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。

Geochemical Characteristics and Geological Condition of Cambrian Oil-cracking Gas in Paleoreservoir

The general existence of the subsidence such as solid bitumen, 25-norhopane in bitumen and abundance nitrogen gas in a gas paleoreservoir means that in fact they are the products from residual oil in cracked process. The 25-norhopane is generally associated with oxidation and degradation of petroleum and the abundance nitrogen was from atmosphere dissolved in oil-reservoir as washing, either of which reflected the ever raising and destruction of paleo-reservoir. The accumulations of hydrocarbon from Cambrian source rock generally happened twice, the first as oil was during Caledonian to Hercynian period and the second as cracking gas was during Yanshanian to Himalaya period. The available geological conditions of oil-cracking gas emplacement in reservoirs include oil accumulation under the paleo-traps setting, succedent moderate alteration in structure, increasing maturation due to basin superposition, and faults as passageways of hydrocarbon migration. It is significant to seek for original and/or secondary oil-cracking gas from Cambrian source rocks in Caledonian-Hercynian. paleo-reservoirs.