川西北双鱼石地区栖霞组储层成藏期次及流体演化

Stages of Hydrocarbon Accumulationand Fluid Evolution of Qixia Reservoir in Shuangyushi Area, Northwest Sichuan Basin, China

以岩心观察描述为基础,结合偏光显微镜薄片、阴极发光及流体包裹体等分析手段,探讨了川西北双鱼石构造栖霞组储层成岩和成藏期次及流体演化.结果表明,川西北双鱼石构造栖霞组上部储层整体为亮晶云质灰岩,可将其成岩矿物充填划分为四期,依次为早期微细晶方解石、重结晶的方解石、围岩孔洞中共生的石英钠长石和沥青、裂缝中充填的白云石和方解石.结合不同成岩阶段流体包裹体特征与埋藏史分析表明,二叠到中三叠纪研究区整体沉降接受沉积,埋深加大并受峨眉地裂伴随的热液作用影响,形成重结晶方解石,早中三叠-中侏罗纪下寒武统烃源岩达到生油高峰,使得第一期原油充注到栖霞组储层,随后二叠系中下部烃源岩在早侏罗-早白垩世达到生油高峰,即第二期原油充注.富硅热流体的充注形成石英和钠长石,同时由于埋深和热流体的改造,部分原油裂解生成沥青,古气藏开始逐步成藏.燕山晚期到喜山期龙门山地区在中生代中晚期经历了持续的逆冲构造变形,在构造裂缝充填白云石和方解石.裂缝充填方解石脉中捕获含甲烷包裹体和沥青包裹体,即古气藏随之调整,整体呈现早成藏晚调整的特点.

Based on drilling core observation, combined polarizing microscopic observation forthin section, cathodoluminescence and fluid inclusion analysis, this paper discusses hydrocarbon accumulation and fluid evolution of Qixia Formation in Shuangyushi structure in northwestern Sichuan. There sults show that the upper reservoir of Qixia Formation of Shuangyushi structure in northwest Sichuan is sparry cloud limestone, and its fillings of diagenetic mineral can be divided into four stages, including early fine crystalline calcite, recrystallized calcite, quartz and albite filled in early limestone holes,and dolomite and calcite filled in pore cracks. Combined with the characteristics of fluid inclusions in different diagenetic stages and burial history analysis, it is found that study area was settled and accepted deposition from Permian to Middle Triassic, recrystallized calcite was formed due to the increase of burial depth and hydrothermal action associated with Emei taphrogeny. The early-middle Triassic to middle Jurassic lower Cambrian source rocks reached the peak of oil generation, which made the first stage of oil charged into Qixia Formation reservoir. Then the middle and lower Permian source rocks reached the peak of oil generation in the Early Jurassic and Early Cretaceous, that is, the second stage of oil charging. Quartz and albite were formed due to the charging of silica-rich hydrothermal fluid. At the same time, due to the burial depth and the transformation of hydrothermal fluid, part of the crude oil cracked into bitumen, and the ancient gas reservoir began to form gradually. The Longmenshan area experienced continuous thrust deformation in the middle and late Mesozoic from late Yanshanian to Himalayan, structural fractures were filled with dolomite and calcite.Methane and asphalt inclusions were captured in the veincalcite, and the ancient gas reservoirs were adjusted accordingly, which indicated the characteristics of early accumulation and late adjustment.