Research On Reservoir Characteristics And Damage Mechanism Of Minghuazhen Formation In QHD32-6 Oilfield

The Bohai bay basin is rich in heavy oil resources,and the efficient development of heavy oil reservoir is of great significance to the production of Bohai oilfield.The reservoir rocks of heavy oil reservoirs are mainly loose sandstone with low degree of cementation and rich in sensitive minerals.The heavy oil has the characteristics of high viscosity and great flow resistance,so the invasion of external fluid and changes in the reservoir environment are easy to cause damage to the reservoir during the development process,which seriously affects the development effect of heavy oil reservoirs.QHD32-6 oilfield is a typical loose sandstone heavy oil reservoir in Bohai bay basin.The main production lay or is the neoneoic Minghuazhen Formation.At present,the oilfield is in the middle and late stage of development.Aiming at the above problems,this paper makes an in-depth study of the lithology,physical properties,pore structure and fluid characteristics of the reservoir in Minghuazhen Formation,and clarifies the main potential damage mechanism of the reservoir in the development process.By combining laboratory experiment and theoretical simulation,the main damage mechanism and damage degree of Minghuazhen Formation in QHD32-6 oilfield were evaluated,providing a basis for efficient development of heavy oil reservoirs.The following results are obtained:(1)The reservoir of Minghuazhen Formation in QHD32-6 oilfield is fluvial facies.The lithology is mainly fine-medium arkose with argillaceous cementation,and primary intergranular pores are dominant.Montmorillonite,isomerite/montmorillonite are the main clay minerals.(2)The reservoir has good pore-throat connectivity,with an average porosity of 35%and an average permeability of 3000mD.It is an extra-high-porosity and extra-high-permeability reservoir.The reservoir pore throat is thick and well connected,class I reservoir accounted for 90%.(3)The reservoir of Minghuazhen Formation is moderately weak to strong kerosene velocity sensitivity,moderately weak formation water velocity sensitivity,moderately weak salt sensitivity,moderately strong to strong water sensitivity,and moderately weak stress sensitivity to weak acid sensitivity.The critical pore velocity was 4.5?11.8m/d,the critical salinity was 3,800?15000mg/L,and the critical stress was 3?5mpa.(4)The non-continuous phases in the oil-water emulsion are mostly in the form of beads with particle sizes ranging from 50?400?m.The emulsion viscosity is the highest when the water-oil ratio reaches 50%.(5)The comprehensive compatibility index of injected water and formation water is 2.44?3.36,which is moderate to severe incompatibility.The incompatibility scale is mainly granular and irregular calcium carbonate particles with particle size of 10?20?m.(6)Lower crude oil viscosity increase rapidly,with the temperature under the condition of lower reservoir temperature 20?,crude oil viscosity can increase 3 times.(7)Main damage mechanisms of Minghuazhen Formation reservoirs in the production process include water sensitivity,particle migration,cold damage,oil-water emulsification,stress sensitivity and incompatibility of fluids with scale formation.Corresponding suggestions on reservoir protection measures are put forward according to the main damage mechanisms.