Abstract

Worldwide increased demand for natural gas has challenged researchers to come up with more accurate reservoir description and reserve estimation for natural gas. This study uses a semi-analytical model to study pressure transient behavior of multilayered gas reservoirs. Gas flow though porous media is complicated by pressure dependent fluid properties, reservoir heterogeneities, high velocity effect, etc. High velocity effect causes additional pressure drop at the wellbore which is a function of flow rate, fluid and/or rock properties very close to the wellbore. As a result of drilling, rock properties, such as porosity and permeability, in the vicinity of the wellbore are affected. Moreover, large pressure gradient very close to the wellbore causes pressure dependent gas properties vary in the radial direction. Using a semi- analytical model this paper studies transient gas flow behavior through a multilayered reservoir. Both crossflow and commingled layer situations have been considered. In this study, different schemes for calculating high velocity effects have been studied and evaluated. For the same amount of skin, both thin skin and finite damaged zone responses have been compared, It has been observed that for the same amount of skin, finite damaged zone and thin skin responses can be significantly different for gas reservoirs. Effect of permeability, layering, and different outer boundary conditions have also been studied.

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