富有机质页岩TOC含量的地球物理定量化预测

四川盆地涪陵地区页岩气已经实现了工业化开采,而TOC含量是评价页岩有机质丰度和生烃能力的主要参数之一。利用测井资料评价烃源岩TOC含量, 能够弥补烃源岩取心少、实测样品分布不连续的不足。为了得到连续的、整体的TOC含量数据,达到对页岩含气层位有机碳含量的定量化预测的目的,以涪陵地区A井为例,从目的层五峰-龙马溪组页岩实测TOC含量出发,结合地球物理测井资料,采用多参数优选、交会分析法、多元回归分析及ΔlgR法寻找与TOC相关性最好的参数,并以此建立区域性的统计学方程。利用该拟合关系式,结合三维地震数据体的叠后反演,计算出TOC数据体。结果显示,预测TOC结果与实测值高度吻合,相关性好,误差小。计算得到页岩目的层位TOC含量为0.5%～5.15%。其中目的层第一段TOC含量为1.9%～5.15%,为优势层段。地震反演得到的TOC连井分布和平面分布特征与研究区4口井的实测与计算TOC值连井对比所表现的分布特征一致。表明用岩石测井密度与TOC关系所预测的TOC分布是准确可信的,此方法可以应用于涪陵地区页岩的勘探评价。

TOC content quantitative prediction in organic-rich shale

Industrial development of shale gas has been achieved in the Fuling area, Sichuan Basin. Total organic carbon (TOC) content is one of the most critical indexes for organic matter abundance evaluation and hydrocarbon generation potential in shale. TOC content evaluation in source rocks from well logging can make up for the insufficiency of rock cores. We propose in this article an approach of TOC content quantitative prediction. Based on measured TOC content and well logging data from Wufeng-Longmaxi formation in the Well A, Fuling, the most sensitive parameter to TOC is found out with multi-parameter optimization, cross-plot analysis, multiple regression analysis, and ΔlgR method. Then an optimal fitting statistical equation between the sensitive parameter and TOC is established, and an empirical formula is obtained for TOC calculation. Finally a TOC volume is calculated with the optimal fitting statistical equation and 3D seismic poststack inversion to realize TOC content quantitative prediction. The results reveal that the predicted TOC values highly coincide with the measured values.Calculated TOC content values of the target members are between 0.5%~5.15% and the first member is 1.9%~5.15%. The TOC planar distribution characteristics obtained by 3D seismic inversion are consistent with the measured and calculated TOC data from 4 wells in the area. Our application shows that the proposed TOC prediction approach is accurate and reliable, and could be used for shale gas exploration and evaluation in the area.