Shales in the Qiongzhusi and Wufeng-Longmaxi Formations: a rock-physics model and analysis of the effective pore aspect ratio
Shales in the Qiongzhusi and Wufeng-Longmaxi Formations: a rock-physics model and analysis of the effective pore aspect ratio
复制标题
筇竹寺组、五峰组—龙马溪组页岩：岩石物理模型及有效孔隙纵横比分析
DOI：
10.1007/s11770-017-0628-7
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发表时间：
2017
影响因子：
0.7
通讯作者：
Zou Chang-Chun
中科院分区：
文献类型：
--
作者：
Yang Zhi-Qiang;He Tao;Zou Chang-Chun
四川盆地及周边地区的琼珠寺组和五峰组-龙马溪组页岩是目前我国页岩气勘探开发的重要层位。然而，地震弹性特性的区域特征需要更好地确定。在干燥条件下测量了泥页岩样品的超声波速度，系统分析了泥页岩弹性性质与岩石学的关系。结果表明：1）有效孔隙度与粘土含量呈正相关，与脆性矿物呈负相关; 2）干页岩基质由粘土、石英、长石和碳酸盐组成; 3）有机质和黄铁矿存在于孔隙空间中，与页岩基质弱耦合。因此，通过假设所有连通的孔隙只存在于粘土矿物中，并使用Gassmann替代方法来计算孔隙中有机质和黄铁矿的弹性效应，结合自洽近似（SCA），微分有效介质（DEM）和Gassmann方程，一个相对简单的岩石物理模型被构建。此外，有效孔隙纵横比采用从样品平均值或估计从碳酸盐含量。所提出的模型被用来预测P波速度和一般匹配的超声波测量非常好。
The shales of the Qiongzhusi Formation and Wufeng–Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1) the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2) the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3) organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation (SCA), the differential effective medium (DEM), and Gassmann’s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well.