Co-production of gas from both coalbeds
and tight formations is
considered a viable means to improve well productivity. Most previous
studies focused on the geology and resource estimates for gas production
viability with little attention to the effectiveness of gas co-production
with regard to well types. To make up for this weakness, a two-phase
flow and reservoir deformation coupled model is proposed together
with an anisotropic permeability model. The coupled model is first
verified using gas and water production data from a vertical well
from the Linxing block in the Ordos Basin, China. Then a reservoir
model is built, including one coal seam and one tight gas formation
separated by a low-permeability stratum with four simulation scenarios
designed. Based on the results, the impacts of the crossflow between
different reservoirs are addressed and the mechanisms of the gas co-production
rate profile types observed in the Linxing block are analyzed. It
is also found that high water-saturated adjacent reservoirs would
keep the water relative permeability of the gas-rich reservoir at
a high level, impeding the gas flow. The use of a horizontal well
is strongly recommended when most gases are stored in a specific thin
reservoir and the life of the well is short; however, a vertical well
is favored when two or more gas-rich and high permeability reservoirs
co-exist and the well life is relatively long. For the application
of vertical wells, the hydraulic fractures should extend in the horizontal
planes and interact with the pre-existing natural fracture. For horizontal
wells, the hydraulic fracture should extend in the host reservoir
and penetrate into the adjacent strata. This work can shed new light
on the co-exploitation of coal measure methane.
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