柴达木盆地狮子沟油田古近系油气成藏期次

Analysis of hydrocarbon accumulation period in Paleogene reservoirs, Shizigou oilfield of Qaidam basin

柴达木盆地狮子沟油田古近系蕴藏着丰富的油气资源,但多年来其深层油气勘探一直未取得突破,油气成藏期次的不明确阻碍了对其油气成藏过程的准确认识。通过对狮子沟油田古近系储层流体包裹体的镜下观察、荧光分析以及均一温度和盐度测试,对其古近系油气成藏期次进行研究表明,研究区古近系主要发生2期油气充注事件。结合埋藏史和热演化史分析可知,第1期油气充注发生于上新世中期,距今约12～10Ma,捕获的流体包裹体以浅黄色、黄绿色液态烃和气液烃为主;第2期油气充注发生于上新世末期,距今约4～2Ma,捕获的流体包裹体以黄绿色和绿色气液烃为主。此外,研究区油气藏还具有多期充注和持续充注的特征,但主要的油气充注时期均相对较晚,晚期形成的油气藏规模更大。

It is proved by practice of exploration that the Shizigou Paleogene reservoir contains abundant hydrocarbon resources, but deep oil-gas exploration didn't make a big breakthrough, and the major reason is that, a poor understanding of hydrocarbon accumulation stages restrains the accurate research about accumulation process. In this paper, through the microscopic observation, fluorescence analysis and homogenization temperature and salinity test of fluid inclusions in Paleogene reservoirs of study area, the hydrocarbon charging history of Paleogene reservoir have been discussed. The result shows that there are two major stages. By integrating with the study on the burial and thermal history, the first change occurs in middle Pliocene(12-10 Ma bp) and the entrapped fluid inclusions are mainly consisted of liquid hydrocarbon and gas-liquid hydrocarbon with buff-yellow and yellow-green fluorescent light. The second time occurs in the final stage of Pliocene (4-2 Ma bp) and the entrapped fluid inclusions are mainly consisted of gas-liquid hydrocarbon with yellow-green and green fluorescent light. In addition, the reservoirs in study area also have the characteristics of multi-stage charging and continual charging, but major fluid injection time is in the later period on the whole. Therefore, the scale of later hydrocarbon accumulation is larger.