Secondary gas migration limited by fractured rock.

摘要

We present a conceptual and quantitative model to describe the interactions between minimum horizontal stress, pore pressure, and fracture permeability. The model is then coupled with a one-dimensional vertical fracture flow model to investigate the gas column height which can be trapped by a fractured caprock during steady-state gas migration. One and two-dimensional transient numerical flow models are developed to evaluate the formation of a gas cap within reservoir sands underlying fractured caprock. The model assumes that all flow in the caprock is via fracture permeability and that this permeability is a function of the effective minimum horizontal stress in the caprock. The absolute stress state within the caprock is assumed to be uncoupled from the pore pressure. Trap integrity is shown to depend strongly on the water charge rate, the fracture permeability model and the rock properties.