基于岩石物理分析的页岩气叠前预测方法在川南威远地区的应用

在页岩气勘探开发中,地球物理技术发挥着不可替代的重要作用。为了探索地震参数与页岩气储层评价参数之间的关系,对四川盆地长宁—威远地区五峰组—龙马溪组岩石物理实验的分析结果表明,岩心总有机碳(TOC)含量和岩心总含气量与纵横波速度比的相关性相对最好。当纵横波速度比逐渐增大时,岩心TOC含量和岩心总含气量整体呈逐渐减小的趋势,这一结果可以指导页岩气储层TOC含量和总含气量的预测。结合测井评价对多种岩石物理参数开展页岩气储层的敏感性分析认为,纵横波速度比是识别页岩气储层最有效的参数。基于岩石物理分析结果建立页岩气储层TOC含量、总含气量与纵横波速度比之间的对应关系,并利用叠前反演技术和岩石力学脆性评价方法对四川盆地南部威远地区W4井区五峰组—龙马溪组页岩气储层厚度、TOC含量、总含气量和脆性指数等评价参数进行定量预测,根据预测结果对研究区页岩气储层开展综合评价,可为确定页岩气核心建产区及其开发方案提供有力技术支撑。

Application of pre-stack prediction method of shale gas based on petrophysical analysis in Weiyuan area of the southern Sichuan Basin

In shale gas exploration and development, geophysical technology is of indispensable significance. To explore the relationship between the seismic parameters and the evaluation parameters of shale gas reservoirs, the analysis results of petrophysical experiments conducted on Wufeng Formation-Longmaxi Formation in the Changning-Weiyuan area of Sichuan Basin show that the correlations between the total organic carbon (TOC)contents of cores, the total gas contents of core and the P- to S- wave velocity ratios are relatively best. When the P- to S-wave velocity ratio gradually increases, the TOC contents and the total gas contents of cores gradually decrease. This result can guide the prediction of TOC contents and total gas contents of shale gas reservoirs. The sensitivity analysis of shale gas reservoirs on a variety of petrophysical parameters combined with logging evaluation suggests that the P- to S-wave velocity ratio is the most effective parameter for identifying shale gas reservoirs. Based on the petrophysical analyses, this paper establishes the corresponding relationship between the TOC contents, the total gas contents and the P- to S-wave velocity ratios of shale gas reservoirs, and by using the pre-stack inversion technique and the evaluation method of rock brittleness, quantitatively predicts the evaluation parameters such as shale gas reservoir thickness, TOC content, total gas content, and brittleness index of the Wufeng Formation-Longmaxi Formation of Well W4 in Weiyuan area in the southern Sichuan Basin. According to the prediction results, a comprehensive evaluation of shale gas reservoirs in the study area is performed, which can provide powerful technical support for determining the core production area of shale gas and its development program.