Stratigraphic variation of transport properties and overpressure development in the Western Foothills, Taiwan
Stratigraphic variation of transport properties and overpressure development in the Western Foothills, Taiwan
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DOI：
10.1029/2008jb005647
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发表时间：
2008-12
影响因子：
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通讯作者：
W. Tanikawa;T. Shimamoto;S. K. Wey;C. Lin;W. Lai
中科院分区：
文献类型：
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作者：
W. Tanikawa;T. Shimamoto;S. K. Wey;C. Lin;W. Lai
台湾西麓中北部中新世中地层以下发育超压，流体压力高于静水压力。为了研究台湾油田超压的产生和维持机制，采用一维盆地模型，结合实验室近似水力参数，估计了台湾油田流体压力历史和超压分布。在5 ~ 200 MPa有效压力下，测量了露头沉积岩的输运特性。各参数均表现出明显的地层差异，随埋深的增加而减小。渗透率对深度的敏感性最强，在盆地底部下降6个数量级至10 ~ 20 m2。地质柱中未发现关键密封层。该盆地模型考虑了沉积物堆积、水的温水膨胀、可膨胀粘土与不可膨胀粘土的脱水反应以及生油等对上覆岩层的影响。预测超压发生在3 Ma以后，由于构造碰撞，聚集速度迅速增加。如果假设流体从盆地底部流入，预测的超压与观测到的超压是一致的，这意味着可能沿滑脱或正断层的深度持续流入可能是本区超压形成的主要原因。地层输运性质的变化随深度而减小，也影响了西麓地区的超压趋势，那里的超压只在较深的层位产生。利用蒙脱石-伊利石动力学脱水模型估算的黏土矿物分布与实测矿物学资料吻合较好。
[1] Overpressure, fluid pressure higher than hydrostatic pressure, has developed below the middle Miocene formations in the north central Western Foothills of Taiwan. To study the mechanism by which overpressure is generated and maintained in the Taiwan oil fields, we estimated the fluid pressure history and overpressure distribution by using a one-dimensional basin model incorporating laboratory-approximated hydraulic parameters. Transport properties of outcropping sedimentary rocks were measured at effective pressures of 5 to 200 MPa. All parameters showed apparent stratigraphic variation, decreasing with increasing burial depth. Permeability showed the strongest sensitivity to depth, decreasing by 6 orders of magnitude to 10−20 m2 at the bottom of the basin. A critical sealing layer was not identified in the geologic column. The basin model incorporates overburden loading due to sediment accumulation, aquathermal expansion of water, the dehydration reaction of expandable clay to nonexpandable clay, and oil generation. Predicted overpressure was generated dramatically from 3 Ma, when the accumulation rate increased rapidly as a result of tectonic collisions in the area. If we assume a fluid influx from the bottom of the basin, the predicted overpressure is consistent with the observed overpressure, implying that continuous inflow from depth, possibly along the decollement or normal faults, may be the main cause of overpressure generation in this area. Stratigraphic variation of transport properties, which decrease with depth, also influences overpressure trends in the Western Foothills, where overpressure is generated only in deeper horizons. The clay mineral distribution estimated by a kinetic smectite-illite dehydration model is consistent with the observed mineralogical data.