Estimation of permeability structure in an accretionary wedge by useing numerical simulation.

It is important to study the behavior of the fluid in an accretionary wedge such as Nankai-Trough, because it contributes to the finding field resources such as methane hydrate and to prevent natural disasters such as earthquakes and submarine slides. In this research, we aim to examine the influence of the deformation on the behavior of the pore fluid in the structure. We used two numerical simulations, Distinct-Element Method (DEM) and Lattice Boltzmann Method (LBM), to analyze the deformation/fluid flow interaction in the accretionary wedge. The structural model in this research was constructed by the DEM that also calculates the porosity distribution, then the flow speed of fluid and the permeability was calculated by the LBM. As a first step by using 3D DEM, a layer of particles was deposited in a box bounded by 6 walls, and a side wall was pushed inward to cause shortening deformation of an accretionary prism. Then, we calculate the distribution of the porosity from the positions of the particles. We found that the region of low porosity exists in the hanging walls, whereas that of high porosity extends from the footwalls to the surface. Decreased porosity at the base is an indication for tectonic compaction at the base but not tectonic compaction in the wedge. The permeability distribution was calculated the permeability distribution with LBM. Discuss permeability distribution in relation to internal and basal faults and major structures. The permeability difference between the hanging walls and the foot walls coincides with the porosity distribution that is affected by the tectonic deformation. Finally, we simulated the virtual fluid injection into the prism model from the bottom to estimate the fluid flow structure in the model prism. This injection simulation corresponds to the fluid supply from the base decollement. The result shows that the flow velocity is also affected by the fault and the tectonic compaction that corresponds well with the permeability distribution. This research shows that tectonic compaction and faulting due to accretionary process have significant influence to the porosity and permeability structures of the prism.