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To fulfill the demand increase for oil, is it better to actively seek and develop high cost resources such as tight, deep-water, and polar-region reservoirs, or to enhance development of mature fields? Especially in low-oil-price period, is it more economical and less risky to take efficiency EOR to recover mature fields? The paper conducted studies on it by analyzing technical and economical effect of applying a new type of polymer flooding technology on 8 reservoirs. The paper made statistics of the technical and economical effect of applying a new micro-nano particle-type polymer flooding method on 8 reservoirs with different conditions, which were reservoir temperature from 24 to 126 °C, crude oil viscosity from 1.36 to 156 mPa·s, salinity from 4212 to 200,000 mg/L, waterflooding phase water cut from 81.4% to 97.5%, and waterflooding phase recovery degree from 9.55% to 64.4%. And based on the statistics, a numerical simulation model and economic analysis model were built up. The economical competency of the technology was calculated and analyzed under different oil price. The statistics showed that all the 8 projects of the new polymer flooding obtained good technical and economic effect. Even though using the oil price of 30 USD/bbl to make calculation, the input to output ratio of the 8 projects is between 1:1.0 and 1:9.04. The studies on the numerical simulation model and economic analysis model illustrated that it was economically feasible to use this type of EOR method to develop mature fields when oil price was under 30 USD/bbl. Through conversion, the investment of using this EOR method to develop mature fields for 1 million tons of productivity was 488.7 million USD, while the investment of developing conventional new area and untouched tight shale oil reservoir for the same productivity was 900-1100 million USD and higher than 1500 million USD. Since there was lack of deep water field and polar region field development data, they were not able to be compared. Using efficient EOR method to develop mature oil fields can rejuvenate numerous conventional oil resources, and it need not spending heavy exploration investment. Under low oil price condition, it is obviously more economical to use EOR technology. The opinion of the paper may provide some reference for oil companies to make investment decision in low oil price period.

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In the last few years horizontal wells are becoming increasingly important. This paper presents a hydrodynamic method for solving the flow problem of areal water-flooding systems of combinations of vertical and horizontal wells(5-spot well pattern and 7-spot well pattern). The potential function, production rate, breakthrough time, areal sweep efficiency and stream functions are derived respectively. Also, the flow resistance method is used for getting the equations of horizontal well production for all the areal floods. Finally, the equations of oil productions derived by the two methods are compared. Introduction Horizontal wells have become a subject of renewed interest and played an increasing role as alternate production tools to vertical or slanted wells over the last ten years. But most of them are individual and the study on the fluid flow of horizontal wells is under the limitation of individual well unlike vertical multi-well systems. In order to make a proper use of horizontal wells in oil and gas production, how to combine horizontal well with another horizontal well or vertical wells is becoming increasingly important. This paper presents a hydrodynamic method for solving the fluid flow problem of areal waterflooding systems of combination of vertical and horizontal wells(5-spot well pattern and 7-spot well pattern), which is of importance for reservoir engineering study of horizontal well development. P. 445