四川盆地焦石坝地区龙马溪组页岩层序及页岩气“甜点”地震预测
THE SHALE SEQUENCE OF LONGMAXI FORMATION AND SEISMIC PREDICTION OF SWEET SPOTS OF SHALE GAS IN THE JIAOSHIBA AREA, SICHUAN BASIN
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摘要: 我国页岩气勘探开发在四川盆地焦石坝地区龙马溪组已经取得重大突破, 针对性的页岩气"甜点"地球物理技术亟待研究和探索。沉积相是进行页岩气甜点预测和描述的重要基础和依据。应用层序地层学理论, 建立了页岩层段的三级层序地层格架, 认清了深水陆棚页岩沉积相的展布规律, 目的层五峰组及龙马溪组富碳高硅和高碳高硅泥页岩主要分布在三级层序的海侵体系域。在此基础上, 探索了层序地层格架控制下的页岩气"甜点"的地球物理识别和预测方法。研究认为, 页岩气地球物理识别与预测技术在含气页岩有机碳含量(TOC)、裂缝和脆性等方面具有较大的优势, 能为页岩气水平井分段压裂工程和水平井轨迹设计提供有力的技术支持。Abstract: A breakthrough in shale-gas exploration and development has been reached over the past few years in the Longmaxi Formation of the Sichuan Basin in China. Specific geophysical methods and techniques are thoroughly studied and applied for detecting sweet spots. Sequence stratigraphic study suggests that the shale segment belongs to a deep-water shelf deposits. High quality shale mainly occurs in the transgressive systems tracts (TST) of a sequence. Facies analysis is then made, as a most important mean for sequence stratiigraphic study and prediction of sweet spots. Geophysics is the most efficient tool for identification and prediction of sweet spots under the framework of sequence stratigraphy. In addition, it has advantages in determination of organic carbon content (TOC), cracks, brittleness and stress field, etc. and may provide powerful technical support to the fracturing during the stage of horizontal well drilling.