伦坡拉盆地热演化史及有利区带预测

Thermal evolution history and prediction of favorable zones in Lunpola Basin

伦坡拉盆地是西藏地区已发现的最具油气勘探潜力的盆地,勘探前景广阔。为研究该区烃源岩热演化史和油气运聚规律,开展了钻井岩心分析、二维地震资料解释、单井热演化史模拟、油气运聚模拟及分析等研究工作。结果表明:①在W1和W2井牛堡组三段下亚段底部识别出厚层的浊积砂体;②始新世末期,受高热流和高地温梯度双重作用的影响,牛堡组二段中亚段烃源岩开始生烃,并一直持续至今,烃源岩的成熟呈现出西早东晚的趋势,期间油气主要在蒋日阿错凹陷和江加错凹陷发生少量运移,并在凹陷内部的隆起带及周缘聚集;③渐新世早期,爬错凹陷发生大规模运移,油气沿优势运移通道向北和向南,并通过断层向上覆地层运移。由此推测,在盆地北部的逆冲推覆带中段和南部冲断隆起带中西段,以及江加错凹陷的东部和爬错凹陷的西部存在10处有利油气聚集带。该研究成果为伦坡拉盆地的油气勘探提供了依据。

Lunpola Basin is the most oil-gas exploration potential basin found in Tibet,and has a broad prospect for exploration. In order to study the thermal evolution history of source rocks and the law of oil and gas migration and accumulation in this area,drilling core analysis,2-D seismic data interpretation,single well thermal evolution history modeling,simulation analysis of oil-gas migration and accumulation were carried out. The results show that:(1)Thick turbidite sand bodies were identified at the bottom of the lower submember of the third member of Niubao Formation in wells W1 and W2.(2)At the end of Eocene,affected by the double action of high heat flow and high geothermal gradient,the source rocks of the middle submember of the second member of the Niubao Formation began to generate hydrocarbons and the process has been continuing to this day. The maturation of source rocks tended to be early in the west and late in the east. During this period,a small amount of hydrocarbon mainly migrated in Jiangri Aco Sag and Jiangjiaco Sag,and accumulated in the uplift zone and its periphery in the sag.(3)In the early Oligocene,large-scale hydrocarbon migration took place in Pacuo Sag. Hydrocarbon migrated northward and southward along the dominant migration pathway and upward through faults. It is inferred that there are 10 favorable oil-gas accumulation zones in the middle part of the thrust nappe belt in the northern basin and in the middle and western part of the southern thrust uplift belt in the southern basin,as well as in the eastern part of Jiangjiacuo Sag and the western part of Pacuo Sag. The study results provide a basis for oil and gas exploration in Lunpola Basin.