油藏演化的两个极端过程

Two possible fates for paleo-reservoir oils

油气藏形成之后,在地质条件变化不大的情况下,储集层中的油气一般保持相对的稳定。但当地质条件变化较大时,油气藏中则发生明显的蚀变。其中两个极端的演化过程,一是抬升破坏形成生物降解沥青,一是深埋发生原油裂解转化成焦沥青和天然气。生物降解沥青没有一定的形态,在显微镜下呈席状分布,沥青反射率低,抽提物具有明显的生物降解特征。原油裂解形成的焦沥青具有一定的几何形态,沥青反射率很高而无常规抽提物。原油裂解生成的天然气在组分和碳同位素特征上与干酪根裂解生成的天然气有别。

Oil in paleo-reservoirs may subject to two alternative fates when geological conditions change. Oil may be biodegraded into bitumen reservoirs are uplifted, or it can be transformed into pyro bitumen and gas due to cracking when it is deeply buried. The biodegraded bitumen does not possess specific morphology. It has low reflectivity and its extracts are of obvious biodegrading charcaters. The cracked pyrobitumen has several regular morphologies, with higher reflectivith but no extracts. The composition and carbon isotopic charcaters of gases generated from cracked oils are significantly different from those generated from cracked kerogen.