四川盆地东部中二叠统茅口组孤峰段展布特征及其油气地质意义

Distribution characteristics of Gufeng Member of the Middle Permian Maokou Formation， eastern Sichuan Basin and its petrogeological significance

刘昇 范存辉 张本健 张亚 王尉 罗冰 白晓亮

Sheng LIU Cunhui FAN Benjian ZHANG Ya ZHANG Bing LUO Xiaoliang BAI

基于钻井岩-电特征和野外露头特征，结合区域沉积-构造格局，利用宏观及微观观察、主微量及稀土元素测试、总有机碳含量和镜质体反射率测定等手段对四川盆地东部中二叠统茅口组孤峰段展布特征、沉积环境和成藏条件进行研究。结果表明：①川东地区茅口组孤峰段的存在，证实茅口中、晚期受构造-沉积分异的影响，出现槽台格局。在茅口组二段B亚段沉积期（茅二B沉积期），川东地区孤峰段主要分布在盆地东北角。在茅口组二段A亚段沉积期（茅二A沉积期），孤峰段向南扩大到渠县—大竹—梁平，呈北西-南东向带状展布，厚度在0.8 ~ 26.6 m，川西北-川北则对应茅口组三段（茅三段）或茅口组四段（茅四段）。②孤峰段硅质页岩富含硅质放射虫，有机质含量高，具有典型的深水海槽相沉积特征。地球化学测试数据反映硅质页岩为深水缺氧还原环境且盐度较高，硅质来源以生物硅为主。③孤峰段烃源岩为一套富有机质的优质烃源岩，总有机碳含量整体较高、变化范围大，分布在1.69 % ~ 38.27 %，平均值为11.51 %，处于成熟-过成熟阶段。④川东地区孤峰段优质烃源岩可通过断裂与开江-梁平海槽礁滩相储层沟通，构成“下生上储”的源-储关系；此外，也可与茅口组优势滩相储层形成“旁生侧储”的成藏组合。川东地区孤峰段有望作为区域内优质烃源岩的接力勘探层系，对研究区内下一步油气勘探开发具有重要意义。

The distribution characteristics， sedimentary setting and reservoir formation conditions of the Gufeng Member of the Middle Permian Maokou Formation in the eastern Sichuan Basin were studied by means of macroscopic and microscopic observation， as well as the measurement of major and minor elements and rare earth elements （REEs）， total organic carbon （） content and vitrine reflectance， while considering the lithologic and electrical properties and outcrop characteristics， combined with regional depositional-tectonic framework. The results are as follows. First， the existence of Gufeng Member of the Maokou Formation in eastern Sichuan Basin confirms that a trough and platform pattern existed in the middle and late depositional stages of the Maokou Formation under the tectonic-sedimentary differentiation. During the deposition of the B sub-member of the second member of the Maokou Formation （i.e.， the deposition of Mao 2B sub-member）， the Gufeng Member mainly occurred in the northeast corner of the eastern Sichuan Basin. During the deposition of Mao 2A sub-member， the Gufeng Member extended southward to Quxian， Dazhu， and Liangping counties in a NW-SE-striking strip pattern with a thickness of 0.8 to 26.6 m. The Gufeng Member corresponds to the Mao 3 and 4 members in northwest and north Sichuan Basin. Second， the siliceous shale in Gufeng Member is rich in siliceous radiolaria and has high organic matter content， which is typical of deep-water trough facies deposition. The geochemical test data show that the siliceous shale is developed in a deep-water anoxic reducing environment with high salinity， with biogenic silica as the main siliceous source. Third， the source rocks in the Gufeng Member are of high quality and rich in organic matter， with the total organic carbon （） content being relatively high as a whole but in a wide variety， ranging from 1.69 % to 38.27 %， with an average value of 11.51 %， and in the mature to over-mature stage. Fourth， the high-quality source rocks of the Gufeng Member can communicate with the reef-shoal reservoir of Kaijiang-Liangping trough through faults， forming an “upper source rock-lower reservoir” assemblage； and it can also form a juxtaposed “source rock- reservoir” association with the favorable beach reservoir of Maokou Formation. The Gufeng Member in eastern Sichuan is expected to be a successor target for high-quality source rock exploration in the region， which is of great significance to future oil/gas exploration and development in the study area.

10.11743/ogg20230415