Main Controlling Factors and Three-Dimensional Development Potential of Deep to Ultra-Deep Shale Gas in the Luzhou Area, Sichuan Basin

The reservoir quality and gas-bearing properties of the Wufeng Formation–Longmaxi Formation shale vary significantly across different structural units in the Luzhou area of the Sichuan Basin. The mechanisms of shale gas enrichment, tectonic controls, and accumulation models are critical determinants of the potential for three-dimensional (3D) development. Integrating data from core analyses, logging interpretation, focused ion beam scanning electron microscopy (FIB-SEM), and high-resolution core scanning, this study investigates the control exerted by fracture development and tectonic activity on shale gas enrichment and preservation. A conceptual model for shale gas enrichment and accumulation is established, and the potential for 3D development of deep shale gas in the Luzhou block is evaluated. The results indicate that: (1) Reservoir heterogeneity in deep shale gas plays is jointly governed by reservoir space characteristics, diagenesis, structural position, tectonic evolution, and fracture-fluid activity. Organic-rich siliceous shales retain favorable reservoir properties, characterized by an organic matter (OM) pore-dominated pore structure, relatively high porosity and permeability, and good gas-bearing potential due to overpressure preservation. (2) Structural style exerts dominant control over the gas-bearing variability. Synclines are significantly more favorable than anticlines, with free gas migration governing the enrichment pattern. The cores and flanks of synclines form zones of high gas content due to structural integrity, whereas the gas content decreases in anticlinal areas near faults. (3) Shale gas enrichment relies on the synergistic configuration of “high organic carbon content + high-quality pore reservoir space + robust structural preservation conditions.” Well L213 in the syncline core, distant from faults, exhibits good structural integrity and preservation conditions. Free gas from structurally lower positions migrates laterally toward the flanking anticlines, with a portion preserved in the syncline flanks. Concurrently, microfractures enhance reservoir storage and permeability, rendering syncline structures more conducive to shale gas preservation. (4) The high-quality shale succession in the study area is thick and laterally continuous, characterized by “vertical stacked pay zones.” This provides an excellent geological foundation for 3D development. By optimizing the well trajectory design and employing efficient fracturing technologies, such as “intensive fracturing” combined with temporary plugging and diversion, full and balanced utilization of vertically stacked sweet spot reservoirs can be achieved, significantly enhancing the single-well productivity and estimated ultimate recovery (EUR).