| The reserves of conglomerate in dongxin plant are about 39.89 million tons,of which the reserves of deep conglomerate reservoir account for 72%,but the recovery rate is only15.6%,which can not reach the average level of the shengli oilfield.The practice of water drive development of adjacent block Yan22(with recovery degree of 6.3% and recovery rate of 20%)shows that this kind of reservoir has strong sensitivity,and it is easy to block the formation in the later stage of water injection.The injection well is often difficult to meet the injection allocation required,which leads to poor water supply capacity of the injection well,and make production wells decline very soon,and unable to meet the benefit level demand under low oil price.In this study,Yan229 in the deep sand conglomerate reservoir in the yanjia area of dongying sag was taken as the representative to study the feasibility of CO2 miscible flooding in this type of reservoir,in order to achieve the development effect of increasing oil recovery rate and increasing oil recovery rate.Firstly,the structural characteristics,reservoir distribution and thickness changes of Yan229 were studied through the geological research.Combined with experimental data,the type of reservoir was defined as mesopore,ultra-low permeability,thin oil and lithologic reservoir.The geological reserves were calculated by volumetric method and simple evaluation was conducted.Then,according to the test and production well datas,the production capacity,energy,water cut,decline and other development indexes of the reservoir development were evaluated.Through the expansion experiment of carbon dioxide,the effect of carbon dioxide on the formation fluid of Yan229 was determined.The minimum miscible pressure is simulated by using long tube,which provides a reasonable basis for the later development.Finally,a theoretical model is established by using numerical simulation technology to study the oil displacement mechanism of carbon dioxide miscible drive,and the design optimization of reservoir engineering is carried out.The study shows that Yan229 is a near-shore underwater fan deposit,and the main material source is from the Yan19 gully,the main oil-bearing phase is the middle fan phase,the oil reservoir type is the mesopore,ultra-low permeability,thin oil,lithologic reservoir,and the geological reserves is 6.76 million tons,belonging to the medium abundance reserves.The reservoir has a high production capacity,but it is affected by the thickness of drilling.The larger the thickness is,the higher the production capacity will be.It has natural energy during development,and can produce by self-injection for a period of time,but it must stand on artificial replenishment energy in the later stage.The water content in the production process is low and there is no obvious upward trend.The decline is in line with the law of exponential decline,which decreases rapidly at the beginning and slow down gradually at the later stage.According to the experimental results of carbon dioxide injection,carbon dioxide has obvious improvement effect on the crude oil in this reservoir,the viscosity of crude oil can be reduced by 70%,and the volume expansion can be up to 1.9 times.The minimum miscibility pressure of 25.9MPa is simulated according to the long tube model.According to the numerical simulation results,carbon dioxide has the top drive effect,and it forms the oil displacement from top to bottom.Therefore,the attention should be paid to the five-point well pattern and the injection-production relationship of top injection and bottom injection in the development process.In order to produce the remaining oil in the low permeability area to the maximum,the periodic injection-production method should be adopted for the development.Finally,according to the economic evaluation,carbon dioxide miscible flooding has obvious advantages in the benefit level than water driving. |
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