鄂尔多斯北部杭锦旗探区上古生界烃源岩评价

鄂尔多斯盆地北部杭锦旗探区上古生界烃源岩问题争议大。通过有机地球化学分析、盆地模拟等方法手段对研究区上古生界烃源岩展开研究。结果表明,上古生界发育石炭系、二叠系两套烃源岩,煤层是最好的烃源岩,泥岩为差烃源岩。煤层有机碳的质量分数最高,平均值为61.32%;有机质类型好,以Ⅲ型干酪根为主,属于生气型源岩;有机质成熟度为0.8%~1.3%,已经进入生气高峰阶段。烃源岩生气强度为(0.1~1.3)×109m3/km2,具备为研究区天然气成藏提供物质基础的条件。盆地模拟结果表明山西组总生气量大于太原组,是主要的烃源岩层系。烃源岩从侏罗纪末进入大规模生烃阶段,生烃高峰为早白垩世。研究区石炭系和二叠系煤层是上古生界天然气成藏的主要气源岩,天然气组分中甲烷含量变化、天然气侧向运移距离等证据进一步佐证了上述观点,突出了研究区上古生界烃源岩的原地性特征。

Evaluation of Upper Paleozoic source rocks of the Hangjinqi block in the northern Ordos Basin, China

The source rock problem on Upper Paleozoic of the Hangjinqi block of the northern Ordos Basin has been hotly disputed. The paper researches the Upper Paleozoic source rocks in the study area by the ways of organic geochemistry and basin model. Carboniferous and Permian formations are two sets of source rocks in the study area. Coalbeds are the best source rocks in the study area, while mudstone is a bad source rock. The coalbed is characterized by 61.32% organic carbon. Type Ⅲ kerogen is the main one with 0.8%～1.3% degree of organic metamorphism a gas-generating source rock and reaches the stage of gas-generating climax. The gas-generating intensity of this rock is (0.1～1.3)×10~9 m~3/km~2, and this source rock could satisfy the needs of gas accumulation. The total gas-generating content of Shanxi Formation is more than that of Taiyuan Formation, and the former is the main source rock of the study area. The source rock started to generate gas extensively from Late Jurassic, and the gas-generating climax was in Early Cretaceous. The research shows that the coalbed of Carboniferous and Permian is the main source rock of the Upper Paleozoic gas reservoir of the study area. The methane content variety of gas composition and the gas lateral migration distance further verifies the above conclusion and indicates the gas accumulation in place of Upper Paleozoic of the study area.