冀东油田G76断块在注水开发过程中出现注水井注入压力升高，注水难度增加等问题。为了分析注水过程中储层物性的变化规律，开展了基于二维核磁共振技术的岩心高倍数水驱实验。对目标油藏岩心进行激光粒度测试分析，获得岩心的粒度分布；进行X射线衍射矿物含量分析，获得不同矿物含量占比；开展基于核磁共振技术的高倍数水驱油实验，分析储层物性变化规律。研究结果表明：岩心5-1和岩心6-1分别为含中砂粉砂质细砂岩和含粉砂中砂质细砂岩，其细砂、细粉砂和黏土矿物含量较多。水相相对渗透率及核磁孔隙度随着注水倍数的增加上升到某一高值后呈下降趋势，核磁T₂谱中随着注水倍数的增加，右侧端点值及中、大孔隙对应的曲线左移，二维图谱中自由水信号强度随着注水倍数的不断增加而增加。注入水由束缚水状态至累计注水倍数为500 PV时，束缚水信号不断增加；累计注水倍数为>500~1 000 PV时，岩心5-1的束缚水信号持续增强而岩心6-1的束缚水信号发生减弱。研究认为：注水前期由于黏土矿物发生微弱的水化作用，注水后期因受到水的冲刷，细粉砂粒以及胶结物中的黏土矿物容易脱落运移至喉道处发生堵塞，对孔隙喉道产生一定损害，导致水相渗透率降低。研究成果揭示了中低渗油藏注水井出现注水困难和注水压力增大等问题的原因，对有效降低污染、进一步提升注水开发油藏开发效果提供一定的指导。

In fault block G76 of the Jidong Oilfield, issues such as increased injection pressure and difficulty in water injection have arisen during the waterflooding development process. To analyze the variation in reservoir properties during water injection, high multiple waterflooding experiments were conducted on cores using two-dimensional nuclear magnetic resonance (NMR) technology. Laser particle size analysis was performed on the target reservoir cores to obtain particle size distribution, and X-ray diffraction (XRD) analysis was conducted to determine mineral content proportions. High multiple waterflooding experiments based on NMR technology were carried out to analyze reservoir property variations. The results showed that core 5-1 and core 6-1 consisted of medium sand-bearing silty fine sandstone and silt-bearing medium sandy fine sandstone, respectively, with high contents of fine sand, silt, and clay minerals. The relative permeability of the water phase and NMR porosity initially increased with cumulative water injection to a high value and then declined. In the NMR T₂ spectrum, the right endpoint values and the curves corresponding to medium and large pores shifted left as water injection increased. In the two-dimensional spectra, the free water signal intensity increased with cumulative water injection. As the injected water transitioned from bound water to a cumulative injection of 500 PV, the bound water signal continuously increased. When the cumulative injection is beyond 500 and up to 1 000 PV, the bound water signal of core 5-1 continued to strengthen, while that of core 6-1 weakened. The study suggests that, in the early stages of water injection, weak hydration of clay minerals occurs. In the later stages, due to water flushing, fine silt particles and clay minerals in the cement may detach and migrate to pore throats, causing blockage and damage to the pore throat structure, thereby reducing water phase permeability. The findings reveal the reasons for injection difficulty and increased pressure during waterflooding in medium-low permeability oil reservoirs and provide guidance for mitigating contamination and improving the effectiveness of waterflooding development.