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

呼和湖凹陷是海拉尔盆地的一个次级负向构造,面积约2640km^2,凹陷内上侏罗统大磨拐河组厚达1500m,主要由辫状三角洲组成,辫状三角洲砂体含有丰富的交错层,缺乏沉积物重力流沉积,与冲积扇及扇三角洲在岩相及岩相组合上有明显的差异。由辫状河入湖所形成的辫状三角洲砂体,侧向连续性好,呈席状展布。这种储层的主要成岩事件有压实、石英加大和自生、蒙脱石生成、高岭石沉淀、长石加大和自生、伊利石形成、方解石沉淀和绿泥石形成。成岩作用和砂体微相对储层的储集性能起控制作用,处于浅成岩和中成岩带的辫状三角洲储集层具有中—高的孔隙度和渗透率。

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.