This paper examines a mechanistic approach to study fluid flow in shale plays both in small-scale and field-scale. Kerogenic material in shales is the source of hydrocarbon molecules. Hydrocarbon molecules in shale can be stored as compressed gas in pore network, as desorbed gas on the inner surface of meso and micro pores inside kerogen, and as dissolved gas in the body of the kerogen. At the early stage of production, gas decompression within pore network is the dominant mechanism; however, diffusive flux from the bulk of kerogen will be triggered later to substitute the desorbed molecules. Detailed studies of scanning electron microscope images reveal the large exposed surface area in kerogenic material. This new finding suggests that although the gas diffusion coefficient is very low in kerogen, the diffusive flux could be considerable because of the large exposed area.

We develop a simulation tool to model fluid flow in lab-scale. In our simulations, the flow are classified into three different regimes:

  1. diffusive flow through macropores;

  2. molecular desorption from the pore surface in kerogen and the subsequent flow through meso pores under slip condition; and

  3. diffusive flux from kerogen bulk to the pore surface, which is very slow process. A sensitivity study is carried out to investigate impact of desorption properties and diffusion coefficients on flow rates and the production recovery.

In this study, we present a conceptual dual-fracture triple-porosity model to evaluate interconnectivity of fractures and their contribution to the production performance. The new model especially is helpful in field-scale studies as the production performance is governed through the extension of the fracture rather than their individual aperture or size.

The main contribution of this work is development of a framework to estimate stimulated reservoir length and the effective diffusion coefficients for both gas and oil phases using field production data. Prediction of gas/liquid flux would significantly impact economic evaluations of shale reservoirs.

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