Experimental Study on Oil Recovery of Tight Oil Reservoirs in Different Oil Occurrence States

The occurrence state of crude oil in tight reservoirs is complex and is significantly influenced by different development methods. In this paper, first, a core-scale static imbibition/dynamic huff and puff and frozen slice residual oil joint testing experimental technology is developed. Second, fluorescence images of tight reservoir cores in different states are tested using the laser confocal method under different conditions. Third, the amounts of crude oil in different occurrence states are quantitatively identified. The results show the following: (a) Under static imbibition conditions, pressurization will increase the recovery of free-state crude oil, reduce the recovery of semibound-state crude oil, and increase the recovery of bound-state crude oil. (b) Under static imbibition conditions, both imbibition systems will use a large amount of free-state crude oil, a small amount of semibound-state crude oil, and a very small amount of bound-state crude oil. The ability of PAM-type slick water system to utilize free crude oil is stronger than that of anionic nonionic surfactants. The ability to use semibound-state and bound-state crude oil is weaker than that of the anionic nonionic surfactant system. (c) Increasing soaking time under dynamic huff and puff conditions will increase the recovery of free-state crude oil and reduce the recovery of semibound-state and bound-state crude oil. (d) The ability of static imbibition to utilize free-state crude oil is stronger than that of dynamic huff and puff. The ability of static imbibition to produce semibound-state crude oil is weaker than that of dynamic huff and puff. The capacity of producing bound-state crude oil is the same as that of dynamic huff and puff.