海拉尔盆地呼和湖凹陷南屯组油气成藏期次研究

Study on hydrocarbon accumulation stages in Nantun formation, Huhehu depression, Halaer Basin

海拉尔盆地呼和湖凹陷南屯组是该区近期新增规模储量的潜力地区,但南屯组油气成藏期次不明确阻碍了对油气成藏过程的准确认识。为此采用生烃史和流体包裹体综合分析的方法,同时结合单井沉积史与热史分析,对研究区南屯组生油岩生烃和储层注烃2个油气成藏过程展开分析,厘定了南屯组油气成藏期次。应用化学动力学方法评价生烃史的结果表明,研究区主力烃源岩南屯组的生烃期为125～115Ma,对应的地质时期是伊敏组沉积中晚期;南屯组烃源岩生油高峰对应的依敏组沉积中晚期就是油气的主要成藏期。应用流体包裹体法分析得到的油气主要充注期为118～112Ma,略晚于生烃期。考虑到排烃期、运聚期要略滞后于生烃期,2种方法分析结果相互佐证,由此认为依敏组沉积中晚期是呼和湖凹陷南屯组油气大量充注的主要成藏期。

The Nantun formation in Huhehu depression of Halaer Basin is the most promising for reserve growth in the area. However, a poor understanding of the hydrocarbon accumulation stages in the formation restrains further probe into the accumulation processes, and making it difficult to obtain a breakthrough in exploration. To solve the problem, we employed a comprehensive analysis method that combines the study of hydrocarbon generation history and fluid inclusion with analysis of sedimentary and thermal history of single wells. By analyzing hydrocarbon generation of the source rocks and hydrocarbon charging of the reservoirs, we identified its accumulation stages. An evaluation of hydrocarbon generation history with chemical kinetic method shows that the major source rocks generated hydrocarbon during 115-125Ma, corresponding to the mid and late period of the Yimin formation. It is supposed that the period between intensive hydrocarbon generation and charging is short, then, the mid and late period of the Yimin formation, when the peak oil generation of the Nantun formation occurred, could be the main hydrocarbon accumulation stage. An analysis of fluid inclusion indicates a major charging period of 112-118Ma, a little later than the hydrocarbon generation stage. Considering that the hydrocarbon expulsion and migration slightly postdate hydrocarbon generation, the results from these two analysis methods correspond to each other. Therefore, we conclude that the mid and late period of the Yimin formation is the major hydrocarbon accumulation stage.