| More and more nature gas will be demanded along with the society attach importance to environment protection very much now. While most of reservoirs have layered characteristics because of different deposition of formations comes into being in a different geologic period. One hand physical properties of each layer including permeability, porosity, and geometry size are various probably; on the other hand many wells are producing together with many layers in oil fields. During operation, productivity from multi-layer production is much less than that of the separate zone cases. This phenomenon is different from engineer's intuitive image, and they are frequently puzzled by such phenomena. Results from both study on characteristics of fluid unsteady flow in layers and analysis of well deliverability can be helpful for us to present practicable interpretation, to choose reasonable drawdown pressure and to perform reasonable production and injection prorating for wells. It has very importance for guiding exploitation of layered reservoirs. In the paper, a primary mathematical model is presented in an n-layered and circular bounded gas reservoir. The model has been solved in the condition of either constant flow rate or constant bottom pressure in Laplace domain. Effects of major parameters on productivity are discussed so as to optimize gas well production. General methods for solving the mathematical model are involved as Duhamel superposition principle, Laplace transformation, Bessel functions and Stehfest numerical inversion technique in this paper. Characteristics of the mathematical model are expressed in detail as typical curves, and key conditions for the model's application are expatiated in the text. Results from the paper may lift the study art of layered gas reservoirs to a new level, and can offer better theory and application method for oil/gas field. |
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