Modeling of stress-lithofacies synergistic fracture for buried hill granite in Songnan low uplift, Qiongdongnan Basin

The granite buried hill reservoirs in the Songnan Low Uplift of the Qiongdongnan Basin exhibit considerable hydrocarbon exploration and development potential. However, they feature complex pore-fracture pattern and strong fracture heterogeneity, posing great difficulties for fine reservoir characterization and quantitative modeling. Taking the buried hill reservoir of the YL-A gas field as the case, a systematic investigation was conducted on the fracture genetic mechanisms and quantitative reservoir modeling based on core, logging, and seismic data. Results indicate that the development of multi-stage and multi-type fractures in granite buried hills is jointly controlled by lithomechanical properties and multi-phase tectonic evolution. Syenogranite and monzogranite with high brittleness are the most favorable lithologies for fracture development. Progressive tectonic reworking during the Indosinian, Yanshanian, and Himalayan orogenies resulted in a complex and well-connected fracture network in the study area. Significant variations in paleostress intensity and orientation during different tectonic stages dominated the spatial distribution and development scale of regional fractures. The igneous lithofacies show strong spatial heterogeneity, and the elastic parameter μ×ρ can effectively distinguish different lithologies and accurately characterize spatial differences in mineral composition and mechanical behavior of buried hill rocks. The proposed stress-lithofacies coupled modeling integrates macroscopic tectonic constraints and microscopic lithological mechanical differences, achieving reliable characterization of fracture seepage heterogeneity. The modeled results are well consistent with field production data. This study provided new geological understanding and technical references for the fine evaluation and effective development of fractured igneous buried hill reservoirs in similar basins.