Working Fluid-Induced Formation Damage Evaluation for Commingled Production of Multi-Layer Natural Gas Reservoirs with Flow Rate Method

Conventional industry standards (CIS) or methods that rely on the permeability indicator are incapable of directly and precisely evaluating the working fluid damage in multi-layer reservoirs as a whole via Darcy equation and fail to represent the characteristics of gas flow through the reservoir under an in-situ stress state. In this study, we proposed a flow rate method that was based on theoretical derivation and test parameter optimization to overcome these deficiencies. The rationality of the proposed method was verified through comparative experiments and field case analyses. Results showed that the instantaneous flow rate index was almost equivalent to permeability in characterizing the degree of working fluid damage. Comparing the classification of damage degree with the skin factor, the CIS method was only with a conformity of 25%, while the instantaneous flow rate method was as high as 90%. Although the practicality of the cumulative flow rate index has not been proven, it could be used to comprehensively measure the production loss over a specified period. In conclusion, the proposed flow rate method can effectively reflect the actual reservoir properties and accurately evaluate the overall damage of commingled production reservoirs, then providing better guidance for future development plans.