Journal of Conference Abstracts

Compaction-driven Fluid Flow Through a Viscoelastic Matrix: Fluid Flow in the Limit of Zero Initial Porosity

Yura Podladchikov (yura@erdw.ethz.ch)¹ & James Connolly (jamie@erdw.ethz.ch)²

¹Geology-ETHZ, Zurich, 8092, Switzerland

²IMP-ETHZ, Zurich, 8092, Switzerland

Conventional modeling of compaction-driven fluid flow in a viscous matrix assumes uniform connected background porosity. In the context of melt transport, even if the difficulty of maintaining a pervasive melt-filled porosity at subsolidus temperatures is disregarded, the models show that steady flow is unstable. Therefore, it is difficult to envisage a process that could create the initial conditions for the models and be simultaneously consistent with conclusions drawn from the modeling. For this reason, among others, it is essential to investigate propagation of compaction driven fluid flow into a matrix with no initial hydraulic connectivity. There is no solution to this problem for a viscous matrix, but there is no singularity at zero porosity for the propagation of a shock of fluid-filled porosity through an elastic matrix. The physical basis for this propagation is that the infinite fluid pressure gradient across the shock front drives fluid flow into the zero porosity matrix by exploiting microscopic flaws. The shock propagation is limited by the rate of fluid supply to the shock front by viscous compaction at greater depth. To characterize this process we have explored the possible stationary solutions to the viscoelastic compaction equations as a function of matrix (De_(phi)) and fluid (De_f) Deborah numbers. For De_f =0 and De_(phi) >0, we obtain a stationary shock wave solution consisting of a shock front that resembles the pure elastic solution, followed by a viscous wave-like structure that decays to a tail with finite porosity (v 11, Geodin. Acta, 1998). In natural systems where the fluid, or its connectivity, is thermodynamically unstable we anticipate that this tail would detach periodically resulting in loss of fluid mass. For De_f / De_(phi) >= ~1, the solution becomes a solitary wave in porosity. This solution is the only solitary porosity-wave solution to the compaction equations relevant to geological problems.