非常规油气储层脆性指数测井评价方法研究进展

Research progress in brittleness index evaluation methods with logging data in unconventional oil and gas reservoirs

非常规油气储层一般都需要进行压裂改造才能获得工业产能,而岩石脆性指数测井评价是非常规油气储层压裂设计中应考虑的重要因素之一。目前国内外关于脆性指数定义众多、且计算方法各异,在关于脆性指数的测井评价方法方面更是缺少一套完整的研究方法流程。本文回顾了油气储层脆性指数的研究历程,明确了脆性指数定义的科学内涵,归纳总结了脆性指数的测井评价方法。最后以鄂尔多斯盆地长7致密油储层为例,探讨了主要的脆性指数测井评价方法计算流程及其有效性。在有纵、横波测井资料时,可利用泊-杨法直接计算岩石脆性指数。同时也可通过元素俘获测井矿物成分比值法计算脆性指数。此外基于常规测井的最优化方法确定矿物组分,利用矿物成分比值法也能计算脆性指数。通过X-射线衍射资料与岩性系数GR/Pe的回归拟合建立地区经验公式,也可实现岩石脆性指数的测井评价。最后对脆性指数测井计算中存在的问题进行归纳总结,并对未来发展方向做出展望。研究成果可为非常规油气储层钻井和压裂设计工作提供科学指导。

Unconventional oil and gas reservoirs typically require fracturing to achieve industrial capacity. Logging evaluation for rock brittleness is one of the important factors that should be considered in the design of fracturing for unconventional oil and gas reservoirs. At home and abroad,the brittleness index is defined variably and calculated by different methods. However,there is a lack of a complete research method flow for brittleness index evaluation with logging data. This paper reviews the history of the oil and gas reservoir brittleness index,provides a scientific evaluation of brittleness index definitions and summarizes brittleness index calculation methods. Finally,the Chang 7 tight oil reservoir in Ordos Basin is taken as an example for discussing the calculation processes and effectiveness of logging evaluation methods for brittleness index. When there are comprehensive wave and shear wave logging data,the rock brittleness index can be calculated directly by Poisson's ratio and Young's modulus method or by using mineral composition which could be gained from either Elemental Capture Spectroscopy(ECS)logging curves or optimization method based on conventional logging data. X-ray diffraction data and regression of GR/Pe can also be used to establish an empirical formula for the brittleness index which is suitable for the target study layers to achieve logging evaluation of the brittleness index. Finally,the problems existing in the brittleness index evaluation with logging data are discussed,and the future development direction is put forward. The research results can provide scientific guidance for drilling and fracturing layer optimization of unconventional oil and gas reservoirs.