呼和湖凹陷辫状三角洲的沉积特征和储集性能

Sedimentary Features and Reservoir Properties of a Braid Delta in Huhehu Depression

Huhehu depression covers an area of approximately 2640km~2. The Damoguaihe Formation, an upper Jurassic lacustrine sequence up to 1500m thick, mainly consists of braid delta deposits. The deposits are typified by an abundance of cross-stratification. The lithofacies and lithofacies assemblages of a braid delta display marked sedimentologic differences from allurial fan deposits. The braid delta deposits formed by the progradation of a braid river into the lake have a sheet geometry with high lateral continuity. Detailed examinations of petrography cathodoluminescence, SEM, and X-ray diffraction reveal the diagenetic features of the braid delta reservoirs. Diagenetic events principally involve mechanical compaction, quartz authigenesis, pore-lining smectite formation, pore-filing kaolinite formation, feldarspar overgrowth, pore-bradging illite formation, calcite precipitation, and chlorite authigensis. Diagenesis and sandbody microfacies, exercise control over reservoir properties. The braid delta reservoirs of shallow and moderate diagenetic zones exhibit moderate to high porosity and permeability.