塔里木盆地石炭系烃源岩成熟演化研究

Maturity evolution of the Carboniferous source rocks(CSR)in the Tarim Basin,Northwest China

尽管塔里木盆地石炭系富含有机质且已发现其生成的原油,但关于石炭系烃源岩热演化研究却很薄弱.根据基础地质资料、古地温梯度和实测镜质体反射率数据,本文定量模拟了塔里木盆地6口典型井的石炭系烃源岩热演化史和这套烃源岩底界、顶界在二叠纪末期、三叠纪末期、白垩纪末期及现今成熟度的平面分布规律.塔北隆起南部、塔西南坳陷和阿瓦提凹陷在石炭—二叠纪作为沉降中心接受了巨厚的沉积物,造成这些地区石炭系烃源岩底界成熟度在二叠纪末期达到0.9％ ～ 1.3％（中—高成熟）,顶界为0.5％ ～0.9％（低—中成熟）,成为有利生油区.中生代时期,塔里木盆地中、东部长期处于沉降状态,石炭系烃源岩处于成熟演化阶段.白垩纪末期,塔中低凸起和满加尔凹陷的石炭系底界成熟度为0.7％ ～0.9％（中成熟）,顶界为0.5％～0.7％（低成熟）;而塘古孜巴斯坳陷底界成熟度为0.9％ ～1.1％（中—高成熟）,顶界为0.7％ ～0.9％（中成熟）.受羌塘地体、拉萨地体、印度板块分别与欧亚板块南缘碰撞远程效应的影响,塔西南坳陷和巴楚隆起在中生代一直处于隆升剥蚀状态,烃源岩热演化进入停滞状态.新生代以来,塔西南坳陷和阿瓦提凹陷演化为前陆盆地,再次接受了巨厚沉积物,致使石炭系烃源岩快速成熟演化,底—顶界成熟度现今已超过2.0％,进入干气阶段.满加尔凹陷石炭系烃源岩自石炭纪至今一直处于成熟演化阶段,现今达到最大,为0.8％ ～ 1.0％.另外,热史研究表明塔西南坳陷和阿瓦提凹陷石炭系烃源岩具有二次生烃潜力.本研究不仅丰富了塔里木盆地石炭系烃源岩热史研究成果,而且对油气勘探与开发具有重要的指导意义.

For the Carboniferous of the Tarim Basin, although it is rich in source rocks and the crude oil which generated were found, the studies on its thermal evolution are very few. Based on the geological data, paleo-geothermal gradient and measured vitrinite reflectance data, we simulated the thermal evolution of the Carboniferous source rocks（CSR） of 6 typical wells in the Tarim Basin and rebuilt quantitatively the maturity distribution characteristic of the base and top of the CSR in the end of Permian, the end of Triassic, the end of Cretaceous and present- day, respectively. As the deposition centers, the massive sediments were deposited in the southern Tabei uplift, Southwest depression and Awati depression during the Carboniferous and the Permian, which caused the maturity evolution of the CSR in these areas. In the end of Permian, the maturity of the base of the CSR in the southern Tabei uplift, Southwest depression and Awati depression reached to 0.9% - 1.3% （middle-high maturity） and the top was just 0.5% ~0.9% （low-middle maturity） , which indicated that these areas were favorable to generate oil in the Permian. The CSR in the central-eastern Tarim Basin always stayed in the maturity evolution stage due to the long-term deposition in the Mesozoic. The maturity of the base of the CSR in the Tazhong low-uplift and Manjiaer depression was 0.7% - 0.9% （middle maturity） and their top was 0.5%- 0.7% （low maturity） in the end of Cretaceous, while the base of the Tangguzibasi depression was 0.9% ~ I. I% （middle-high maturity）and its top was 0.7% ~ 0.9% （middle maturity）. The Southwest depression and Bachu uplift experienced uplift and erosion during the Mesozoic and the maturity of their SCR stopped evolution due to the distant effect from the collision among the Qiangtang block, Lhasa block and Indian plate with the southern margin of the Eurasia continent. Since the Cenozoic, the Southwest depression and Awati depression developed as the foreland basins and received massive sediments again, which caused the rapid evolution of the maturity of the SCR. The maturity of the base and top of the SCR in the Southwest depression and Awati depression is larger than 2.0% now and stays in the dry-gas stage. The maturity of the SCR in the Manjiaer depression always stayed in evolving since the Carboniferous and reach to the maximum with 0.8%- 1.0% now. In addition, the potential area of secondary hydrocarbon generation for the SCR were the Southwest depression and Awati depression. This study not only enriches the research on the thermal histories of the SCR, but also provides guidance for the oil and gas exploration and exploitation in the Tarim Basin.