Abstract:

The development of onshore low-permeability gas reservoirs has become relatively mature. In North America, efficient development has been achieved through technologies such as horizontal wells, hydraulic fracturing, and microseismic monitoring. In the Ordos Basin and Sichuan Basin in China, adaptive technical systems suitable for local geological conditions have been established through the introduction and re-innovation of technologies. However, the recoverable reserves per well generally remain low. In contrast, the development of offshore low-permeability gas reservoirs faces challenges such as high investment, limited platform space, multiple drilling constraints, and strict environmental requirements, leading to relatively slow progress. Offshore unconventional resources, especially low- and ultra-low-permeability natural gas, are gradually becoming important alternatives to conventional resources. In the Xihu Sag of the East China Sea, low-permeability gas reservoirs account for more than two thirds of the total resources. They are characterized by great burial depth, strong heterogeneity, and poor porosity and permeability conditions, making development challenging and requiring high economic efficiency. Since the development of low-permeability gas reservoirs in the Xihu Sag of the East China Sea began in 2006, significant breakthroughs have been made in the development of low-permeability gas reservoirs in the East China Sea over nearly 20 years of exploration. Through two stages of exploratory practice, a development model with "sweet spot prediction + efficient well types + reservoir protection" as the core has gradually been developed. A technical system tailored to the characteristics of low-permeability gas reservoirs in the Xihu Sag has been established, and the core driving force for transforming difficult-to-produce resources into economically viable production has been revealed. However, the large-scale development of these reservoirs in the East China Sea still faces three major scientific and technological challenges: deepening theoretical understanding, overcoming key technical barriers, and achieving cost-effective and efficient development. To address these issues, future research and development efforts should focus on the following three aspects: (1) strengthening fundamental research to deepen theoretical understanding and establish a high-success-rate system for geological reservoir evaluation and selection; (2) overcoming key technical barriers by developing more adaptable technologies and equipment systems for the development of low-permeability gas fields in offshore areas; and (3) improving development efficiency through establishing an integrated technical and management model that supports low-cost and efficient development of offshore low-permeability gas reservoirs, encompassing offshore engineering, drilling, gas production, transportation.

Key words: East China Sea, Xihu Sag, low-permeability gas reservoirs, development practices, offshore oil and gas, hydraulic fracturing