UNDERSTANDING UNCONVENTIONAL GAS

摘要

In conventional gas production, wells are drilled to target accumulations of free gas that have been trapped over geological time in permeable porous rocks such as sandstones. The gas in these formations has migrated from source rocks (such as organic shales) and become trapped between underlying water and low-permeability 'seal' rocks. These traps have typically resulted from faulting, folding or other stratigraphic and structural features. In contrast, unconventional gas is dispersed within predominantly low-permeability formations such as shale, coal and low-porosity or 'tight' sandstone. In coal seam gas and shale gas plays, the host formation is also usually the source rock, and hence the gas in these targets has not migrated significantly.