东风港油田特低渗透油藏微观孔隙结构及渗流特征试验研究

为了经济有效地开发东风港油田特低渗透油藏，对其储层的微观孔隙结构及渗流特征进行了试验研究。以沙四段上段为例，选取具有代表性的4块岩心，利用恒速压汞仪器，分别获得了其喉道半径、孔隙半径、孔喉半径比和毛管压力的分布特征；在70 ℃条件下，采用非稳态法分别对4块岩心进行水驱油相渗试验，获得了特低渗透储层的渗流特征。试验得出，喉道半径分布范围越宽峰值越大，孔隙半径分布差别不明显，孔隙半径比因渗透率不同而不同，特低渗透岩心排驱压力大，最大连通喉道半径比较小，储层开采难度相对较大；该储层平均束缚水饱和度相对较高，随着渗透率的升高，两相共渗区跨度逐渐减小。研究结果表明，驱油效率和渗透率高低相关性差；正常型相对渗透率曲线对应的多是孔喉半径比较大、连通性较差的储层，而直线型相对渗透率曲线对应的则是孔喉半径比相对较小、孔隙连通性较好的储层。因此，厘清微观孔隙结构对于合理制定开发方案具有指导意义。 

Experimental Study on Micro-Pore Structure and Seepage Characteristics of Ultra-Low Permeability Reservoirs in the Dongfenggang Oilfield

In order to achieve cost-effective development of the ultra-low permeability reservoirs in Dongfenggang Oilfield, micro-pore structure and seepage characteristics of the reservoirs were studied. Taking the upper section of Es4 Formation as an example, detailed pore structure properties such as throat radius, pore radius, ratio of pore radius to throat radius and capillary pressure distribution were obtained through constant speed mercury injection. Then, the seepage characteristic properties of the ultra-low permeability reservoirs were acquired from relative permeability experiments of water displacing oil with the unsteady state technique of core samples under 70 ℃. Experiments showed that the larger the throat radius distribution range is, the larger the peak value would be and that pore radius distribution presented no significant difference; in fact, pore to throat radius ratio depends on the permeability and the displacement pressure is very high for cores with ultra-low permeability due to their very small radius of connected throats. Thus it is challenging to produce ultra-low permeability reservoirs. In addition, the average irreducible water saturation of the reservoir is high, which would result in oil-water two phase flow area reduction as permeability increase. The results of the experimental study indicated that there is no strong correlation between the oil displacement efficiency and permeability. Most of normal water phase relative permeability curves fit reservoirs with large throat radius and poor connectivity. In contrast, the linear type water phase relative permeability curves fit reservoirs with small throat radius but good connectivity. Therefore, it is of great significance to reveal the micro pore structure in order to create the best possible development strategy.