Research On Formation Characteristics Of Dongying Formation Reservoirs In Jinzhou 9-3 Oilfield And Plugging Mechanism Of Polymer Flooding Reservoirs

Offshore oil and gas resources have great potential,which has an estimated oil resource of 27.53 billion tons and a natural gas resource of 1.06 trillion cubic meters.By the high cost,difficulty and short service life of offshore oil and gas platforms,polymer flooding is often used to improve oil recovery.Jinzhou 9-3 oilfield is one of the earliest polymer flooding test oilfields in bohai sea.At present,the oilfield is in the late stage of development,with high coring cost and large spacing of oil Wells.In addition,due to the complex regional geological characteristics and unclear understanding of reservoir geological characteristics,the production of some Wells in polymer flooding production process is exposed to the rapid decline of oil production,and the expected oil increase effect is not achieved.Meanwhile,problems such as frequent oil well plugging and unclear plugging mechanism also occur.On the basis of depth study of the geological characteristics of Dongying formation,combining with the dynamic characteristics of oil well production capacity and well history analysis,making use of various modern technology testing techniques,By comprehensively studying the internal and external causes of polymer flooding reservoir blockage,the mechanism of polymer flooding reservoir blockage and the causes of productivity decline are clarified,and the basis is provided for preventing the productivity decline of oil Wells and effectively removing the deep blockage,so as to release the productivity of oil Wells affected by polymer flooding.The paper has made the following results and understanding(1)Dongying formation of Jinzhou 9-3 oilfield is formed by deltaic facies deposition,and the reservoir is mainly composed of pebbly medium-coarse sandstone and medium-fine sandstone with interstitials of 4%～18%,clay mineral cementation,and clay mineral dominated by montmorillonite.The reservoir develops primary intergranular pores with good pore connectivity,and is a medium-high porosity and medium-high permeability reservoir.(2)According to the characteristics of oilfield production performance curve,the affected Wells are divided into problem Wells and normal Wells,and the judgment and identification marks of different types of Wells are established;Through the reservoir comparison of different types of Wells,it is found that the decline of production of some of the problem Wells is related to the poor quality of the reservoir itself.The workover site operation and well history data show that the decline of the production of the problem well is related to the plug produced by the affected well.(3)The flow chart of downhole plugging analysis was established,and the systematic analysis of downhole plugging was carried out.The study showed that the components of downhole plugging were organic matter,inorganic matter,water-soluble polymer,oil,etc.The main components of inorganic are quartz,iron salt,calcium salt,fluorosilicate,fluoroaluminate,etc.The organics are insoluble or flocculated polymers and the main structure is partially hydrolyzed dilute amide.The molecular weight of water-soluble polymer is less than 10,000,which is 99%lower than that of the produced polymer.(4)Through the analysis of the formation mechanism of blockage,simulation experiments,the damage mechanism of polymer flooding reservoir was clarified,includings:① Polymer retention damage is one of the main factors of reservoir blockage;② In acidizing stimulation operations,residual acid reacts with formation minerals to produce high-priced cations,such as aluminum and iron,which combine with the polymer produced by oil Wells to form organic micelles.Such micelles will quickly block the pore throat,resulting in short acidizing aging and rapid decline in productivity.③ Acid fluid and reservoir mineral incompatibility in acidizing stimulation operation produces secondary precipitation,and these in organic scales become the core of the plug,interwoven with the polymer,aggravating the degree of reservoir plugging.④Through the sensitivity experiment results show that,because of the reservoir layer heterogeneity is strong,the liquid profile is uneven,the reservoir has a certain degree of velocity sensitivity damage.