Co-production of Tight Gas and Coalbed Methane from Single Wellbore: a Simulation Study from Northeastern Ordos Basin, China

Focusing on vertical multi-layer superimposition of unconventional natural gas reservoirs in coal-bearing strata, research on the co-production of tight gas and coalbed methane from a single wellbore was conducted. This study intended to obtain maximum economic benefit of a single well from multi-layers. According to the vertical combination of tight sandstone and coal in the eastern Ordos Basin, the reservoir combinations were classified into direct contact, fracture connected, and non-contact types. Based on the economic benefit of co-production, the inter-layer interference coefficient and applicability coefficient were established. The productivity of tight gas and coalbed methane co-production from one wellbore was numerically simulated using the black oil model. The results indicated that with increase in reservoir permeability, thickness, and average pressure, as well as the decrease in reservoir differential pressure, the combined gas production increased. Gas production rate from different reservoir combination types can be ranked in the following order: direct contact type > fracture connected type > non-contact type. In addition, with increase in permeability ratio (sandstone permeability vs. coal permeability) and average pressure, as well as with decrease in differential thickness and differential pressure, the co-production applicability increased. In addition, for different reservoir combinations, non-contact type co-production can be the first choice, and the next choice is fracture connected type. The results can be beneficial for conducting co-production choice in different unconventional natural gases superimposed basins.