基于测井数据的页岩可压性定量评价

Quantitative evaluation of shale fracability based on logging data

可压性是指在压裂过程中页岩发生有效破裂的能力。目前对可压性的研究主要基于定性评价,或建立在岩石力学实验和压裂施工参数基础上的定量评价,难以完整连续地表征非均质性较强的页岩在水平井长水平段的可压性变化。基于测井数据,评价了页岩脆性指数、脆性矿物质量分数、断裂韧性、黏土矿物质量分数和总有机碳质量分数对可压性的影响,并利用层次分析法和模糊数学法,从定性和定量相结合的角度建立了页岩长水平段的连续可压性数学模型,且划分了可压性级别。该模型将可压性划分为3个级别:当可压性指数高于0.48时,页岩的可压性好;当可压性为0.32~0.48时,页岩的可压性中等;当可压性低于0.32时,页岩的可压性较差。研究表明,利用测井数据能够更全面细致地评价沿水平井长水平段的页岩可压性,对压裂设计和射孔参数设计具有更好的指导性。现场应用表明,该模型能够较准确连续地预测页岩可压性,且具有广泛的适用性。

Fracability is the capability of the shale that can be fractured effectively during fracturing process. At present, the research on the fracability is mainly through the qualitative evaluation and quantitative evaluation based on the rock mechanics test and fracturing construction parameters, which is difficult to fully characterize the variability of the shale fracability that has strong heterogeneity in horizontal wells. Based on the logging data, and by analyzing the influence of shale brittleness index, brittle mineral content, fracture toughness, clay mineral content and TOC content on the fracability and taking advantage of the analytic hierarchy process and fuzzy mathematics method, a fracability mathematical model of the long horizontal section of the shale is established by the combination of the qualitative and quantitative analysis and the level of shale fracability is divided. It is also indicated that fracability is divided into 3 levels according to this model, that is when the fracability index is higher than 0.48, shale fracability is good; when the fracability index is between 0.32 and 0.48, shale fracability is medium; when the fracability index is lower than 0.32, shale fracability is poor. The results show that the logging data can be more comprehensive and detailed to evaluate the fracability of the long horizontal interval of the shale, which provides a good guide for the design of fracturing and perforation parameter. Field application shows that the model can accurately predict the shale fracability and has a wide range of applicability. So this model can be used in the fracability evaluation of shale gas blocks.