Study Of Mechanisms And Technologies To Improve The Effect Of Water-flooding At Super-low Permeability Reservior

At the super-low permeable reservior sandstone of Fu and Yang in Daqing Oilfield, many pore throats exist a lot in the types of compacted and restored flakes and curved lamellas while the pore volume of micropore and the thin, compacted and shrunken throat that contribute little to flow take large scale in the total pore space. Thereof high filtrational resistance is caused by much trouble including high content of reservoir shale, serious sensibility to pressure at waterflooding, remarkable effects of undersaturation and water blocks in micropore. A method with laboratory experiment, theoretical confirmation and field application included was adopted to analyze the non-linear flow characteristics, to reveal the deep mechanism of pinhole enveloping macropore and to provide a new technology of improving the development effect. The outcomes aquired are as follows:Multiple cores with different low and super-low permeability were selected to perform seepage experiments by gas, water and oil. Three fields of flow were observed in the reservoir at different low and super-low core permeability. They are pseudo- elastic flow, transition flow and plastic creep flow. So the concept that there was no correlation of rocky absolute permeability with fluid properties that pasted itself was broken up.Two-phase seepage of water displacing oil in uniform super-low permeability shows that the two-phase seepage zone is narrow. And in this zone, the relative permeability of oil decreases quickly, while the relative permeability of water arises slowly and its value under residual oil saturation is very small(about 20%). Especially, it is found that there exists three types of relative permeability of water such as concave, convex to the water saturation ax and the reversed 'S' pattern.The super-low permeability reservoir is sensitive to pressure, apparent with millipore undersaturation and water blocks. In this study, a new concept of irriducible undersaturation is brought up. And a new mode to describle the process of imbibition dynamics is used to reveal and confirm the mechanism of pinhole enveloping macropore as following: pendular ring of wetting phase (water) gathers→it fills throat→it truncates nonwejting phase (oil ) .The expression of pressure distribution and the equation of oil production are deduced under conditions of non-darcy linear seepage and non-linear seepage. The calculation and analysis with example show that the production rate computed by the law of non-darcy linear seepage is more than the other; at the same producing condition, it is analogous between these tracing ptterns of pressure distribution under two seepage law, but different in rate of change of gradient;According to the behaviours of super-low permeability reservoir, a non-ionic surfactant named Alkanloamide and a microbial surfactant named Bs were developed. It is confirmed by laboratory test and field test that both of them have good effect on unplugging in oil well, decreasing pressure and increasing injection rate in water well, profile control at well group, reservoir sweep, and so on.