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黏土矿物在鄂尔多斯盆地姬塬地区长6段各小层中均有分布,是该区致密砂岩储层中主要的填隙物,对储层物性有重要的影响。利用铸体薄片、压汞、扫描电镜(SEM)、X-射线衍射(XRD)等实验测试技术,分析储层岩石学特征认为,长6段是以长石岩屑砂岩和岩屑长石砂岩为主的低孔低渗的致密储层,其平均孔隙度为7.78%~9.13%,平均渗透率为(0.20~0.34)×10-3μm2。重点分析黏土矿物与储层物性之间的关系认为,高岭石和绿泥石是长6储层中主要的黏土矿物,对储层物性的影响较为复杂。少量的高岭石和绿泥石往往预示着储层孔隙度较好,而过量的高岭石(绝对含量>7%)和绿泥石(绝对含量>10%)则会大大降低储层的孔隙度。通过计算,长6储层原始孔隙度为41.13%~42.04%,高岭石充填导致砂岩孔隙度降低4.52%~4.78%,其损失率为10.74%~11.38%;绿泥石对长6段砂岩孔隙度的影响仅次于高岭石,导致孔隙度降低4.12%~4.70%,其损失率为9.81%~11.18%。自生高岭石对砂岩渗透率有一定的建设性作用,而绿泥石则导致砂岩渗透率降低。长6储层中伊利石含量较高岭石和绿泥石含量低,但由于其主要以丝缕状呈搭桥式充填孔隙,导致孔隙度和渗透率均有所降低,其孔隙度降低1.33%~2.08%,损失率为3.17%~4.94%。因此,在姬塬地区长6段致密储层中,黏土矿物对孔隙度的影响程度为:高岭石>绿泥石>伊利石。
Clay minerals are distributed in all layers of Chang 6 Member in Jiyuan area, Ordos Basin. They are the main interstitial material in tight sandstone reservoirs in this area, and have an important influence on reservoir physical properties. The laboratory petrology of castings, mercury intrusion, scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the petrological characteristics of the reservoirs. The Chang 6 Member is composed of feldspathic lithic sandstone and lithic feldspathic sandstone The average porosity is from 7.78% to 9.13% with the average permeability of (0.20 ~ 0.34) × 10-3μm2. Focusing on the relationship between clay minerals and reservoir physical properties, kaolinite and chlorite are the main clay minerals in Chang 6 reservoir, which have a more complicated impact on reservoir physical properties. Small amounts of kaolinite and chlorite tend to predict better reservoir porosity, whereas excess kaolinite (> 7% absolute) and chlorite (> 10% absolute) significantly reduce reservoir porosity degree. By calculation, the initial porosity of Chang 6 reservoir is 41.13% ~ 42.04%, the porosity of sandstone is reduced by 4.52% ~ 4.78% with kaolinite filling, and the loss rate is 10.74% ~ 11.38% The porosity is second only to kaolinite, resulting in a decrease of porosity from 4.12% to 4.70% with a loss rate of 9.81% to 11.18%. Authigenic kaolinite has a certain constructive effect on sandstone permeability, while chlorite results in a decrease of sandstone permeability. The content of illite in the Chang 6 reservoir is lower than that of kaolinite and chlorite, but due to its bridging-type pore filled mainly by silk thread, the porosity and permeability decrease, and the porosity decreases 1.33% ~ 2.08%, loss rate of 3.17% ~ 4.94%. Therefore, the degree of influence of clay minerals on the porosity in the 6th member of tight reservoirs in Jiyuan area is: kaolinite> chlorite> illite.