徐家围子断陷深层烃源岩生烃条件研究

松辽盆地徐家围子断陷4套烃源岩中沙河子组暗色泥岩和煤层最为发育，其平均有机碳值分别为1.59%和32.8%，原始生烃潜力较大；有机质类型以Ⅲ型为主，少量为Ⅰ型和Ⅱ型，以生气为主；断陷边部烃源岩大都处于高成熟阶段，断陷中部沙河子组烃源岩R_o全部大于2.0%，处于过成熟阶段。徐家围子断陷从火石岭组沉积开始，大地热流值逐渐升高，白垩纪末期达到最大值2.3 HFU，然后地层逐渐冷却，大地热流值降至现今的1.75 HFU。徐深1井沙河子组暗色泥岩到现今的累积生气强度达到38×10⁸m³/km²，达到形成大气田的气源条件。距今90 Ma和80 Ma出现2次显著的生气高峰，对应泉头组沉积时期和姚家组沉积时期，区域盖层已经完全具有封闭能力，对天然气的后期保存比较有利。

A STUDY OF HYDROCARBON GENERATION CONDITIONS OF DEEP SOURCE ROCKS IN XUJIAWEIZI FAULT DEPRESSION OF THE SONGLIAO BASIN

Among the four source rock groups in Xujiaweizi fault depression in the Songliao Basin, the dark mudstone and coal bed in Shahezi Formation are the most developed, with average organic carbon values being 1.59% and 32.8% respectively, thus their initial hydrocarbon generating potentials are relatively large. The organic materials are dominated by type Ⅲ kerogen and some are of typeⅠ and Ⅱkerogens and they mainly generate gaseous hydrocarbons. Most of the source rocks on the edge of the fault depression are in high mature stage, while the source rocks in Shahezi Formation in the central part of the fault depression are in post mature stage with Ro value over 2.0%. In Xujiaweizi fault depression, the geothermal heat flow value began to progressively increase since the deposition of Huoshiling Formation and reached the maximum value of 2.3 HFU at the end of Cretaceous, and then decreased progressively to 1.75 HFU at present. The cumulative gas generation intensity of the dark mudstone in Shahezi Formation in the well Xushen 1 is 3.8 BCM/km2, indicating that the source rock meet the essential requirements for the formation of a large gas field. Two gas generation peaks occurred in 90Ma and 80Ma, which corresponded to the deposition of Quantou and Yaojia formations respectively. The regional seals had been fully developed at that time, thus were favorable for late preservation of gas.