银额盆地拐子湖凹陷北部地区白垩系烃源岩特征

Characteristics of Cretaceous source rocks in northern Guaizihu Sag,Yingen-Ejinaqi Basin

为研究银额盆地拐子湖凹陷北部地区烃源岩特征,评价其生烃潜力,开展了探井全井段泥岩的地球化学测试,以探讨北部与中部烃源岩差异性成因,评价研究区油气成藏的油源条件。结果表明:①拐子湖凹陷北部潜在烃源岩主要发育于白垩系苏红图组、巴音戈壁组三段和巴音戈壁组二段,泥岩的有机质丰度普遍较低,但局部井段存在“甜点”,有机质类型以Ⅲ型为主,烃源岩达到成熟—过成熟热演化阶段。②相比于中部,北部源岩条件明显变差,可能受控于边界断层活动和凹陷结构的差异性引起的烃源岩在形成环境与母源输入方面的差异。③研究区有效烃源岩下限为w(TOC)大于1.35%,区内W1井—W2井区有效烃源岩面积较大,厚度大于20 m的烃源岩面积约133 km2,W2井含气层和储层沥青的发现表明研究区烃源岩具有一定的生烃潜力,且有过油气成藏史。该研究成果可为拐子湖凹陷下一步勘探决策提供依据。

In order to study the characteristics of source rocks and evaluate their hydrocarbon generating potential in northern Guaizihu Sag,geochemical tests of mudstone in the whole section of exploration wells were carried out to explore the differential genesis of source rocks in the northern and central parts,and oil source conditions for hydrocarbon accumulation in the study area were evaluated.The results show that:(1)the potential source rocks in the study area are mainly developed in Cretaceous Suhongtu Formation,the third and second members of Bayingebi Formation.The abundance of organic matter in mudstone is generally low,but there are“sweet spots”in some well sections.The type of organic matter is mainly typeⅢ,and the source rocks have reached mature to over-mature thermal evolution stage.(2)Compared with the central part of Guaizihu Sag,the condi‐tions of source rocks in the northern part are obviously worse,which may be controlled by the differences in the formation environment and source input caused by the differences in boundary fault activity and sag structure.(3)The lower limit of TOC content of effective source rocks in the study area is greater than 1.35%.The effec‐tive source rock area in well area W1-W2 is relatively large,and the area of source rocks with thickness greater than 20 m is about 133 km2.The discovery of gas-bearing layer and reservoir bitumen in well W2 shows that the source rocks in the study area have certain hydrocarbon generation potential and has a history of hydrocarbon ac‐cumulation.The research results can provide a basis for the next exploration decision-making in Guaizihu Sag.