蓬莱9-1构造花岗岩古潜山大型油气田的成藏过程

摘要

目前国内针对燕山运动期中生代侵入的花岗岩潜山油气如何成藏且成藏规模之大的研究非常匮乏。该文主要采用岩心观察、薄片鉴定、指纹化石对比及油气盆地模拟等方法，对渤海海域蓬莱9-1构造花岗岩潜山的储层特征、油源对比及成藏条件进行了详细剖析，恢复了渤海蓬莱9-1构造花岗岩古潜山大型油气田的成藏过程，并建立成藏模式。根据花岗岩风化壳的风化程度，自上而下分为：砂-砾质风化带、裂缝带与基岩带，主要储集空间为溶蚀孔隙与微裂缝，风化壳储层发育厚度几十米，甚至达200多米。古潜山油源来自渤东南洼沙三段、沙一段或东营组烃源岩。储层发育区主要分布于风化壳的高部位，新近系馆陶组是潜山油藏有利的封堵层。古潜山油藏具有“下生上储顶盖的新生古储式组合”和“高压驱烃、断层不整合输导、油气仓储式成藏”的特点。%The granite buried hill weathering crust reservoir of Penglai 9-1 on the bulge of Miaoxibei in Bohai is a large scale oil and gas field firstly discovered in offshore China.However,the mechanism of hydrocarbon accumulation in granite buried hill in such a large-scale oilfield during the Yanshan movement is rarely studied. Therefore, different methods of core observation, thin section identification,fingerprint fossil comparison and hydrocarbon basin simulation are used to analyze the reservoir characteristics of granite buried hill,oil and source rock correlation and conditions of hydrocarbon accumulation,so as to restore the hydrocarbon accumulation process and construct the accumulation mode of Penglai 9-1 structure. According to the extent of weathering, granite weathering crust is divided from top to bottom into three parts:sand-gravel weathered zone,fracture zone and the bedrock zone respectively.The thickness of weathering crust varies from several tens of meters to even more than two hundred meters.It shows that the main reservoir space of oil and gas is dissolution pores and micro-cracks in the rocks and the oil source of buried hill comes from the first and third Groups of Shahejie Formation and Dongying Formation in the southern depression of east Bohai area.Favorable reservoirs are covered by seal rock of Guantao Formation of Neogene and mainly distributed in the high part of the weathering crust.The buried hill oilfield is characteristic of 3 layers structure with source rocks at the bottom,reservoir in the middle and cap rocks on the top,a combination of young source rocks in old reservoirs.The study proposes that high pressure drives hydrocarbon to migrate through fault-related unconformity and result in warehouse accumulation.