鄂尔多斯盆地东南部页岩核磁共振实验研究

Experimental study on the nuclear magnetic resonance of shale in the southeastern Ordos Basin

鄂尔多斯盆地东南部地区页岩气资源开发前景广阔,准确评价不同层位的页岩储层特征意义重大,借助核磁共振实验研究长7段、山西组和本溪组页岩特征,分析页岩孔径分布规律,实验研究表明:(1)页岩T_2谱响应特征表现出Ⅰ类单峰、Ⅱ类双峰和Ⅲ类三峰等3种类型,Ⅱ类双峰态T_2谱在鄂尔多斯东南部页岩中最为发育;(2) T_2截止值分布在0. 49～6. 64 ms,平均1. 57 ms,山西组和本溪组T_2截止值可借助左峰峰值快速确定;(3)核磁孔隙度分布范围为0. 55%～10. 26%,核磁可动流体百分数分布范围为27. 29%～66. 31%,渗透率与孔隙度之间整体呈现幂函数递增关系;(4)长7段页岩裂缝占比3. 49%～10. 13%,山西组页岩裂缝占比4. 89%～27. 52%,本溪组页岩裂缝占比2. 97%～8. 18%,长7段页岩主要发育微细孔隙且孔径分布范围最广,山西组页岩裂缝发育程度最高,本溪组部分页岩存在少量大尺寸裂缝;(5)鄂尔多斯东南部地区山西组和本溪组页岩开发效果优于长7段页岩,推荐山西组和本溪组作为页岩气开发的主力层位。

The shale gas resource in the southeastern region of Ordos Basin has a broad development prospect,and it is of significance to accurately evaluate the different characteristics of multiple layers in shale gas reservoirs.By means of nuclear magnetic resonance(NMR)experiments,the characteristics of the shale in Chang 7,Shanxi and Benxi Formations are studied,and the pore distributions of these three shales are analyzed.The experimental results show that①the T2 spectral response of shale presents three types,single peak,two peaks,and three peaks.In this study,the T2 spectrum with two peaks are most developed in shales;②the T2 cut-off values range 0.49-6.64 ms with the average value of 1.57 ms,and the T2 cut-off values for Shanxi shale and Benxi shale can be quickly determined by the peak of the left spectral front;③the distribution of NMR porosity ranges 0.55%-10.26%,the distribution of NMR mobile fluid percentage ranges 27.29%-66.31%,and the permeability increases with porosity in a power law function;④the fracture system of Chang 7 shale accounts for 3.49%-10.13%,the fracture proportion for Shanxi shale is 4.89%-27.52%,the fracture proportion for Benxi shale is 2.97%-8.18%,the pores mostly develop in Chang 7 shale,the fractures most richly develop in Shanxi shale,and there are a few large size fractures in some Benxi shales;⑤the development effects of Shanxi formation and Benxi Formation are better than that of Chang 7 formation,and Shanxi Formation and Benxi Formation are recommended as the main development layers for shale gas reservoirs in the southeastern Ordos region.