Enhancing the production capacity of natural gas hydrates (NGHs) is critical for its commercial development. Complex structure wells may efficiently increase drainage areas while enhancing exploitation efficiency. Based on the field data of China’s first offshore NGH test production, the numerical method was used to analyze the production performance of different complex structure well types by continuous depressurization production for 360 days under the preconditions of fixed effective completion length of 300 m and a pressure difference of 6 MPa. Results indicated that the complex structure well types deployed at the three-phase layer demonstrated superior production performance within 240 days of production; the DLW2 and HW2 well types stood out, with an average gas production rate Q_g reaching 43,333 m³/d and a specific production index J of 24.1. After 360 days of production, benefiting from multi-layer combined production, the Cluster vertical well deployed at the multi-layer had the best production performance, with an average Q_g of 34,444 m³/d and a J-index of 19.1. The research results provided insights into the complex structure well-type selection strategy for NGH depressurization in this sea area.

Stepwise depressurization is an important depressurization strategy in the development of natural gas hydrates. This work numerically analyzes the effects of different depressurization gradients and constant pressure durations on gas and water production during stepwise depressurization extraction with a vertical well in the Shenhu Sea area hydrate reservoir of the South China Sea. The results indicate that stepwise depressurization can reduce water production and raise the gas-to-water ratio in the early stages of production while ensuring cumulative gas output. When the vertical well is deployed at the model’s center with a completion length of 70 m and a constant pressure duration of 10 days, a depressurization gradient of 0.5 MPa, stepwise depressurization by 6 MPa, and continuous production for one year is achieved. Compared with direct depressurization, its cumulative gas production is 2.966 × 10⁶ ST m³, which only decreases by 2.94%. However, it maintains a higher gas-to-water ratio in the early stages of production. Considering factors such as engineering operability, cumulative gas output, and gas-to-water ratio, it is recommended to use a small pressure gradient and a medium constant pressure stabilization time for stepwise depressurization Stepwise depressurization can maintain a high gas-to-water ratio while ensuring gas production and reducing water production can alleviate sand production problems and improve economic efficiency. The understanding gained from this work has reference value for the development of similar hydrate reservoirs worldwide.

Natural gas hydrates (NGHs) currently lack economic feasibility; efficient exploitation methods must be continuously explored to increase their production capacity. Drawing on field data from China’s first offshore NGH trial production, a numerical simulation method was used to evaluate a comprehensive development strategy that combines a horizontal well with boundary sealing, near-wellbore stimulation, and step-wise depressurization to improve the recovery of Class 1 NGH reservoirs. The results indicated that boundary sealing has a strong enhancement effect: it inhibits water invasion and thus concentrates the energy for hydrate dissociation. The use of high-pressure water jets for near-wellbore stimulation generates highly permeable channels, greatly accelerating hydrate dissociation and gas flow; step-wise depressurization optimizes the production behavior by controlling water production. The combined application of these technologies significantly improves development performance, with cumulative gas production (V_g) increasing to 220.1% and the gas-to-water ratio (R_gw) increasing to 102.6% compared to the base case, providing an effective strategy for the development of Class 1 NGH reservoirs.

Improving the production capacity of natural gas hydrates (NGHs) is crucial for their commercial development. Based on the data of the first on-site testing production of NGHs in the Shenhu Sea area, numerical methods were used to analyze the production behavior of radial lateral well (RLW) and horizontal snake well (HSW) with different completion lengths when they deployed at different layers of the Class-1 type hydrate reservoir (with a fixed pressure difference of 6 MPa and continuous production for 360 days). The results indicate that compared with the single vertical well production, RLW and HSW can effectively increase production capacity by enlarging drainage area and the productivity is directly proportional to the total completion length. The RLW and HSW deployed at the three-phase layer (TPL) have optimal mining performance within a 360-day production period. Different to the previous research findings, during a short-term production period of 360 days, regardless of the deployment layer, the overall production capacity of HSW is better than RLW’s. The total gas production of HSW-2 circles well type is about four times that of a single vertical well, reaching 1.554 × 10⁷ ST m³. Moreover, the HSW-1 lateral well type stands out with an average Q_g of 3.63 × 10⁴ ST m³/d and a specific production index J of 16.93; it has the highest J-index among all well types, which means the best mining efficiency. It is recommended to choose the HSW-1 circle well type, if the coiled tubing drilling technique is used for on-site testing production of NGHs in the future. The research results provide insights into the potential applications of RLW and HSW in this sea area.

Efficient development of marine natural gas hydrates (NGHs) remains challenging. Employing depressurization combined with complex structured wells and reservoir stimulation techniques is one of the key approaches to enhancing production. This study aims to theoretically evaluate the production response of different lateral layouts of multilateral wells under the conceptual condition of an idealized boundary sealing for the depressurization exploitation of Class 1 hydrate reservoirs. Based on data from China’s first offshore trial production, a numerical simulation method was used to systematically compare the development performance of various lateral layouts integrated with boundary sealing. Under the idealized modeling scenario, the simulation results indicate that the low-permeability barrier formed by boundary sealing can significantly suppress water invasion, promote pressure propagation, and thereby improve productivity. More importantly, optimizing the lateral layout can further enhance gas production performance. Under boundary sealing conditions, Case 8B with six downward-deployed laterals, compared to Case 1A without sealing and with six laterals in a planar staggered layout, its cumulative gas production (1733.75 × 10⁴ m³) was 2.08 times that of Case 1A (831.68 × 10⁴ m³), and its gas-to-water ratio (327.64) was 1.62 times that of Case 1A (202.09). This indicates that under boundary sealing conditions, lateral layout is one of the key levers to improve productivity. Under the modeling assumptions of this work, the research findings can provide a theoretical reference for evaluating the development of Class 1 hydrate reservoirs with multilateral wells where boundary sealing is considered.