Displacement characteristics and development effect of tight oil reservoir: a case from Chang 7 oil layer of the Yanchang Formation in Shangliyuan area, Ordos Basin

In order to study displacement characteristics and development effect of tight oil reservoir, this paper analyzed the sensitivity, fluid percolation and water-driving displacement characteristics of Chang7 oil layer of the Triassic Yanchang Formation in Shangliyuan area, Ordos Basin. The results show that Chang7 oil layer has weak velocity sensitivity, weak acid sensitivity, no water sensitivity and no salt sensitivity. The starting pressure gradient of single-phase flow is up to 2.0 MPa/cm, and negatively correlates with permeability. The saturation of irreducible water and residual oil is high, the oil-water simultaneous vadose region is narrow, and the isoperm point is low, thus the increasing of water saturation can cause the rapidly decreasing of oil phase permeability. According to the changes of WC(water cut)and oil displacement efficiency in different displacement period, the water-driving in the Chang 7 oil layer can be divided into three different periods including no water period, WC-increasing-rapidly period, and high WC period. The oil displacement efficiency in no water period is 18.1%, and the final oil displacement efficiency is as low as 31.7%. In addition, the weak oil wettability of the oil layer will have a profound impact on later waterflooding.