多方法协同表征特低渗砂岩储层全孔径孔隙结构——以鄂尔多斯盆地合水地区砂岩储层为例

Multi-method synergistic characterization of total pore structure of extra-low permeability sandstone reservoirs: case study of the Heshui area of Ordos Basin

欧阳思琪 孙卫 黄何鑫

OUYANG Siqi SUN Wei HUANG Hexing

西北大学 地质学系, 西安 710069

Department of Geology, Northwest University, Xi'an, Shaanxi 710069, China

高压压汞、恒速压汞、核磁共振实验在表征特低渗透砂岩储层的微观孔隙结构时存在局限性，其结果与铸体薄片和扫描电镜观察到的特征吻合度不高。为了解决这一问题，更加精细地刻画孔喉分布特征，以鄂尔多斯盆地合水地区砂岩储层样品为例，提出了多方法协同表征全孔径孔喉结构的方法。利用高压压汞所得毛管压力曲线与核磁共振联合高压压汞计算所得的伪毛管压力曲线对比，根据喉道分类分别计算吸附喉、微喉、细微喉、中细喉对应的孔隙空间的连通比。根据核磁共振实验原理，利用公式实现横向弛豫时间向孔径的转换，公式中比表面积利用高压压汞计算，弛豫率利用恒速压汞对比核磁共振T2谱标定，将协同计算所得孔喉分布结果与对应的孔喉连通比相乘得到不同尺度喉道及孔隙连通空间分布曲线。结果显示：吸附喉连通比最低，其他类型的喉道连通比较高，且差异不大。喉道分布范围（0.003~3.661 μm）较恒速压汞结果变大，孔隙半径（0.8~91.4 μm）减小，孔喉比（16.4~58.6）减小，与铸体薄片与扫描电镜观察结果基本相符。说明多种方法协同计算一定程度上克服了高压压汞喉道与孔隙的叠加以及恒速压汞的计算误差，更接近于储层真实状态。

Mercury injection capillary pressure (MICP), rate-controlled porosimetry (RCP) and nuclear magnetic resonance (NMR) have limitations in describing the characteristics of microscopic pore structure characteristics of extra-low permeability sandstone reservoirs, and the results are not completely consistent with the observation of thin sections and scanning electron microscopy. Five ultra-low permeability sandstone reservoir samples were collected from the Heshui area of Ordos Basin. A collaborative multi-method for characterizing pore throat structure was proposed in order to describe the detailed characteristics of pore size distribution. MICP and NMR combined with MICP were used to obtain pore connectivity. The connectivity ratio of adsorption throat, micro throat, fine throat, middle throat was calculated. Nuclear magnetic resonance data were used to achieve the conversion of transverse relaxation time to pore throat radius. The specific surface area was calculated by MICP, and the relaxation rate was calibrated by RCP and the T2 spectrum. The synergistic calculated pore throat distribution results were multiplied by the corresponding pore throat connectivity ratio to obtain the spatial distribution curves of throat and pore connectivity at different scales. The results showed that the adsorption throat connectivity ratio was the lowest, and the ratio of other sizes was relatively higher, but the difference is not significant. The throat radius ranged from 0.003 to 3.661 μm, which was greater than constant rate-controlled porosimetry test results. The pore radius ranged from 0.8 to 91.4 μm and the pore-throat ratio ranged from 16.4 to 58.6 μm, both of which were smaller than rate-controlled porosimetry test results. The final calculation results were basically in accordance with the observed results of cast thin section and scanning electron microscopy. It showed that the collaborative calculation of multiple methods overcomes the superposition of throat and pores on high-pressure mercury-injection and the calculation error of rate-controlled porosimetry, which is closer to the true state of reservoir.

国家科技重大专项“大型油气田及煤层气开发”（2011ZX05044）和国家自然科学基金（41702146）资助。

https://doi.org/10.11781/sysydz201804595