长7致密砂岩微观孔喉结构测试及特征

以岩心观察、测井、分析试验等资料为基础,探讨了鄂尔多斯盆地湖盆中部长7致密砂岩储层微观孔隙结构测试方法及特征.研究区致密储层以（岩屑）长石砂岩为主,沉积物粒度细,软组分含量高,可见孔面孔率低,多物源沉积造成孔隙结构及成岩作用具有明显差异;储层物性差,孔隙度介于4 ％～10％,平均约为9.12％,90％以上样品渗透率小于0.3× 1 0^-3μm^2介于0.16～0.25× 1 0^-3μm^2研究区裂缝发育;采用高精度扫描电镜、纳米CT等方法结合常规测试,实现致密砂岩储层微米-亚微米-纳米级多尺度孔喉精细识别,采用图像分析法-恒速压汞-高压压汞相结合的方法,建立起了致密砂岩储层孔喉定量化评价方法;测试结果表明：研究区致密砂岩储层微米级孔隙占比约为25％,亚微米级孔隙约为35.9％,纳米级约为30％.储层喉道半径小,孔喉比大,盆地致密储层发育纳米级喉道,主要分布在20～300 nm、配位数较低,孔喉系统复杂,孔喉网络系统由多个独立连通孔喉体构成.孔喉特征参数中最大连通喉道半径、孔喉均值、孔喉分选系数等与物性具有一定相关性,其中最大连通喉道半径与渗透率相关性密切,相关系数为0.918.

Test method and characteristics for micro-pore throat structure of Chang7 tight standstone reservoirs

Based on the studies of predecessors, the characteristics and test methods for pore structure of Chang7 reservoirs in Ordos basin was studied by means of core observation,geophysical logging and other analytic techniques. The study area＇s rock types are mainly consisted of arkose and lithic arkose which characterized by fine sediment grain size, high mica content, low surface porosity of the visible pores and poor physical property. Due to various sediment source, there are significant differences in the reservoirs＇ pore structures and diagenesis. The reservoir physical property of our study areas is poor. The average porosity is 9.12 %（between 4 % to 10% ）and more than 90 % samples＇ permeability is lower than 0.3× 1 0^-3μm^2（between 0.16× 1 0^-3μm^2 to 0.25× 1 0^-3μm^2 ）. The fracture developed very well in study area. Fine identification of multiple size pore throat was implemented efficiently with the combination of high precision SEM test technology, nanometer CT other conventional tests. By using image analysis-constant velocity mercury injectio-high-pressure mercury injection coupling technique, a quantitative evaluation method for pore throat of tight sandstone reservoir was established. The results of the coupling technique show, there are 25 % micron size pore, 35.9 % submicro size pots and 30 % nanometer size pore in study area which is characterized by shortness the throat radius and high pore throat ratio. Nanometer size throat between 20 to 300 nm, low pore throat coordination number, complex pore throat system, the pore throat network is composed of many small internal-linked throat pore network independently. There is better correlation between the reservoir property and the pore throat parameters such as the maximum connected pore throat ratio, the average pore-throat size and pore throat sorting coefficient. The correlation coefficient between the maximum connected pore throat ratio and permeability is 0.918 with markedly correlative.