Waterflooding experiments were conducted in micro-models (microscopic scale) and on plunger cores from low permeability, extra-low permeability and ultra-low permeability reservoirs in the Ordos Basin under different displacement pressures using the NMR techniques to find out pore-scale oil occurrence state, oil production characteristics and residual oil distribution during the process of waterflooding and analyze the effect of pore structure and displacement pressure on waterflooding efficiency. Under bound water condition, crude oil mainly occurs in medium and large pores in the low-permeability sample, while small pores and medium pores are the main distribution space of crude oil in extra-low permeability and ultra-low permeability samples. During the waterflooding, crude oil in the medium and large pores of the three types of samples are preferentially produced. With the decrease of permeability of the samples, the waterflooding front sequentially shows uniform displacement, network displacement and finger displacement, and correspondingly the oil recovery factors decrease successively. After waterflooding, the residual oil in low-permeability samples is mainly distributed in medium pores, and appears in membranous and angular dispersed phase; but that in the extra-low and ultra-low permeability samples is mainly distributed in small pores, and appears in continuous phase formed by a bypass flow and dispersed phase. The low-permeability samples have higher and stable oil displacement efficiency, while the oil displacement efficiency of the extra-low permeability and ultra-low permeability samples is lower, but increases to a certain extent with the increase of displacement pressure.

对鄂尔多斯盆地不同驱替压力下的低渗、特低渗和特低渗油藏柱塞岩心进行微观模型（微观尺度）注水实验，利用核磁共振技术找出孔隙尺度油藏分析注水过程中的状态、采油特征和剩余油分布，分析孔隙结构和驱替压力对注水效率的影响。在束缚水条件下，原油主要存在于低渗透样品中的中、大孔隙中，而小孔和中孔是特低渗透和超低渗透样品中原油的主要分布空间。在注水期间，三类样品中大孔原油优先产出。随着样品渗透率的降低，水驱前缘依次呈现均匀驱替、网状驱替和指状驱替，相应的采收率依次降低。水驱后低渗透样品中的残余油主要分布在中等孔隙中，以膜状和角状分散相出现；而在特低渗和超低渗样品中，则主要分布在小孔隙中，并以旁路流和分散相形成的连续相出现。低渗透样品具有较高且稳定的驱油效率，而特低渗透和超低渗透样品的驱油效率较低，