寒武系烃源古油藏油裂解气特征及成藏条件

在寒武系为母源的气藏中,普遍存在的固体沥青、25-降藿烷、氮气等三种物质,实际是古油藏残余油裂解的产物。25-降藿烷一般与氧化—降解油有关,氮气来自油藏水洗时溶入的大气,二者共同反映古油藏经历的抬升破坏作用。寒武系烃源一般经历过两次成藏:加里东—海西期形成“油藏”,燕山—喜马拉雅期裂解为“气藏”。寒武系油裂解气成藏的地质条件是:古构造聚油、后期改造适度、叠合盆地增熟、断层作为油气运移通道等。围绕加里东—海西期古油藏寻找原生、次生油裂解气是今后寻找寒武系来源油气的重要途径。     

羌塘盆地昂达尔错白云岩古油藏地质特征及成藏条件

昂达尔错白云岩古油藏位于羌塘盆地南羌塘坳陷,是羌塘盆地规模最大的古油藏带,对该区油气勘探具有重要意义。依据铸体薄片、储层物性、沥青族组分分析,剖析了白云岩古油藏地质特征。分析结果表明,昂达尔错古油藏的储集体可归类为低孔—低渗型到中孔—中渗型储层,为较好储层类型;其石油族组分呈现饱和烃含量低、非烃+沥青质含量高的特征,为芳香沥青型、芳香环烷型石油。划分出两套生储盖组合,其中的下侏罗统曲色组—中侏罗统布曲组组合为较好的生储盖组合类型,具有较好的勘探远景。认为古油藏在晚侏罗世成藏,在喜马拉雅期遭受逆冲破坏。     

桂中坳陷海相地层油气成藏与热作用改造

桂中坳陷是在加里东运动基础上形成的晚古生代海相大型沉积坳陷,已演化成为由上古生界和三叠系充填的残留盆地,其中泥盆系深埋地腹,是主要的勘探目的层系。桂中1井揭示泥盆系—石炭系具有两套生储盖组合,钻遇了气测异常、油迹砂岩、固体沥青等三类油气显示,其中泥盆系沥青显示井段累计709m。桂中坳陷古油藏(沥青)主要来源于中—下泥盆统塘丁组和罗富组泥岩。桂中1井和南丹大厂储层固体沥青为运移/成藏的油气发生热裂解而形成的焦沥青。桂中1井经历了两期油气充注,第一期为印支期前的主力生烃期,第二期(晚期)为燕山期—喜马拉雅期,以紧邻油气显示层的可溶烃类为代表。经历了三期油气改造:第一期为印支期前的油气藏经历了地层沉降增温的热裂解作用而演化为固体沥青和甲烷天然气,第二期为燕山晚期岩浆活动导致的更高温度的热蚀变作用,第三期为喜马拉雅期构造抬升的改造或破坏作用对上泥盆统油气藏的影响。晚期成藏的天然气应是下一步的勘探方向。桂中坳陷西部地层保存相对完整(目的层深埋),断裂和岩浆活动相对不发育,可能更有利于天然气的聚集和保存。     

皖南—浙西下古生界碳沥青成因及南方海相“有效烃源岩”问题探讨

赋存于皖南—浙西的固体碳沥青分为古油藏裂解碳沥青和古油藏破坏次生充填碳沥青两种类型 ,阐明了两类碳沥青的不同成因机制。重新认定了浙西“康山沥青脉”为碳沥青而不是泥岩。论证了皖南、浙西碳沥青的烃源为下寒武统、中—上奥陶统至下志留统、中—上寒武统等。认为加里东运动—广西事件期间是下扬子盆地相区以下寒武统黑页岩为烃源的油藏形成和部分破坏的主要时期。针对南方的油气勘探 ,提出了只有在晚期成藏中作出贡献的源岩才是“有效烃源岩”的新概念。     

The source of highly overmature solid bitumens in the Permian coral reef paleo-reservoirs of the Nanpanjiang Depression

Solid bitumens occur extensively in Permian coral reefs of the Nanpanjiang Depression. Both potential source rocks and solid bitumens in the study area are highly overmature and have similar bulk carbon isotope values. It is difficult to perform an oil–source rock correlation study in this area based on only regular molecular geochemical methods and bulk carbon isotope values. Thus the covalently bound biomarkers released from solid bitumens and source rock kerogens by catalytic hydropyrolysis (HyPy), together with the geological settings, were taken into account in this oil–source rock correlation study. The distribution characteristics of covalently bound biomarkers suggest that the major source rock of the Longlin paleo-reservoir (in the midwest of the depression) solid bitumen should be the Middle Devonian mudstone, whereas the source rock of the Ziyun paleo-reservoir (in the north of the depression) solid bitumen should be the Lower Permian source rock. However, solid bitumens in the Ceheng and Wangmo paleo-reservoirs (in the middle of the depression) may be mainly sourced from the Middle Devonian source rock, but partly from the Permian source rock. Our bitumen–source rock correlation results are also supported by the petroleum geological settings of the study area, which indicate that the filling of those paleo-reservoirs was controlled by the matching of hydrocarbon generation and trap formation. Basically, the timing of hydrocarbon generation of the Middle Devonian source rocks matches well with the formation of Permian coral reef traps in the middle and midwest portions of the depression, but it is earlier than the formation of the Permian coral reef trap in the north of the depression. We show that our oil–source rock correlation study based on covalently bound biomarkers can provide reliable information for petroleum system analysis when highly overmature strata in South China are involved.