Study On Pore Structure And Seepage Characteristics Of Reservoir In Ultra-low Permeability Fuyu Reservoir Of Daqing Oilfield

In this paper,the low-permeability oilfield of Fuyuite in block AQ76 is studied,and the combination of lithology analysis,casting thin section,conventional mercury intrusion,nuclear magnetic resonance,starting pressure gradient,wettability,and seepage and oil displacement experiments are used.From qualitative analysis to quantitative characterization,from the macroscopic experiment to the microscopic mechanism,the characteristics of the microscopic pore structure,the single-phase seepage mechanism,and the oil-water two-phase percolation characteristics of ultra-low permeability reservoirs are systematically described.Research indicates:1.The overall performance of the Fuyu oil layer is characterized by low porosity and ultra-low permeability reservoirs.In semi-logarithmic coordinates,the porosity and permeability of the core of the Fuyu oil layer have a good linear relationship.The rock skeletons of the Fuyu oil layer in the Xing76 block are mainly composed of quartz,amasite,plagioclase and calcite,and contain a small amount of iron mineral components;the susceptibility to rapid-sensing,water-sensitive,acid-sensitive and alkali-sensitive hazards,and the tendency to hydrophilicity.The main feature of the Fuyu oil layer in the Block A76 is fine sand siltstone and feldspar lithic sandstone;the maximum grain size range is(0.24-0.56)mm,and the main grain size range is(0.04-0.40)mm,and the permeability The increase in the maximum particle size and the main particle size range showed an increasing trend.2.The discharge pressure of Fuyu oil layer increases with the decrease of permeability.When the permeability is less than 1×10-3?m2,it shows a sharp upward trend,indicating that the reservoir has a large starting pressure gradient and is difficult to start.3.Analyze the pressure gradient and critical initial permeability of the well displacement in the Fuyu oil layer of the Block A76 and draw the conclusion that the injection pressure and the pressure gradient and the starting pressure gradient are large.The critical start-up permeability is small,the utilization of the reservoirs in the near-wellbore region is good,the production and operation mechanism is relatively reasonable,and most of the reservoirs can be effectively used.4.The relative permeability of the water in the Fuyu oil layer of the Block A76 rose rapidly in the early period and it was a straight-to-convex curve.The relative permeability of the residual oil was low,and the relative permeability of the oil phase decreased rapidly,indicating that the reservoir water injection It is difficult to develop;irreducible water saturation and residual oil saturation are high,indicating that the reservoir is hydrophilic.5.The Fuyu oil layer of the Block A76 is mainly characterized by a strong water-wetting reservoir;the seepage recovery is related to the water wetness intensity,and increases with the increase of the wetness index;the rock samples with the same conditions do not have water saturation.At the same time,the infiltration capacity and the infiltration rate are different.As the water saturation of the core increases,both the permeability recovery and the infiltration rate show a downward trend.The cores of different degrees of water wetting increase the water saturation and bind water.Compared with the results of the seepage under the conditions,both the seepage recovery and the infiltration rate decrease with the increase of the water saturation,but the decrease range is different,the weaker the degree of water wetting,the greater the decrease;The yield increased slightly with the increase of pressure in the infiltration formation;under the same pressure increase condition,the recovery rate of the recovery increased with the increase of the reservoir water wetting strength.