Abstract
In one of the largest oil-gas fields in Daqing, China, the anticlines are important structures that hold natural gas. The origin of the symmetric anticlines, which have bends on both the limbs, remains under debate. This is especially true in the case of the anticline in Xujiaweizi (XJWZ), which has recently been the focus of gas exploration. A compressive force introduced by a ramp/flat fault was suggested as its origin of formation; however, this is inconsistent with the reconstruction of the regional stress fields, which show an extensive environment. An alternative explanation suggests a normal fault-related fold under extensive stress. However, this mechanism has difficulty explaining the very localized, rather than wide-spread, development of the anticline along the proposed controlling normal fault. The well-developed bends on both limbs of the anticline are also very different from the typical roll-over anticline. Here, we conduct an experimental study showing that the very localized development of the bent-on-both-limbs anticline is controlled by the geometry of the underlying fault-plane. A ramp/flat fault plane can introduce an anticline with bends on both limbs, while a smooth fault plane will develop a roll-over anticline with a bend on only one limb.
Highlights
The anticline in Xujiaweizi (XJWZ) is the focus of recent natural gas exploration in Daqing (Fig. 1)[1], one of the largest oil-gas fields in China[2]
The anticline only formed in the middle of the XJWZ depression, and no anticline with a well-developed geometry can be observed in the adjacent region along the proposed controlling fault (Fig. 2b)
The dynamic processes that correspond to the formation of the symmetric anticline on the ramp/flat fault plane have been observed in the 2-D simulation (Fig. 3)
Summary
The anticline in Xujiaweizi (XJWZ) is the focus of recent natural gas exploration in Daqing (Fig. 1)[1], one of the largest oil-gas fields in China[2]. The anticline only formed in the middle of the XJWZ depression, and no anticline with a well-developed geometry can be observed in the adjacent region along the proposed controlling fault (Fig. 2b). It has been noted that the geometry of the normal fault-related folds is associated with the shape of the underlying fault plane[8, 9]. The geometry of the underlying fault plane may have controlled the formation of the XJWZ anticline. A 3-D simulation with a boundary condition that is similar to the XJWZ depression was conducted to examine the response of the fold geometry to the underlying plane shape. Fault-depression inversion stage Strong rifting stage Initial rifting stage simulated results show consistency with the observed structure in the XJWZ depression, which provides rather robust evidence for the control of the underlying fault shape on the formation of the XJWZ anticline
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