Improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that intersects a horizontal cavity well. The drainage patterns provide access to a large subterranean area from the surface while the vertical cavity well allows entrained water, hydrocarbons, and other deposits to be efficiently removed and/or produced.

To be accompanied, when published, by Figure 1 of the drawings.

Improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that intersects a horizontal cavity well. The drainage patterns provide access to a large subterranean area from the surface while the vertical cavity well allows entrained water, hydrocarbons, and other deposits to be efficiently removed and/or produced.

To be accompanied, when published, by Figure 1 of the drawings.

Gas permeability of very low permeability subterranean formations, and the gas permeability reducing effects of injecting one or more treatment fluids thereinto, are measured by injecting a gas into a core sample of the formation at a selected substantially constant pressure, and continuing the injection for a long period of time to ensure steady state flow conditions. The temperature of the gas as it flows through the core sample and the flow rate of the gas exiting the core sample are measured, and the native state gas permeability of the core sample is calculated therefrom. One or more treatment fluids can be injected into the core sample after the native state permeability is determined. Thereafter, the gas permeability can again be determined and compared to the native state permeability.

A fuel gas, typically methane, is produced from a coal seam penetrated by an injection well and a gas production well by first introducing liquefied or gaseous carbon dioxide through the injection well into the coal seam and subsequently introducing a weakly adsorbable gas, for example nitrogen, through the injection well and into the coal seam. As the weakly adsorbable gas passes through the coal seam, it forces the carbon dioxide through the seam. If the carbon dioxide is in liquefied form, it evaporates as it moves through the seam, and the carbon dioxide gas desorbs methane from the coal and sweeps it toward the production well. The methane is withdrawn from the seam through the production well.

A method for the underground gasification of coal or browncoal, using two boreholes (1, 2) extending through a coal layer (3) with the slope of said layer, for supplying oxygen to a combustion and gasification front in said layer and discharging combustion gases respectively, a filler material being intermittently supplied through one of said boreholes for filling the cavity produced by burning away the coal layer. According to the invention, said filling is started at a moment before the combustion front has reached the discharge borehole, and in particular before the overlying formations will collapse to such a degree that an inadmissible subsidence at the ground level would develop. Thereafter the combustion and gasification is restarted in the same or the opposite sense as may be required for adjusting the orientation of the gasification front in the desired direction.