渤海海域渤中凹陷渤中19-6大型凝析气田天然气来源探讨

Gas source of BZ19-6 condensate gas field in Bozhong Sag, Bohai Sea area

仝志刚 李友川 何将启 姚爽

TONG Zhigang LI Youchuan HE Jiangqi YAO Shuang

中海油研究总院有限责任公司, 北京 100028 中海石油(中国)有限公司, 北京 100010

CNOOC Research Institute Ltd., Beijing 100028, China CNOOC China Ltd., Beijing 100010, China

渤海海域渤中19-6大型凝析气田的发现为渤中凹陷寻找大气田带来了希望和信心，深入研究其天然气的来源和成因对今后渤海天然气勘探具有重要指导意义。通过对开放和密闭体系热模拟实验结果分析，综合地球化学和数值模拟研究表明，渤海优质腐泥型湖相烃源岩[ω(TOC)=3.93%，IH=727 mg/g(每克有机碳中干酪根热解烃量，下同)]干酪根热解累积生气的比例仅为10%，以排油为主；偏腐殖型湖相烃源岩热解生气比例也不大，IH=100 mg/g时干酪根热解累积生气比例仅为30%，但由于干酪根的吸附作用，其中的残留烃在烃源岩中裂解成气，最后以排气为主。渤中19-6天然气为沙三段Ⅱ1、Ⅱ2和Ⅲ型混合烃源岩成熟到高成熟阶段的产物，是干酪根热解气与残留烃裂解气的混合物，且其供烃区为渤中凹陷西南的局部区域，供烃区古近系沙河街组沙三段烃源岩早期以排油为主，晚期(15 Ma以后)以排气为主，晚期排气量占总排气量的82%。下一步在渤中凹陷寻找大气田要选择供烃区烃源岩排烃气油比大、以排气为主的目标进行钻探。

The discovery of BZ19-6 condensate gas field in the Bozhong Sag of Bohai Sea area brought hope and confidence for giant gas fields. Intensive study of the source and genesis of natural gas in BZ19-6 gas field plays an important role for guiding natural gas exploration in the Bohai Sea. Open and sealed system pyrolysis as well as geochemical and numerical simulation show that the high-quality sapropelic lacustrine source rocks with an average TOC content of 3.93% and an IH index of 727 mg/g in the Bohai Sea area mainly generate oil, and only 10% of kerogens in the source rocks crack into gas. For humic-prone source rocks, about 30% of kerogens generate into gas when IH reaches 100 mg/g. However, the humic-prone source rocks still expel gas which is cracked from residual hydrocarbon due to the adsorption of kerogens. The natural gas in BZ19-6 gas field are mainly sourced from Ⅱ1, Ⅱ2 and Ⅲ type source rocks in the third member of Shahejie Formation during mature to high-maturity stages. They are mixtures of kerogen cracked gas and residual hydrocarbon cracking gas sourced from parts of the southwestern Bozhong Sag. The source rocks of the third member of Shahejie Formation in the hydrocarbon supply area mainly discharge oil in the early stage, and changed to gas after 15 Ma, accounting for 82% of the total gas discharge. To find large gas fields in the Bozhong Sag, the targets where source rocks have large gas/oil ratio and mainly expel gas should be focused on.

中海油重大科研项目“中海油'十三五’油气资源评价” YXKY-2018-KT-01

https://doi.org/10.11781/sysydz202202324