Modeling Multicomponent Gas Flow in Liquids Rich Shales

Abstract

Production data acquired from liquids-rich shale reservoirs show a few very interesting trends: 1. A relatively constant gas-oil ratio (GOR) or condensate-gas ratio (CGR) although flowing bottomhole pressures may be below the fluid saturation pressures. 2. Produced fluid compositions are generally different from in-situ fluid compositions even though the GOR/CGR may be constant. These observations are unique to liquids-rich shale wells and are not seen in conventional reservoirs. In this work, I investigate a few theories that explain these phenomena, develop the corresponding mathematical formulations and employ these in a numerical reservoir simulator to demonstrate their impact on flowing fluid compositions and GOR/CGR trends. My work in this thesis is centered around investigating the role of multicomponent Knudsen diffusion and multicomponent adsorption as well as Fick’s diffusion, surface diffusion and molecular diffusion effects. With these transport mechanisms, I show that a constant CGR/GOR trend may be achieved with varying produced fluid compositions by allowing more rapid transport of lighter hydrocarbon components compared to those of a higher carbon number. I demonstrate this effect with a synthetic case study as well as with a field-scale case study. Although this work is the first such effort to quantify multicomponent flows in liquids-rich shales, the discussion in this thesis does not include experimental verification of the results. To that end, I also provide a few recommendations for experimental work to be performed to confirm the observations provided in this thesis.