifeng Oilfield

Since 2002,the baima middle area of xifeng oilfield has achieved good development results,but with the continuous development of water injection,the existing problems have become increasingly prominent.As of 2017,the study area has problems such as too high injection pressure and difficulty in injecting water into the formation,resulting in an increase number of under-injector wells and a continuous decline in oil production.Aiming at the problems in the study area,based on the sedimentology,petrology and reservoir protection subject knowledge as the theoretical guidance,on the basis of clear understanding of reservoir geological characteristics,reservoir sensitivity evaluation and mechanism analysis as research focus,combined with the injection water quality in the study area and scale,wettability,such as development characteristics,influence factors of water injection development in the studied area on the analysis of the system.It was found by means of gas permeability measurement,porosity measurement,casting thin section,X-ray diffraction and other experiments or technical means.The average permeability was 1.10×10^-3 m²,and the average porosity was 9.4%.The pores are mainly intergranular pores,followed by dissolution pores,intercrystalline pores and micro-cracks.The main types of pore throats are medium pore,medium thin throat and small pore thin throat.Generally speaking,the reservoir in the study area has poor physical properties and belongs to the ultra-low porosity and ultra-low permeability reservoir.The sensitivity of rock samples was evaluated by carrying out reservoir sensitivity experiments.The results show that the reservoir in the study area has the sensitivity characteristics of weak velocity sensitivity,medium weak water sensitivity,medium salt sensitivity,medium weak acid sensitivity,weak base sensitivity and medium weak stress sensitivity.According to the sensitivity damage mechanism,the existence of various reservoir sensitivities has a certain impact on the increase of water injection pressure in the study area,among which the water/salt sensitivity damage is the strongest.Through the analysis of the ion composition of the water quality in the study area,the results show that the ion composition and salinity of produced water vary greatly and the water type is different after the formation water and injected water are mixed,and it is inferred that the injected water may cause carbonate,sulfate and other scaling after entering the formation.Carry out water quality compatibility experiment,the results show that the formation water and injected water mixture,found that the mixture are different levels of calcium and magnesium ions is reduced,and the number of precipitation.It indicates that the water quality of injected fluid and formation fluid in the study area are not compatible with each other,and scale blockage will occur in the process of water injection.Based on the above research results,it is concluded that geological factors are the fundamental factors affecting waterflood development.Sensitivity damage is the direct factor that affect waterflood development.The water quality and scale formation of injected water are the fluid factors that affect water injection development.Wettability transformation and profile control measures are the development factors affecting waterflood development.