Effect of distinguishing apparent permeability on flowing gas composition, composition change and composition derivative in tight- and shale-gas reservoir

• MCP means different apparent permeability for the different components.
• MCP is an important factor for wellhead flowing composition (WHFC) variant.
• WHFC is 100% caused by MCP for no adsorption gas reservoirs.
• WHFC reflects adsorption content.
• MCP can improve the accuracy of reservoirs parameter interpretation.

Multi-flow mechanisms co-exist in tight- and shale-gas reservoirs such as slip flow, transition flow, and free molecular flow, thus apparent permeability is used to correct the flow deviation caused by the traditional Darcy’s law. Strictly speaking, apparent permeability is also different for different gas components, which we call as multi-component permeability (MCP). In this paper, we use a compositional model incorporating extended Langmuir isotherm and slippage corrected MCP to study the effect of distinguishing apparent permeability for different components on the curves of wellhead flowing composition (WHFC) and its derivative. A fully implicit iterative numerical solution based on PEBI (Perpendicular Bisection) gridding generates 12 simulations to investigate WHFC, composition change (dc) and composition derivative (dc′) with and without using MCP for a fractured vertical well in the reservoirs with different adsorption capacities. We find that MCP is an important factor for CH4 component variance, especially CH4 component variance is solely caused by MCP for reservoirs without adsorption gas, which shows that MCP can improve interpretation accuracy based on the measured composition. Another finding is that the behavior of WHFC is obviously different between reservoirs with and without adsorbed gas, which can be used to determine whether reservoirs contain adsorption gas or not.

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