Research On The Variation Law Of Sandstone Reservoir After Water Flooding In QHD32-6 And SZ36-1 Oilfields

Both QHD32-6 and SZ36-1 oilfields had experienced long-term water flooding in Bohai Sea,and the conflicts between layers were obvious.Based on the experimental data of closed coring Wells in two oilfields,and combined with drilling,logging and dynamic data,the variation law and mechanism of reservoir parameters before and after water flooding were studied,which provided a reference for comprehensive adjustment research of oilfields.This thesis studies the variation law of reservoir lithology,physical properties,pore structure,wettability,electrical properties and seepage characteristics after the water flooding in QHD32-6 and SZ36-1 oil field.With the increase of water flooding degree,the median grain size,the porosity,the permeability,the average radius of the pore throat and the oil displacement efficiency had all increased.The mud content,the displacement pressure and the resistance had all decreased.The phase permeability curve shifts towards the hydrophilic direction.Moreover,the variation of various parameters had been compared semi-quantitatively according to different flow units.The variation of most parameters of flow unit 1 is the largest,followed by flow units 2 and the minimum of flow units 3.The controlling factors and changing mechanisms had been discussed in this thesis about reservoir lithology,physical property,electrical property and seepage characteristic parameters before and after water flooding.The main factors causing the changes of lithologic parameters were particle migration of sandstone,hydration of clay minerals,sedimentary microfacies and diagenesis.The migration of sandstone particles mainly resulted in the increase of median grain size and the enhancement of reservoir heterogeneity.The hydration of clay minerals mainly resulted in the decrease of argillaceous content.Sedimentary microfacies with good physical properties were strongly transformed by water flooding.In the early diagenesis,compaction was weak.Mineral particles were mainly in point contact and easily transported by injected water.The changes of lithologic parameters were also the main reason for the changes of pore structure parameters and physical parameters.With the development of water flooding,the average pore radius increased,the displacement pressure decreased,the clay mineral content decreased,and the permeability increased.The main factors that caused the changes of electrical parameters were reservoir wettability and formation of main flow network in high water-cut stage.The value of saturation index n decreased with the increasing of rock hydrophilicity.When the reservoir water saturation increased to a certain extent,the flow network composed of large pores in the rock begined to form and remain stable,and the trend of resistivity increasing coefficient changed slowly.The main factors that caused the change of reservoir seepage characteristics were the changes of reservoir pore structure and wettability.The oil displacement efficiency increased when the average coefficient of pore structure increased.With the increasing of water flooding degree,reservoir hydrophilicity,oil displacement efficiency and oil phase permeability increased.