基于岩石物理实验的页岩脆性测井评价方法

Petrophysical experiment-based logging evaluation method of shale brittleness

页岩的脆性特性对其储层压裂改造效果有着重要的影响,岩石物理实验与测井技术相结合既能够获得直接的脆性参数,又能保证所取资料的连续性。为此,针对四川盆地蜀南地区下志留统龙马溪组页岩岩样开展了综合研究,形成了一套系统的、基于岩石物理实验的脆性指数测井评价方法:首先,通过岩石物理实验,建立页岩动静态参数的转换模型,可将测井计算的动态参数较好地转换为静态参数,大大提高了测井计算页岩脆性指数的精度;其次,针对页岩岩样进行矿物成分测定,进一步分析确定了影响该区页岩压裂改造的主要脆性矿物,取得了实验与理论的突破。结论表明:1当黏土含量大于40%时,岩石脆性明显降低,当黏土含量小于40%时,岩石脆性指数与黏土含量关系不明显;随着石英+长石+白云石含量的增加,岩石脆性增大,随着方解石含量增高,岩石脆性略有降低。2当测井资料齐全,有纵横波和密度测井资料时,所建立的页岩脆性指数计算方法(即泊—杨法和矿物含量法)计算的页岩脆性指数结果精度较高;当测井资料较少,无阵列声波测井时,矿物成分法作为泊—杨法的补充,同样能够较准确地评价页岩的脆性。该研究成果为现场试油层位优选及储层改造提供了技术支撑。

Shale Brittleness has important influence on the effect of fracturing stimulation.With the integration of petrophysical experiments and logging interpretation,brittleness parameters can directly be obtained and the continuity of the achieved data can be ensured.Based on the comprehensive study of shale samples from the Lower Silurian Longmaxi Fm in the Shunan area of the Sichuan Basin,we developed a set of petrophysical experiment-based systematic logging evaluation methods of shale brittleness.First,a transformation/alternative model between the static and dynamic parameters of shales was built based on petrophysical experiments.It could well transform the dynamic parameters calculated with logging data into static parameters,and thus greatly improved the accuracy of the calculated shale brittleness index.Then,the main brittle minerals that influence fracturing of shales in the study area were identified through the analysis of mineral components,realizing both experimental and theoretical breakthroughs.（1） When the content of clay is larger than 40％,the brittleness of shales significantly lowers; when it is lower than 40％,there is no obvious correlation between clay content and shale brittleness.In addition,shale brittleness enhances along with the increase of quartz,feldspar,dolomite contents,while lowering with the increase of calcite content.（2） When logging data are well integrated with longitudinal wave,compressional wave and density logging data available,the Possion-Young＇s modulus method can accurately calculate shale brittleness; but when logging data are incomplete with no array sonic logging data available,the mineral component method,as a supplement of the Possion-Young＇s modulus method,can also accurately evaluate shale brittleness.The study results provide technical support for the on-site selection of intervals for oil testing and reservoir stimulation.