Tight sandstone gas as one kind of unconventional resources has taken up a significant part in natural gas resource growth in recent years. Tight sandstone gas originated from the definition of U.S. Gas Policy Act of 1978, that regulated in-situ gas permeability to be equal to or less than 0.1 md for the reservoir to qualify as a tight gas formation Gas flow in tight sandstone behaves as non-Darcy flow has been reached a consensus by scholars; however gas-water flow characterization and the main factors for gas-water flow in tight sandstone remain complicated. Scholars proposed that there is a " Permeability Jail" for water-gas flowing in tight sandstone reservoirs which means both water and gas cannot flow in " Permeability Jail" range. This may explain why neither gas nor water produced in tight sandstone reservoir in wells of some tight gas field.
In order to get a better understanding on water-gas flow characteristics and to figure out the major affecting factors for gas-water migration in tight sandstone, we analyses pore structure, bulk and clay mineral constitutes and gas-water two phases flow characteristics of five tight sandstone samples with low permeability (<0.1md) and low porosity from the tight gas fields in Kuqa Depression, Tarim Basin by using of micro CT scanning, XRD analysis and physical simulation experiments.
Experimental results indicate that
" Permeability Jail" does not existed in five tight sandstone samples, but flow ranges for gas-water of five samples are different;
pore structures and fractures play significant roles for the gas-water flowing, and fractures can improve the gas-water permeability significantly;
for permeability, the pore connectivity is more important than total porosity of rocks;
content of clay minerals in tight sandstones affected the gas-water migration, the higher the clay minerals contents are, the lower the permeability of rocks is.