In order to study the influence of the scale effects on the oil displacement efficiency of natural gas miscible-flooding

we proposed to take the volatile reservoir with mid-low permeability of the third section of the Shahejie formation of some block in Zhongyuan oilfield as an example

and carried out the small scaled physical simulation experiment of natural gas flooding by the combination of natural cores with different length to revealed the mechanism of enhanced oil recovery by long core miscible flooding. And then we researched the gas driving development effects with large size by the numerical simulation method based on the actual geological model. The results show that the recovery rate of the natural gas recovery with the core length of 1 800 mm

950 mm and 500 mm respectively are 90.88 %

82.89 % and 64.8 %. It is found that the oil displacement efficiency of the long core is about 25 % higher than that of the short one

that is to say

along with the increase of the injection volume at the same injection rate

the miscible section of the long core is longer

the miscible contact is sufficient and there are time lags in gas breakthrough. Meanwhile

it is verified by numerical simulation that the best well spacing range is 300 ~ 350 m. Within this range

the larger the well spacing is

the better the displacement effect will be. But as the well spacing increases

the increasing degree of the recovery efficiency and the economic effect all get worse. Based on this study

the influence of size effect on natural gas displacement is further clarified

which is of great practical significance for the optimization of injection and production parameters and the development of similar reservoirs.