Enhancing marine shallow gas production through hybrid vertical and horizontal wells

Offshore shallow gas resources, once considered geological hazards, are now valuable unconventional energy sources. Preliminary tests in the Pearl River Mouth Basin show gas production rates of 55,000 m³/day, nearing commercial viability. However, optimizing extraction strategies remains a challenge due to vertical heterogeneity in the reservoirs, with alternating gas layers and low-permeability interlayers. This study proposes a stereoscopic exploitation model integrating horizontal and vertical wells. The horizontal well targets high-yield gas layers, while the vertical well ensures comprehensive extraction. Simulations reveal that with a 400-meter horizontal section, gas production reached approximately 88,000 m³/day after two years. This production level met the commercial requirements for shallow offshore gas fields. Notably, the horizontal well contributed 93% of the output during later stages. Gas production ranged from 2.70 × 10⁷ m³ to 6.07 × 10⁷ m³ over two years, depending on the horizontal well's positioning. Pressure distribution evolved from multi-peak to single-peak depletion, driven by the horizontal well. The distribution of interlayers caused varying levels of water invasion, with gas saturation damage ranging from 4.6% to 36.7%. The hybrid well strategy enhances efficiency, highlighting its broad applicability for developing heterogeneous shallow gas reservoirs.