Injectivity Assessment of Radial-Lateral Wells for CO 2 Storage in Marine Gas Hydrate Reservoirs

The carbon dioxide (CO 2 ) leak from conventional underground carbon storage reservoirs is an increasing concern. It is highly desirable to inject CO 2 into low-temperature reservoirs so that CO 2 can be locked inside the reservoir in a solid state as CO 2 hydrates. Marine gas hydrate reservoirs and surrounding water aquifers are attractive candidates for this purpose. However, the nature of the low permeability of these marine sediments hinders the injection of CO 2 on a commercial scale due to the low injectivity of wells with conventional completions. This study investigates the injection of CO 2 into low-permeability marine reservoirs through a new type of well, namely a radial-lateral well (RLW). A mathematical model was developed in this study to predict the CO 2 injectivity of the RLW. The model comparison shows that the use of RLW to replace vertical wells can improve CO 2 injectivity by over 30 times, and the use of RLW to replace frac-packed wells can increase CO 2 injectivity by over 10 times. A case study and sensitivity analysis were performed with field data from the South China Sea. The result of the analysis reveals that the injectivity of the RLW is nearly proportional to reservoir permeability, lateral wellbore length, and the number of laterals. The CO 2 injection rate is predicted to be 19 tons/day to 250 tons/day, which is 3 to 15 times higher than the injectivity of frac-packed wells. It is feasible to inject CO 2 into the low-permeability, low-temperature marine reservoirs at commercial flow rates. This work provides an analytical tool to predict the CO 2 injectivity of RLW in low-temperature marine reservoirs for leak-free CO 2 storage.