After the low permeability oil field of Ansai enters the medium and high watercut stage, the main oil reservoir is washed, the production of many wells is low, and the direction of remaining oil digging is unknown. Taking Chang 6 oil layers of Yanchang formation in Wangyao area as the object, on the basis of modern sedimentology, highresolution sequence stratigraphy, basic logging theory and development geology, combining the rock outcrop, sealing core drilling in-spection well and test data, the characteristics of single oil sands scale reservoir heterogeneity, injection and mining connectivity and distribution of residual oil are revealed. The results show that the heterogeneity of single sand bodies has an important influence on the water flooding process of low permeability reservoir, and it also has important inspiration for the division and combination of the development oil layer, the form of well network and the adjustment of water injection. The recovery rate is increased by 4%~6% through comprehensive adjustment as pattern infilling, adjustment of injection-production relation of the single sand body, the precise fracturing and profile control.

In order to explore the new mode of using residual oil, Ansai oilfield first used horizontal wells to encrypt the remaining oil, and 7 key technologies and field tests were carried out. Based on the different way of encryption horizontal well spacing and the transformation parameter study, the mechanism of remaining oil distribution was obtained and the technology of using remaining oil in high and medium water-bearing encrypted horizontal well adapted to Ansai low permeability reservoir was explored. It is proved that horizontal encryption can effectively use the remaining oil and low abundance reservoir between wells to utilize the remaining reserves of developed areas, which provides new enlightenment for the same reservoir to further improve the recovery rate.