桂中坳陷桂中1井沥青成因及油气成藏模式

Bitumen genesis and hydrocarbon accumulation pattern of Well Guizhong-1 in Guizhong Depression

采用GC、GC-MS、稳定碳同位素、包裹体以及沥青反射率等分析测试技术,对桂中坳陷桂中1井储层固体沥青进行了系统分析,并对其来源及成因等进行了探讨。基于其成因特点,对桂中1井油气藏主要破坏因素进行了剖析,并结合区域研究成果,对桂中坳陷油气藏主要破坏因素进行了系统分析,进而探讨了桂中坳陷油气成藏模式。综合研究表明,桂中1井储层固体沥青来源于中下泥盆统泥质烃源岩,为早期油藏原油高温热裂解形成的焦沥青。桂中坳陷油气藏主要破坏因素有:早期油藏的深埋导致原油裂解为焦沥青和甲烷;后期的构造抬升剥蚀造成"异常高压"气藏压力系统破坏;断裂导致盖层封闭性变差以及岩浆/成矿热液对其附近的油气藏产生严重破坏。此外,天然气扩散、微渗漏作用等也可成为桂中坳陷油气藏遭受破坏的重要因素。因此,桂中坳陷地层保存相对完整、断裂欠发育、岩浆活动影响较小的中西部地区是桂中坳陷有利油气勘探区。

The reservoir solid bitumen of Guizhong-1 Well in Guizhong Depression of the middle Guangxi Province were analyzed by means of GC,GC-MS,stable carbon isotope,fluid inclusion analysis and bitumen reflectance measurement techniques.The origin and genesis of the solid bitumen in reservoir of Well Guizhong-1 in Guizhong Depression were discussed.On the basis of the origin characteristics of solid bitumen,the main destructive factors for the oil and gas reservoirs were analyzed.In combination of the regional research results,the main destructive factors for the reservoirs of Guizhong Depression were discussed.The potential reservoir-forming pattern of Guizhong Depression was investigated on the properties of reservoir destruction and preservation.The research result demonstrates that the solid bitumen in Well Guizhong-1 comes from the argillaceous rock of the middle-lower Devonian and is the pyrobitumen resulted from oil cracking at high geothermal temperature in the early pools.The main constructive factors for the reservoir in Guizhong Depression include the pyrobitumen and methane cracked from oil of the deeply buried pools in the early stage,the broken pressure systems of oil-cracked gas pools with abnormal overpressure caused by the later structure uplifting and strata denudation,the poor sealing property of the cap rock caused from fractures and faults,and the serious impact of oil-gas pools caused by the magma or hydrothermal ore-forming solution.Moreover,the diffusion and microseeping of natural gas in the pools is also the possible constructive factors of reservoirs in Guizhong Depression.So,the central and western areas of Guizhong Depression with the integrated strata,fairly poor fractures and faults and little magma activities are the favorable plays for hydrocarbon exploration.