The Tiehchanshan structure of NW Taiwan: A potential geological reservoir for CO2 sequestration

  • Author(s): Kenn-Ming Yang, Bo-Iuan Chuang, Ching-Yun Hsieh, Bee-Der Yuan, Hsin-Hsiu Ting, and Jar-Ben Wang
  • DOI: 10.3319/TAO.2017.05.25.01
  • Keywords: Carbon dioxide sequestration, Structural geology, Sequence stratigraphy, Tiehchanshan structure
  • Softly linked subsurface settings with opposed vergence of Tiehchanshan structure
  • Kinematics and strain variation of thrust-related folds
  • Stacking pattern of sequence units of sandstone layers for CO2 storage
Abstract

In the outer foothills belt of northwestern Taiwan, the Tiehchanshan structure is a complex anticline among a train of fault-related folds that are segmented and geometrically affected by a set of pre-existing transcurrent faults. The structure is the largest gas-field in western Taiwan and has been regarded as the best site for CO2 sequestration. In spite of its simple surface geometry, its subsurface structure remains debatable. This study used a grid of seismic sections and wellbore data to establish a new 3-D geometry of subsurface structure, which was combined lithofacies characters of the target reservoir rock, the Yutengping Sandstone, to build a geological model for CO2 sequestration.On the surface, the Tiehchanshan structure is characterized by two segmented anticlines offset by a tear fault striking at high angle to the fold axis. The subsurface geometry of the Tiehchanshan structure is, however, composed of two anticlines with opposite vergence divided by a transfer, implying that the separated folds are related to slip along the thrusts with opposite dip direction. The subsurface transfer structure can be manifested by increasing fold symmetry and decreasing dip angle and slip of fold-forming thrust toward the surface and by local change in strike of fold axis. The mapped axial surface strongly suggests that the folds of opposite vergence are softly linked in the subsurface, implying that the suspected tear fault in the surface transfer zone may not exist in the subsurface. The subsurface transfer zone, located in the area to the south, is much wider than the surface transfer zone.The Yutengping Sandstone is composed of several sandstone units characterized by coarsening-upward cycles, with few interbedded fining-upward cycles. The sandstone member can be further divided into four well-defined sandstone layers, which are separated by laterally continuous shale layers. In view of the structural and stratigraphic characteristics, the optimum area for CO2 injection and storage is in the structurally highest part of the Tunghsiao anticline in the northern part of the Tiehchanshan structure. The integrity of the closure and the overlying seal are not disrupted by the pre-orogenic high-angle faults. On the other hand, a thick continuous shale layer within the Yutengping Sandstone isolates the topmost sandy layer from the underlying ones and gives another important factor to the CO2 injection simulation.

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