滨里海盆地东部盐下成藏主控因素及勘探思路

滨里海盆地普遍发育一套下二叠统空谷阶盐岩层 ,是良好的区域性盖层 ,它把盆地分为盐上和盐下两大复合成藏组合。海西运动晚期 ,盆地东部地区断续、强烈的构造运动决定了地层空间展布、组合特点 ,控制了三个成藏带的形成 ,共发育三套成藏组合。盆地东部地区盐下油气藏规模、储量较大 ,大中型油气藏主要与石炭系两套海相碳酸盐岩层 (KT Ⅰ和KT Ⅱ )有关。在盆地东部发现的 10个盐下油气藏中 ,KT Ⅰ、KT Ⅱ产层的盖层均为其顶部泥岩层。下石炭统生物碎屑灰岩和下二叠统页岩是有效生油岩 ,分散有机质属混合类型。储层类型以孔隙型为主 ,溶洞型、孔洞型储层较发育 ,裂缝型储层偶尔发育 ;储层的次生改造作用非常重要。石炭系碳酸盐岩储层普遍分布 ,油气成藏主要受圈闭位置及其特点所控制。 90 %以上的失利探井是因为构造不落实 ,精确落实构造圈闭的具体位置 ,成为勘探的重中之重。

The Origin of Hydrocarbon Accumulation below the Lower Permian Salt Bed and the Prospecting in the East Part of Pre-Caspian Basin/

The wide-distributing Lower Permian Kungurian salt bed acts as a good regional seal cap in Pre-Caspian, on and beneath of which a multi-play lies respectively. The lower multi-play includes three plays which were developed during the continual intensive late-Hercynian orogeny in. the east part of the basin Reservoirs in these plays are wide in scale and hydrocarbon is rich in reserves. The large- and/or moderate-sized reservoirs are mostly relative with the both beds of Carboniferous marine carbonate rock, the target horizons, KT-Ⅰ and KT-Ⅱ. In the discovered 10 reservoirs below the salt bed, both the KT-Ⅰ and the KT-Ⅱpays are all covered by their overlying mudstone caps and the hydrocarbon in them are derived from the lower own Lower Carboniferous bioclastic limestone and the overlying Lower Permian shale. The organic matter belongs to mixed types. Porosity is developed and was secondarily reconstructed in these reservoirs. The ”Carbonate bocks-Reef (dolomitization)-Gypsum/Salt” has been ever regarded as the model of hydrocarbon accumulation and tectonics has been counted for acting as an minor role in Pre-Caspian Basin. Having Studied the geological setting and delimited the boundaries of plays by the influenced factors of hydrocarbon accumulation in this area, the author suggests that tectonic evolution is the major factor of controlling carbonate deposition, trap forming, and hydrocarbon accumulation. The 90 percent of failed wells were owing to drilling in uncertain structure locations so it is important that accurate drill sites must be offered for exploration.