Abstract: The Lower Cambrian Qiongzhusi Formation shale gas is the second shale reservoir capable of large-scale development after the Silurian Longmaxi Formation shale gas. The Qiongzhusi Formation in Ziyang Area is generally buried at depths greater than 4 500 m, with some exceeding 5 000 m, and belongs to a typical ultra deep shale gas reservoir. Unlike the Longmaxi Formation's deep shale gas, the fracturing of Qiongzhusi Formation's shale is faced with difficulties of ultra high pressure and low complexity fractures due to its high stress gradient and under-developed large-scale fractures. This article proposes a multi domain fracture fracturing technology to address the above difficulties, based on geological multi-scale fracture identification and engineering corresponding fracture multi domain communication. By using multiple methods to finely characterize and identify micro lithological cracks, honey points can be found in sweet spots. Seismic-geological-engineering integrated simulation software carries out full 3D numerical modeling to track hydraulic fracturing propagation, and variable density segmented clustering and 22 m$^3$/min communication of wide area large-scale cracks are proposed. Based on the complexity experiment of the physical model, multiple temporary blockages+pump stop temporary blockages are proposed to promote the expansion of lithological microcracks, matched with 140 MPa and high-strength construction scale, breaking through the barrier and support of ultra deep, multi-type, and multi-domain crack channels. The successful application of this technology in Well ZY2 has achieved a breakthrough in ultra deep shale gas fracturing, creating multiple records in construction displacement, construction scale, and temporary plugging strength, effectively ensuring the exploration breakthrough of the Qiongzhusi Formation in Ziyang Area and providing new ideas for ultra deep shale gas fracturing technology in the region.

Key words: ultra deep shale gas, Lower Cambrian, seismic-geological-engineering integrated simulation, Qiongzhusi Formation hydraulic fracturing, multi-domain fractures