Abstract
Aiming at the problem that the production capacity of the NB19-X well in the NB19 block of the East China Sea was significantly lower than the design value of the development plan after its commissioning, this study systematically carried out the research on the diagnosis of reservoir damage mechanism and process optimization. Firstly, a productivity evaluation model for condensate gas reservoirs is established, with a calculation accuracy of the established productivity model being ≥ 90%. Through the analysis of the P-T phase state of the reservoir fluid, it was found that the amount of condensate precipitate from the formation accounted for only 0.6%-6%, confirming that condensate is not the main controlling factor. The scaling prediction based on the Scalechem4.0 software shows that the formation risk of CaCO3 scale is relatively high under the pressure reduction conditions of 135℃/5-50 MPa. However, the scaling amount in the near-well area is only 21.69 mg/L, indicating that the impact of scaling on production capacity is limited. The core discovery comes from dynamic contamination experiments: The permeability damage rate caused by cement slurry and perforating fluid reaches 74.4%-79.9%, among which the permeability after contamination by the mixed liquid is only 22.3%. To this end, an innovative low-harm working fluid system with the synergistic effect of "water lock removal - filter loss suppression - backflow promotion" was constructed: the surface tension of the completion fluid system was reduced to 28.00 mN/m; The filtration loss of the perforated liquid system API was reduced to 10mL, and the temperature resistance performance was improved to 140℃. Field applications show that the permeability damage rate of the optimized completion fluid has dropped to 63%, and the permeability recovery rate after backflow has reached 95%, which is 36% points higher than that of the conventional system.