松辽盆地南部长岭断陷CO2成因与成藏期研究

Genesis and Accumulation Period of the CO_2 in Changling Fault Depression of Songliao Basin,Northeastern China

长岭断陷是松辽盆地最主要高含油气区域,目前发现的天然气控制储量超过2 000亿m3。从长岭断陷高含天然气的地球化学特征入手,通过对储层包裹体中气体的组成和碳同位素的分析,并结合区域地质和构造历史的研究指出:长岭断陷的CO2为无机幔源成因,目前已知的CO2气藏成藏时间是在新生代晚期,而不可能是营城组火山岩在后期缓慢脱气形成;储层中不发育包裹体的原因有2个,一是CO2的充注速度快,包裹体来不及生长,二是在CO2充注以前,储层已经被烃类气体所饱和,缺水的储层地质环境,不适宜包裹体的形成。

Changling fault depression is one of the gas-rich areas in the Songliao basin, north-eastern China. The probable reserve of natural gas is up to 2 ×108 m^3. Geochemical analyses of the gas compositions in the inclusions and the carbon isotope and the study on regional geology and structural history reveal that the CO2 in this area is mantle-derived origin and could not be from the degassification of volcanic rocks in Yingcheng formation. The accumulation period of CO2 is in later Cenozoic. There is no CO2 inclusions grown in reservoir rocks for two reasons. Firstly, the inclusions could not be enclosed by authigenic mineral for fast jnjection of CO2 which related with volcanic event. Secondly, the CO2 inclusion could not be formed without water in the pore space of reservoir, for the space had been full of hydrocarbon gases when CO2 injected.