Visual downhole throttling simulation experiment and nozzle flow model evaluation for water-producing gas wells with ultrahigh pressure

Downhole throttling can effectively prevent hydrate generation at wellhead, simplify surface processes and reduce costs. However, when this technology is applied in water-producing gas wells with ultrahigh pressure, the mutual influence between gas-liquid two-phase flow and nozzle flow may lead to significant discrepancies between the daily gas production and the designed values for some wells. Accurately predicting the flow rate and pressure drop of gas and liquid through downhole throttler is crucial to process design. To address this issue, one study was conducted based on a constructed visualization experimental apparatus to perform downhole throttling simulation experiments. The dynamics of gas-liquid two-phase nozzle flow under different flow patterns was analyzed. Data were divided based on the upstream flow pattern before the throttler, and the performance of four commonly used engineering nozzle flow models under different flow patterns was evaluated. The research results show that among the mathematical models used to predict mass and flow rate for slug flow, turbulent flow and annular flow, it is recommended to apply Ashford model (with correlation coefficient R² is 0.92), Sachdeva model (with correlation coefficient R² is 0.80), and Al-Safran model (with correlation coefficient R²is 0.96), respectively. To verify the accuracy of the model evaluation results. Well Shuangtan 8 was selected for field application. The depth of the downhole throttler was determined to be 3 000 meters, the flow pattern was judged to be turbulent flow, and the calculated nozzle diameter was 5.3 mm according to the selected Sachdeva model. The evaluation results of the model can provide theoretical basis and guidance for the design of downhole throttling technology in water producing gas wells, and have certain promotion value.