彭水地区五峰—龙马溪组页岩热演化史及生烃史研究——以PY1井为例

利用盆地模拟软件Basin Mod 1-D,选用古地温梯度法,采用镜质体反射率正演法厘定彭水地区各时期构造剥蚀量及古地温梯度。结果表明,该区自晚古生代以来古热流经历了低—高—低的变化过程,其古地温梯度具有相同特征;志留纪—中二叠世古地温梯度平均值约为2.5~3.0℃/hm;晚二叠—早白垩世古地温梯度平均值约为3.0~3.5℃/hm;早白垩世末期以来,古地温梯度平均值介于2.0~2.5℃/hm;加里东期、印支期构造抬升剥蚀量不足500 m,燕山、喜马拉雅运动构造抬升剥蚀量可达4 300 m。成烃史研究表明,彭水地区五峰—龙马溪组页岩早泥盆世进入生油门限,在晚二叠—晚三叠世进入生油高峰,在早侏罗世进入生气期,中侏罗世进入过成熟生干气阶段。后期燕山、喜马拉雅运动,致使地层抬升、剥蚀,研究区页岩气保存条件将成为下一步勘探的研究重点。

Thermal and hydrocarbon generation history of Wufeng and Longmaxi shales in Pengshui area,eastern Sichuan Basin:A well PY1 case study

The erosion thickness and paleogeothermal gradient of the Pengshui area in the eastern Sichuan Basin during various tectonic movements were established by means of vitrinite reflectance forward modeling and basin modeling software (BasinMod 1-D). Since the Late Paleozoic, the paleo heat flow and paleogeothermal gradient in the study area first increased and then decreased. The average paleogeothermal gradients from Silurian to the Middle Permian, from the Middle Permian to the Early Cretaceous, and from the end of the Early Cretaceous until now were 25–30 °C/km, 30–35 °C/km, and 20–25 °C/km, respectively. In the Caledonian and Indosinian periods, the erosion thickness of the study area was less than 500 m; while in the Yanshanian and Himalayan periods, it reached 4 300 m. The Wufeng and Longmaxi shales entered the threshold of oil generation in the Early Devonian, and reached peak generation from the Late Permian to the Late Triassic. Gas generation started in the Early Jurassic, and over-mature dry gas was generated in the Middle Jurassic. In the following Yanshan and Himalayan movements, the study area was uplifted and eroded, which raised challenges for the preservation of shale gas.