复合生烃系统——陆相断陷盆地烃源岩评价和油气预测的重要概念

COMPOSITE HYDROCARBON-GENERATION SYSTEM: AN IMPORTANT CONCEPT FOR SOURCE ROCK EVALUATION AND HYDROCARBON PREDICTION IN RIFT LACUSTRINE BASIN

复合生烃系统是指凹陷(或洼陷)具有两套或两套以上有机地球化学特征不同的有效烃源岩,它们具有多个成烃阶段和多期排烃运聚过程,形成了多种油气藏和多源油气藏。其特点可概括为“多套源岩、多阶段成烃、多源(混源)成藏的新模式”。渤海湾盆地油气勘探实践证明,丰富的油气资源及其分布特征与富含有机质生烃洼陷中存在的复合生烃系统具有十分密切的关系。渤海湾盆地复合生烃系统的组合特征可分为盐湖咸水湖相欠充填湖泊类型模式、半咸水微咸水深湖相平衡充填湖泊类型模式和淡水三角洲湖相过充填湖泊类型模式3种典型的湖相组合,其中所发育的烃源岩代表了复合生烃系统的基本特征。复合生烃系统发育在多幕式断陷活动的地质背景下,与不同油气储集性砂体相配合,通过不同的排烃方式和运移通道聚集成藏,形成了不同层系、不同区带和不同圈闭类型的复式油气聚集带,从而在空间上控制了盆地内各种油气藏的形成和分布。

Composite-Hydrocarbon Generation System (CHGS) meant two or more than two sets of effective source rocks with different organic geochemical characteristics in a depression, which underwent several stages of hydrocarbon generation, migration and accumulation, so as to form various pools with multiple sources. The exploration practice in the Bohai Bay Basin revealed that abundant oil and gas resources were closely related to CHGS in depression rich in organic matters. Three hydrocarbon generation models in the Bohai Bay Basin were summed up, namely, the model of saline water-underfilled salt water lake basin, the model of half saline water-fresh water balanced-fill deep lake basin, and the model of fresh water overfilled delta-lake basin, respectively. These source rocks represented three associations of CHGS. Under a geological background of multiple episodic fault-depressing activities, CHGS might combine with diverse sandy reservoirs and create composite hydrocarbon accumulation belts with different strata, sections and entraps by different expulsion manners and migration pathways. Consequently, CHGS controlled the formation and spatial distribution of various pools in petroliferous basins.