Abstract:

The Dina-2 Gas Reservoir, a large-scale edge-water tight sandstone gas reservoir in the Tarim Basin, exhibits strong reservoir heterogeneity, with natural fractures critically governing its high productivity and water invasion dynamics. Fracture characterization is pivotal for deciphering water invasion mechanisms and optimizing water control strategies. This study integrates geological data including core samples, thin-section analysis, and image logging to evaluate the static geological attributes of natural fractures, while production dynamics such as water and gas rates and pressure data are analyzed to assess multi-factor impacts on water influx. By applying the Analytic Hierarchy Process, controlling factors are systematically prioritized, revealing that tectonic fracture morphologies, classified as shear fractures and tensile fractures predominantly filled with calcite followed by quartz and clay minerals yet displaying significant apertures,dominate water invasion behaviors. Production wells are categorized into four distinct types based on dynamic performance: early-stage violent water-flooded wells, late-stage violent water-flooded wells, water-producing wells, and water-free wells, each exhibiting unique production trends. Integrated evaluation of structural position, faults, interlayers, matrix properties, and fractures identifies fractures as theprimary controlling factor, with faults, interlayers, and matrix acting as secondary contributors, while structural position shows negligible influence. A comprehensive water invasion evaluation index is established via the Analytic Hierarchy Process, underscoring the dual role of complex fracture networks in enhancing gas productivity and exacerbating water breakthrough risks. Three water invasion patterns are proposed: dominant fracture-controlled, fault-fracture compartment-controlled, and fault-dominant fracture-sandbody composite types,collectively delineating the reservoir's water invasion mechanisms. These findings offer strategic guidance for developing analogous heterogeneous fractured tight sandstone gas reservoirs and provide critical insights for water invasion mechanism research and development evaluation in similar water-bearing gas reservoirs.

Key words: Tarim Basin, Kuqa depression, natural fractures, water invasion characteristic, water intrusion pattern