川西坳陷须三段致密砂岩气藏源储特征及成藏模式

川西坳陷须家河组致密气藏已成为拓展油气勘探、发现新储量的重要领域，致密气藏发育特征及其成藏机理成为目前亟需解决的关键科学问题之一。运用地球化学、地球物理和沉积学等分析方法，对须三段源储特征及成藏模式进行了系统分析，对高效烃源岩和优质储层进行了判别和预测，厘定了致密气藏成藏期次和成藏模式。得出以下结论:①须三段发育成熟-高成熟湖相烃源岩，以Ⅲ型干酪根为主，局部偶见Ⅱ₂型干酪根。发育于须三下亚段最大湖泛面附近，泥页岩体积分数在65%以上或者单层厚度较大、且1.50% ≤ w（TOC）≤ 10%时，属于高效烃源岩。②基于砂岩粒度中值识别出4期（S1，S2，S3和S4）优质储层，都属于低孔低渗-特低孔特低渗致密储层，中砂-细砂，粒度分布范围为0.5~0.062 5 mm，厚度一般5~10 m。主要发育于三角洲前缘和前三角洲。③烃源岩生排烃时间持续较长，中侏罗世开始生烃，一直持续至晚白垩世；从晚侏罗世开始排烃，早白垩世达到高峰。优质储层经历早期天然气持续充注和晚期凝析气充注，天然气充注时间要早于凝析气充注时间。形成了"断层垂向输导，先聚集后致密，晚期改造调整"的致密气藏成藏模式。 

Characteristics of reservoir-source rock and hydrocarbon accumulation model of tight sandstone gas reservoirs in the third Member of Xujiahe Formation in western Sichuan Depression

The tight gas reservoirs of the Xujiahe Formation in western Sichuan Depression have become an important field for expanding oil and gas exploration and discovering new reserves.The development characteristics of tight gas reservoirs and their accumulation mechanism have become one of the key scientific problems that need to be solved urgently. Applied geochemistry, geophysics and sedimentology analysis methods, systematic analysis of the source and reservoir characteristics and accumulation model of the Xu-3 Member was conducted, and the high-efficiency source rocks and high-quality reservoirs were identified and predicted. The accumulation period and accumulation mode were determined.The following conclusions were drawn: ①The lacustrine source rocks in the mature and highly mature stage of the Xu-3 Member in western Sichuan Depression are dominated by type Ⅲ kerogen, and occasionally type Ⅱ₂ kerogen.It is developed as a high-efficiency source rock when it is developed near the largest lake flooding surface in the lower sub-segment of Xu-3, with shale content above 65% or a single layer with a large thickness and requiring 1.50% ≤ TOC ≤ 10%.②According to the median value of sandstone grain size, the 4th stage (S1, S2, S3 and S4) high-quality reservoirs were identified, which belonged to low-porosity and ultra-low-permeability-ultra-low-porosity and ultra-low-permeability tight reservoirs. Reservoir space is dominated by secondary pores, micropores and microfractures.Most developed in the front edge of the delta and a small amount developed in the front delta.The particle size distribution range is 0.5-0.062 5 mm, the thickness is generally 5-10 m.③The hydrocarbon generation and expulsion time of the Xu-3 Member source rock in western Sichuan Depression lasted longer, and the Middle Jurassic began to generate hydrocarbons until the end of the Early Cretaceous; the Late Jurassic began to expel hydrocarbons and reached a peak at the end of the Early Cretaceous.High-quality reservoirs experience early natural gas continuous charging and late condensate gas charging.The natural gas charging time is earlier than the condensate gas charging time.The accumulation mode of tight gas reservoirs in the Xu-3 Member is "vertical fault transmission, first gathering and then dense, and later transformation and adjustment".