断层流体锶、碳、氧同位素示踪评价断层垂向封闭性--以焦石坝背斜带为例

锶同位素不易分馏、年代可对比的特性决定其能够作为有效的断层流体示踪指标。氧同位素能反映温度、流体等因素，碳同位素能反映有机质的影响，是锶同位素的有力补充。利用流体示踪图可以判断断层不同部位开启的期次与可能联通范围。针对四川盆地焦石坝背斜带周缘的断层，利用脉体锶、碳、氧同位素开展断层垂向封闭性评价。评价结果表明:焦石坝地区志留系以下地层联通，存在一期深部壳源富锶流体，志留系下部的流体未通过断层向上运移。该地区后期至少经过两期构造运动，针对志留系龙马溪组页岩气，焦石坝背斜带周边不同断层的垂向封闭性具有明显差异。从平面上看，方斗山断裂带中部、大耳山断裂带南部、乌江断裂带南部断层垂向封闭性差；大耳山断裂带北部、乌江断裂带北部、天台场断裂带南部断层垂向封闭性中等；方斗山断裂带北部、南部、天台场断裂带北部垂向封闭性好。

Evaluation of Vertical Sealing of Faults by Strontium,Carbon and Oxygen Isotope Tracing of Fault Fluid: A case from the anticlinal belt in Jiaoshiba area

Because the strontium isotope is not easy to be fractionated and can be compared with the time, the stronti-um isotope can be used as an effective index of fluid tracing. Oxygen isotopes can reflect the temperature, fluid and other factors, and carbon isotopes can reflect the organic matter, so they can be used as the strontium isotope supple-ment. The time and possibility of opening of in different parts of the fault can be judged by using fluid tracing diagram. In this paper, we take the example of faults around the anticlinal belt Jiao Shi Ba and make use of strontium, carbon and oxygen isotopes in the veins to study the vertical sealing of faults. The evaluation results show that the strata under the Silurian strata are communication in this area and there is a period of strontium-rich fluid from deep crust. But pro-tected by decollement from mudstone in the Silurian strata, the period of strontium rich fluid cannot migration to upper strata through faults. This area was at last through two times of tectonic movement in the late period. Aiming at Silurian Longmaxi shale gas reservoir, different faults have obvious differences. From the plane of view, the vertical sealing of faults in the middle of Fangdoushan fault zone, and the south of Daershan fault zone, the south of Wujiang fault zone is bad. The vertical sealing of faults in the north of Wujinag fault zone, the south of Tiantaichang fault zone is medium. The vertical sealing of faults in the north of Fangdoushan fault zone, the south of Fangdoushan fault zone, and the north of Tiantaichang fault zone is good.