Research On Reservoir Characteristics Of Dongying Formation In LD5-2 Oilfield And Reservoir Protection Technology During Workover

China's heavy oil resource is abundant,widely distributed in Bohai bay,Songliao,Junggar basin.The rock types of heavy oil reservoirs are generally loose sandstone,with loose cementation,high sensitive mineral content,high porosity and high permeability.Meanwhile,heavy oil has the characteristics of high viscosity and large flow resistance,and is easy to be damaged in the development process.Through the elaborate characterization of reservoir characteristics,laboratory experiments are used to clarify the mechanism of heavy oil reservoir damage and carry out targeted reservoir protection measures,which is of great significance for the efficient development of heavy oil reservoirs.LD5-2 oilfield is a typical loose sandstone heavy oil reservoir in Bohai bay basin.In the development process,there are problems such as unclear understanding of geological characteristics,insufficient research on reservoir damage mechanism,and great disparitie in productivity recovery degree after workover,which seriously affect the efficient development of oilfield.Aiming at the above problems,this paper systematically studies the lithology,physical property,pore structure,fluid and other characteristics of Dongying formation reservoir in LD5-2 oil field by various analysis and test means and indoor simulation experiment evaluation,and classifies the reservoir on this basis.The main damage mechanism and damage degree of reservoir in the workover process are defined,and the research on the protection technology of reservoir in workover is carried out.The specific research results are as follows:(1)The reservoir of Dongying formation of LD5-2 oilfield is a delta front subfacies,and the rock type is mainly medium-coarse feldspar lithic sandstone with loose cementation.The average interstitial content was 7.8%,mainly argillaceous,and the clay mineral types were mainly montmorillonite,followed by illite and kaolinite.(2)Dongying formation has good physical properties.The average porosity and average permeability of the upper Dongying second section are 31.3%and 5417mD respectively.The average porosity and permeability of the lower Dongying second section are 30.5%and 1571mD respectively.(3)the reservoir space of Dongying formation mainly consists of intergranular pores,with large pore and good connectivity of reservoir pore throat.The average pore throat radius is 8.3-27.4?m,and the mainstream throat radius is 19.6-37.8?m.Dongying group mainly type ? reservoir,accounted for 83%.(4)the reservoir in Dongying formation is weak to moderately strong water-sensitive,weak to moderately strong speed-sensitive,with a critical salinity of 7500mg/L.and the critical velocity is 0.25-1.5ml/min.In the workover process of Dongying formation,the damage mechanism mainly includes velocity sensitivity,water sensitivity,cold damage and oil-water emulsification.(5)aiming at the main reservoir damage mechanism in the workover process and based on the reservoir protection principle of "one well and one policy",the low-damage workover fluid system suitable for Dongying formation of LD5-2 oilfield was optimized.The dynamic simulation experiment showed that the permeability recovery degree of the optimized workover fluid system was>90%and the reservoir protection effect was good.