Study On Remaining Oil Droplet Dynamic Conditions And Water Flood Efficiency Changing Mechanisms In The Ultra-high Water Cut Period

When entering the ultra high water cut period, the distribution and size of the remaining oil have been greatly changed. In ultra high water cut oilfield development, the problems, such as what is the moving characteristic of the remaining oil in micro pore structure, what is the dynamic condition of the moving remaining oil, how water flood efficiency changes, etc., play a new and core role and become unavoidable. Study on remaining oil droplet dynamic conditions and water flood efficiency changing mechanisms in the ultra-high water cut period is meaningful to improve economic efficiency and keep stable and high production of oil field.Firstly, influencing factors of remaining oil droplet micro-force status in ultra-high water cut period have been investigated. Study shows the main forces of remaining oil droplet in pore network structure are buoyancy, gravity, capillary force, injection pressure, the frictional resistance force of the rock, viscous force, the resistance force of Jamin effect, etc.; the influences of pore structure related parameters (study status of pore structure, classification and analysis of pore structure models, influences of pore structure on remaining oil force state, force difference in different pore structure) on the micro force status of remaining oil droplet have been qualitatively analyzed; the influences of different reservoir types (low angle pore structure oil reservoir, high angle pore structure oil reservoir, oil reservoir with positive rhythm and anti-rhythmic oil reservoir) on the micro force status of remaining oil droplet have been studied;Secondly, remaining oil distribution characteristics in different water cut period have been compared and analyzed, including typical characteristics of remaining oil distribution in low-middle water cut stage, high water cut stage and ultra high water cut stage.Thirdly, according to the micro forces analysis of remaining oil droplet and establishment of mathematical models, dynamic conditions of moving remaining oil droplet in ultra high water cut stage have been proposed, including micro force status of remaining oil droplet in three different types of pore structure models; establishment of micro force status equation of remaining oil droplet in simplified pore structures; description of moving status of remaining oil droplet in three different types of pore structure models; capillary selecting mechanism of remaining oil droplet in different reservoir types and simplified pore structures; dynamic conditions and Threshold conditions of moving oil droplet in three simplified pore structures-parallel, variable cross-section and pore network capillary model.Fourthly, indoor experiments have been running to study the limited water flood efficiency in ultra high water cut period, including experimental design, purpose, content and process; running water flooding experiment and relative permeability experiments; processing and analysis of the experimental data with transient method. Remaining oil saturation during ultra high water cut stage has been studied, including comparisons of present calculation methods of remaining oil saturation; study of remaining oil saturation distribution pattern from the perspective of seepage and establishment of remaining oil saturation distribution equation with time and place change; study of remaining oil saturation distribution adapted to ultra high water cut stage from the perspectives micro parameters and establishment of remaining oil saturation distribution equation with micro parameters like capillary radius and maximum capillary radius change.Fifthly, predicting methods of water flood efficiency in ultra high water cut stage have been studied from different perspectives:internal and external influencing factors of water flood efficiency in ultra high water cut stage have been studied; present oil displacement efficiency predicting methods, including Water drive characteristic curve method, Empirical formula method, Decline curve method and Cash flow method, have been investigated; four kinds of new water flood efficiency predicting methods in ultra high water cut stage based on new type of water drive characteristic curve, material balance equation, and GM(l,n) and ANN functional simulation separately have been discussed in-depth.Sixthly, changing mechanisms of water flood efficiency in ultra high water cut period have been studied. For one thing, studying of changing mechanisms of water flood efficiency in ultra high water cut period from the perspective of reservoir engineering; for another, studying of changing mechanisms of water flood efficiency in ultra high water cut period from the perspective of experiments and numerical simulations, such as Newton interpolation principle and GM (1, n)-Neural network model.