A Well Productivity Model for Multi-Layered Marine and Continental Transitional Reservoirs with Complex Fracture Networks.

Using the typical characteristics of multi-layered marine and continental transitional gas reservoirs as a basis, a model is developed to predict the related well production rate. This model relies on the fractal theory of tortuous capillary bundles and can take into account multiple gas flow mechanisms at the micrometer and nanometer scales, as well as the flow characteristics in different types of thin layers (tight sandstone gas, shale gas, and coalbed gas). Moreover, a source-sink function concept and a pressure drop superposition principle are utilized to introduce a coupled flow model in the reservoir. A semi-analytical solution for the production rate is obtained using a matrix iteration method. A specific well is selected for fitting dynamic production data, and the calculation results show that the tight sandstone has the highest gas production per unit thickness compared with the other types of reservoirs. Moreover, desorption and diffusion of coalbed gas and shale gas can significantly contribute to gas production, and the daily production of these two gases decreases rapidly with decreasing reservoir pressure. Interestingly, the gas production from fractures exhibits an approximately U-shaped distribution, indicating the need to optimize the spacing between clusters during hydraulic fracturing to reduce the area of overlapping fracture control. The coal matrix water saturation significantly affects the coalbed gas production, with higher water saturation leading to lower production. [ABSTRACT FROM AUTHOR]