南羌塘坳陷布曲组油藏带特征及空间演化规律

Characteristics and evolution of oil reservoir zones of Buqu Formation in the southern Qiangtang Depression

南羌塘坳陷大面积出露中侏罗统布曲组油藏带,为了了解布曲组油层地下隐伏特征,查明油气富集规律,根据油藏带地质产状、发育层位、沉积序列及空间分布等特征,结合油藏带形成时的古地理格架,研究了油藏带的形成与演化过程。结果表明,油藏带平面上集中分布于隆鄂尼、昂达尔错和赛仁等3个区块,并以东西向稳定线状展布为特征,成层性好;油层内部可见大量礁滩相残余构造,常与介壳灰岩、生物碎屑灰岩、鲕粒灰岩及砂屑灰岩相伴生,显示出典型台地边缘礁滩相沉积特征,其形成与演化受沉积相带和海平面升降变化的控制:在布曲组沉积早期,台缘浅滩位于南羌塘坳陷南缘塞仁—昂罢存咚一带;随着海平面的上升,沉积相带发生退积,向北依次形成晓嘎晓那—日尕尔保、扎仁—冬浪啪和日阿梗—噢纵等一系列线状分布的台地边缘相沉积;在布曲组沉积晚期,由于海平面下降,台地边缘礁滩相沉积向南进积扩展,形成隆鄂尼区块上部礁滩相沉积。

Oil reservoir zones of Middle Jurassic Buqu Formation are widely exposed in southern Qiangtang Depression. Based on the geological occurrence, stratigraphic sequence, sedimentary facies and space distribution of oil reservoir zones, combined with paleogeography framework, the subsurface characteristics and evolution of the oil reservoir zones were studied. The results show that the oil reservoir zones developed in three blocks： Long＇ eni, Angdaercuo and Sairen, respectively, and they are characterized by east- west stable linear distribution and good stratification. A large number of reef bank facies residual structures can be seen in the reservoir, and they are associated with coquinite, bioclastic limestone, oolitic limestone and calcarenite. These oil reservoir zones are controlled by platform margin facies and the sea-level changes. At the early Buqu stage, the reef and shoal facies deposited along platform margin from Sairento Angbacundong. At the middle Buqu stage, with the rise of sea level,a series of parallel and linear platform margin facies formed by retrograding northward in Xiaogaxiaona-Rigaer- bao, Zharen- Donglangpa and Riagen- Aozong. At the late Buqu stage, the progressive reef and bank facies ad- vanced southward gradually along the platform margin with the drop of sea-level, and widely developed in Long＇ eni block.