四川盆地东南缘志留系古油藏特征及其油气勘探意义

Characteristics of Silurian Paleo-oil reservoirs and their significance for petroleum exploration on the southeast margin of Sichuan Basin

为明确四川盆地周缘志留系碳酸盐岩油气成藏特征,通过地表地质和地下地质相结合,应用岩相学和有机地球化学手段,对四川盆地东南缘下志留统石牛栏组礁滩相沉积特征和古油藏进行了精确刻画和深入解剖,认识到石牛栏组由3个向上变浅的沉积旋回构成,其中第三个旋回在林滩场-良村-丁山构造一带发育有台地边缘生物礁滩相沉积,礁滩相储层内部沥青发育,为礁滩型岩性古油藏,但古油藏分布较零星、规模较小,恢复古油藏量约为6.62×103t。古油藏的油源主要来自于震旦系古油藏原油逸散跨层充注,但可能存在志留系烃源岩的生烃充注。古油藏的形成和破坏过程如下:震旦系古油藏遭受破坏,原油充注到石牛栏组,形成古油藏(晚三叠世—早侏罗世)—持续深埋,原油裂解,形成古气藏(中侏罗世—中白垩世)—褶皱及快速隆升作用,古气藏遭受破坏(80 Ma至现今)。川东南地区志留系油气勘探前景不容乐观,而川东-渝东地区将是志留系最为有利的勘探地区。

In order to understand the hydrocarbon accumulation characteristics of the Silurian carbonates on the southeast margin of Sichuan Basin, this paper studied reef-shoal facies sedimentary features and paleo-oil reservoirs in the Lower Silurian Shiniulan Formation based on the comprehensive field and laboratory research of petrography and geochemical analysis. The Lower Silurian Shiniulan Formation is composed of upward-shallowing three cyclic deposits ,of which the third cyclic deposits are bioherm-shoal facies on platform margin occurring along Lintan- chang-Liangcun-Dingshan structures. The reservoirs of reef-shoal facies are rich in bitumen, indicating that they are lithologic paleo-oil reservoirs of shoal-reef type. These paleo-oil reservoirs are small in resource scale and scat- ter in regional distribution. Their resources are estimated to be about 6. 62×10^3 t. The oil of the paleo-oil reservoir is mainly sourced from the Sinian paleo-oil reservoir,partly from the Silurian source rocks. The formation and de- struction of the Shiniulan paleo-oil reservoir includes the following process：the Sinian oil reservoirs were destroyed and the escaping oil accumulated in the Shiniulan Formation to form the oil reservoir（ Late Triassic to Early Juras- sic）. The oil of the oil reservoir was cracked to gas due to the long term deep burial, to lead to the gas reservoir （Middle Jurassic to Middle Cretaceous）. Finally, the gas reservoir was destroyed by folding and quick uplifting （ since 80 Ma）. The exploration prospect in the Silurian in southeast Sichuan Basin is not as good as in the eastern Sichuan-eastern Chongqing.