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东方区与乐东区是莺歌海盆地2个主要天然气探区,2个区中新统烃源岩有机质成熟度存在较大差异,表现为相同埋深时东方区有机质演化程度比乐东区高。在莺歌海盆地构造演化、温压场与烃源岩地球化学特征研究的基础上,通过沉积过程分析与盆地模拟相结合探讨有机质热演化差异的成因。研究认为:新近纪至第四纪盆地沉积沉降中心由东方区向乐东区迁移,导致二者在不同时期的沉积速率不同。尽管盆地的高温高压场对有机质热演化产生一定影响,但造成东方区与乐东区有机质热演化差异的主要原因是2个区不同的沉积速率。而有机质热演化差异造成了生气过程的差别:东方区生气时间早、持续时间长,而乐东区表现为晚期快速生气的特点,更有利于天然气的聚集成藏。乐东区中新统烃源岩生烃过程中有机酸的形成时间也较晚,有助于该储层次生孔隙的发育,因此乐东区成藏条件更优越,勘探前景良好。该成果不仅对莺歌海盆地天然气勘探具有重要的指导作用,同时对其他区域也具有较为广泛的借鉴作用。
Dongfang and Ledong are two major natural gas exploration areas in Yinggehai Basin. There are large differences in organic matter maturity of Miocene source rocks in the two areas, showing that the organic matter evolution in the eastern area is higher than that in Ledong area at the same depth. Based on the study of tectonic evolution, temperature and pressure field and geochemical characteristics of source rocks in Yinggehai Basin, the causes of differences in thermal evolution of organic matter are discussed through the combination of sedimentary process analysis and basin modeling. The study suggests that the depositional sedimentation center of Neogene to Quaternary sediments migrated from Dongfang to Ledong, resulting in different sedimentation rates at different periods. Although the high-temperature and high-pressure fields in the basin have an impact on the thermal evolution of organic matter, the main reason for the differences in the thermal evolution of organic matter in the eastern and eastern Ludong areas is the different sedimentation rates in the two regions. The differences in the evolution of organic matter caused the difference in the process of anger: the gas generation in the eastern region was earlier and longer in duration, whereas the performance in the eastern region was characterized by rapid gas evolution in the late stage, which was more conducive to the accumulation and accumulation of natural gas. During the hydrocarbon generation process of the Miocene source rocks in the Ledong area, the formation time of organic acids is also later, which is conducive to the development of secondary pores in the reservoir. Therefore, the reservoir formation conditions in Ludong area are superior and exploration prospect is good. This result not only plays an important guiding role in natural gas exploration in Yinggehai Basin, but also has a wider reference for other regions.