Abstract: The Permian marine shale is widely distributed in (northeastern) Sichuan Basin, and the high-yield gas flow has been obtained in Well Tiebei 1 L-HF, with a daily gas rate exceeding 30×10⁴ m³ at a depth of greater than 5000 m in the northeastern basin, marking a major breakthrough in the exploration field of the ultra-deep shale gas. Based on the latest exploration results of Well Tiebei 1 L-HF, the regional sedimentary characteristics of the Permian Dalong Formation in the study area has been analyzed, and the geological characteristics of Dalong Formation shale gas has been studied. In addition, main controlling factors for shale gas enrichment and high-yield production in ultra-deep formation has been discussed, clarifying the further exploration orientation of Dalong Formation in the northeastern Sichuan Basin. The comprehensive study and evaluation show that the ultra-deep shale in the Permian Dalong Formation in the northeastern Sichuan Basin has the typical geological characteristics of “one multiplicity, three highs and one medium”, namely the development of multiple shale facies types,high TOC, high gas content, high brittleness and medium porosity. The reservoir space of Dalong Formation ultra-deep shale is dominated by nanoscale organic pores and microfractures, and the coupling distribution of “organic pores + microfractures” significantly enhances physical properties and fracability of ultra-deep shale gas reservoir. The main controlling factors for the enrichment and high-yield production of ultradeep shale gas have been identified, that is, the development of contiguous carbon-rich lithofacies is the foundation, the coupling control of organic pores and microfractures over reservoir is the key, and favorable preservation conditions (ultra-high pressure sealing) are the external manifestation of gas enrichment. By adopting seismic imaging technology for the sub-salt steep structures and reservoir stimulation method of “175 MPa equipment for enhanced net pressure, multi-size grading strong proppants, and high-viscosity/high pumping rate for transverse fracture penetration”, it has achieved an 100% drilling rate of sweet spots and large-scale effective reconstruction of ultra-deep shale gas reservoir. This breakthrough marks that the shale gas exploration in China has stepped into the field of ultra-deep formation. It further confirms that there are abundant shale gas resources in ultra-deep formations in Sichuan Basin, which is an important replacement field for natural gas exploration and development in China.

Key words: Sichuan Basin, Northeastern Sichuan Basin, Dalong Formation, ultra-deep shale gas, enrichment and high-yield production;controlling factor, engineering technology, significance