Hydrate Formation Risk from the Gas Production Flow: Combined 2D Convergent Flow and Joule-Thomson Effect

Summary

Hydrate formation risk is caused by Joule-Thomson effect (JTE) under gas flow, when natural gas hydrate and shallow gas are exploited by depressurization method. However, the flow of gas from the reservoir to the wellbore is a process of gradually decreasing cross section, and experiments rarely consider the JTE under converging flow channels, making it difficult to accurately assess the risk. Using a self-developed 2D experimental device, we study the hydrate formation risk under different water saturations, reservoir depths, and production radii in this work. The results show that the 2D experiment phenomenon was closer to the actual reservoir than the 1D experiment. Moreover, water saturation had a significant impact on the temperature drop rate and the location of the lowest temperature point (LTP). The cooling effect at 20% water saturation is greater than that at 0% and 40%. As water saturation increases, the LTP moves away from the wellbore to 54 cm. The decrease of water saturation during the experiment also caused the LTP to approach the wellbore. The deeper the reservoir depth, the smaller the temperature drop required to form hydrates, making it more necessary to prevent the hydrate formation risk. Even with a production pressure differential as low as 2 MPa, the reservoir with 15.5 MPa had the risk of forming gas hydrate over a wide area around the wellbore. When the production radius was expanded from 1.9 m to 2.5 m, the temperature drop around the well was reduced by 30%. The results provide a reference for preventing hydrate formation around the wellbore during depressurization production. It is recommended to use a small pressure differential at the beginning of production and gradually increase the production pressure differential as the production progresses.