渤海湾盆地黄骅坳陷潜山油气成藏差异性及主控因素

Differential hydrocarbon accumulation of buried hills and its main controlling factors in the Huanghua Sub-basin, Bohai Bay Basin

渤海湾盆地中、古生代经历了多期构造演化,导致潜山油气藏类型复杂多样,以黄骅坳陷为例,对渤海湾盆地潜山油气成藏差异性及主控因素进行研究,认为盆地构造演化、源储发育特征及其配置关系控制了不同类型潜山油气藏的形成及其成藏特征差异。综合考虑潜山形成机理、圈闭构造特征及源储配置关系,潜山油气藏可划分为断块-地貌型、断块-断鼻型、背斜型和断块-背斜型等4种类型,且以断块-断鼻型最为发育。研究结果表明:4种类型潜山油气藏在油气分布特征、油气来源、油气成藏期次及成藏模式等方面均存在明显差异,其中断块-地貌型油气藏普遍缺失石炭-二叠系,下古生界油气富集程度高,原油δ^(13)C_(饱和烃)小于-27‰、δ^(13)C_(芳烃)小于-27.5‰,天然气δ^(13)C_(2)大于-26.0‰、仅新近纪—第四纪发生一期充注,油气成藏特征表现为"源储侧接—古近系供烃—晚期成藏—供烃窗口富集";断块-断鼻型油气在中、古生界均有分布且混源特征明显,油气成藏特征表现为"源储分离—双源供烃—二期充注—多层系差异富集";背斜型古生界油气富集程度高,原油碳同位素大于-28‰、天然气δ^(13)C_(2)普遍大于-26.0‰,油气成藏特征表现为"源储叠置—煤系供烃—二期成藏—古生界富集";断块-背斜型则中生界和上古生界富油、下古生界富气,原油碳同位素小于-30‰、仅新近纪—第四纪发生一期充注,天然气δ^(13)C_(2)普遍大于-26.0‰、存在二期充注,油气成藏特征为"源储叠置—侧接复合—双源供烃—二期成藏—供烃窗口富集"。盆地构造演化的差异从根本上控制了潜山油气藏类型,进而导致烃源岩展布及源储配置关系的差异,多套烃源岩分布控制油气来源与分布差异,烃源岩热演化与生烃的多期次性控制油气成藏期次差异,源储配置控制了油气富集层系,储层发育差异则控制了油气富集程度.

The Mesozoic-Paleozoic in the Bohai Bay Basin underwent multi-stage tectonic evolution, resulting in the multiple types of buried-hill reservoirs. Taking the Huanghua Sub-basin as an example, this paper discussed the differential hydrocarbon accumulation and its major controlling factors. It can be concluded that the basin structural evolution, characteristics of source rocks and reservoirs development, and their configuration relationship control the formation of different types of buried-hill reservoirs and differences in hydrocarbon accumulation. The M-P buried-hill reservoirs can be divided into four types considering the buried-hill formation mechanism, trap characteristics, and source-reservoir relationship, i.e. the fault block-landform type, fault block-fault nose type(dominant), anticline type, and fault block-anticline type. The results showed that obvious differences occur in the four types of buried-hill reservoirs in hydrocarbon distribution, origin and source, accumulation periods and models. The fault block-landform reservoir is lack of C-P and mainly enriched oil and gas in the Lower Paleozoic. The δ;C of saturated hydrocarbon is lighter than-27‰ and that of aromatic hydrocarbon is lighter than-27.5‰ of crude oil, and δ;C;of natural gas is heavier than-26‰. Oil and gas only accumulated at N-Q, and the hydrocarbon accumulation characteristic is “source-reservoir lateral contact—Paleogene source—late period accumulation—rich in the hydrocarbon supply window”. While the fault block-nose reservoir is rich in oil and gas in Mesozoic to Paleozoic reservoirs with mixed source, and the hydrocarbon accumulation feature is “separated source-reservoir—double sources—two charging periods—rich in multi layers”. And the anticline reservoir is rich in hydrocarbons in Paleozoic, δ;C of crude oil is heavier than-28‰ and δ;C;of natural gas is heavier than-26‰. And the hydrocarbon accumulation feature is “source-reservoir superimposition—coaly source—two charging periods—rich in Paleozoic”. While the fault block-anticline reservoir is with oil rich in the Mesozoic and the Upper Paleozoic and gas rich in the Lower Paleozoic. The δ;C of crude oil is lighter than-30‰ with one charging period at N-Q while δ;C;of natural gas is heavier than-26‰ with two charging periods, and the hydrocarbon accumulation characteristic is “source-reservoir superimposition—lateral contact relationship—double sources—two charging periods—rich in the hydrocarbon supply window”. The differential tectonic evolution fundamentally controls the formation of different types of buried-hill, further leading to the differences in the distribution of source rocks and the relationship between source and reservoir. While the multiple sets of source rocks control the source and distribution difference of oil and gas, and the thermal evolution of source rocks and the multiphase of hydrocarbon generation control the difference of hydrocarbon accumulation stages. In addition, the source-reservoir configuration controls the hydrocarbon enrichment layers, while the pore throat characteristics of reservoir control the degree of hydrocarbon enrichment.