基于核磁共振技术储层物性变化规律

Change Law of Reservoir Physical Properties Based on Nuclear Magnetic Resonance Technology

冀东油田经多年的注水开发已经进入特高含水阶段,出现注水压力增大,开发效果差等问题。针对此问题,利用目标岩心分析了黏土矿物含量和粒度分布,结合二维核磁共振技术开展高倍数水洗实验,研究储层物性变化规律及原因。实验结果表明:岩心8-2、岩心16-1分别定义为含中砂质细砂岩、含粉砂中砂质细砂岩,其黏土矿物含量分别为2.41%、2.57%;随着注水倍数的增加,核磁孔隙度表现为先降低后上升的变化规律;随着注水倍数的增加,渗透率(水)波动式变化,前期降低幅度较大,后期出现短暂的上升后持续降低;注水过程中损害主要发生在中、大孔隙且岩心8-2的损害程度要大于岩心16-1;岩心核磁二维谱中自由水的信号变化规律与核磁T_(2)谱中中、大孔隙信号强度变化规律一致。研究认为:注水过程中受到水的冲刷作用,微粒以及胶结物中的黏土矿物容易脱落运移至孔隙喉道处发生堵塞,对孔隙喉道产生一定损害导致渗透率(水)降低,所以注水井出现注水困难和注水压力增大等问题,从而影响油田的开发效果。

After years of water injection development,the Jidong Oilfield has entered a stage of ultra-high water content,with problems such as increased water injection pressure and poor development effectiveness.In response to this issue,The target rock core to analyze the content and particle size distribution of clay minerals,and combines two-dimensional nuclear magnetic resonance technology were used to conduct high magnification water washing experiments to study the changes in reservoir physical properties and their causes.The experimental results show that core 8-2 and core 16-1 are defined as medium sandy fine sandstone and medium sandy fine sandstone with silt,respectively,with clay mineral content of 2.41%and 2.57%.As the water injection ratio increases,the nuclear magnetic porosity exhibits a pattern of first decreasing and then increasing;With the increase of water injection ratio,the permeability(water)fluctuates,with a large decrease in the early stage and a brief increase in the later stage before continuing to decrease.The damage during the water injection process mainly occurs in medium and large pores,and the degree of damage to core 8-2 is greater than that to core 16-1.The signal variation pattern of free water in the 2D nuclear magnetic spectrum of rock core is consistent with the signal intensity variation pattern of medium and large pores in the T_(2)nuclear magnetic spectrum.Research suggests that during the water injection process,particles and clay minerals in the cement are easily washed away and transported to the pore throat,causing blockage and causing certain damage to the pore throat,leading to a decrease in permeability(water).Therefore,water injection wells face difficulties in water injection and an increase in water injection pressure,which affects the development effect of the oilfield.