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四川盆地及其周缘地区的筇竹寺组和五峰-龙马溪组页岩是目前国内页岩气勘探的主要层位之一,但其地震弹性性质响应规律的区域性特征需要开展相关的实验和理论研究工作予以明确。本研究对干燥状态下的筇竹寺组和五峰-龙马溪组页岩的露头样品进行了超声波速度测试,系统地分析了地震弹性性质随页岩岩石学特征的变化规律。研究结果表明,孔隙度与粘土矿物含量呈正相关、与脆性矿物含量呈负相关;粘土、石英、长石和碳酸盐构成页岩岩石基质,与孔隙共同构成页岩岩石骨架,而干酪根和黄铁矿主要赋存于孔隙中,与页岩骨架的耦合较弱。通过将全部连通性孔隙近似等效于仅存在于骨架粘土矿物之内和采用Gassmann流体替换类似的思路处理干酪根和黄铁矿,可以较为简单地将自相容近似(SCA)理论、微分等效介质模型(DEM)和Gassmann方程组合起来构建研究区页岩的地震岩石物理等效模型。该模型通过关键参数等效孔隙纵横比(采用研究区样品平均值或者由碳酸盐含量进行估算)可以较为准确地预测筇竹寺和五峰-龙马溪组页岩的纵波速度,验证了等效模型的有效性和较广的适用性,可为筇竹寺组和五峰-龙马溪组页岩气储层的测井解释和地震“甜点”预测提供依据。
The Qiongzhusi Formation and the Wufeng-Longmaxi Group shale in the Sichuan Basin and its peripheral areas are one of the main strata of shale gas exploration in China at present. However, the regional characteristics of the seismic elastic property response law need to carry out relevant experiments and Theoretical research work to be clear. In this study, the ultrasonic velocity of outcrop samples of Qiongzhusi Formation and Wufeng-Longmaxi Formation in dry state was tested, and the variation regularity of seismic elastic properties with shale petrology characteristics was systematically analyzed. The results show that the porosity is positively correlated with clay mineral content and negatively correlated with brittle mineral content. Clay, quartz, feldspar and carbonate constitute the shale rock matrix, which together with the pores form the shale rock skeleton, while the kerogen and yellow Iron ore mainly occurs in the pores, and its coupling with the shale framework is weak. By approximating all connectivity pores to be present only within framework clay minerals and treating kerogen and pyrite with a similar concept of Gassmann fluid replacement, the self-consistent approximation (SCA) theory, differential, etc., can be relatively simple The effective medium model (DEM) and the Gassmann equation are combined to construct the seismic petrophysical equivalent model of the shale in the study area. The model can predict the P-wave velocities of Qiongzhusi and WFeng-Longmaxi shale more accurately by the equivalent aspect ratio of the key parameters (using the average of the sample in the study area or the carbonate content) The validity of the model and its wide applicability can provide the basis for logging interpretation and earthquake prediction of “Shaoqisi Formation” and “Wufeng-Longmaxi Shale” reservoir.