滇东北地区五峰-龙马溪组沉积转换及其页岩气地质意义

Sedimentary transformation of the Wufeng-Longmaxi Formation and its geologic significances of shale gas in Northeast Yunnan

关键词:  滇东北地区  云大页1井  五峰组  龙马溪组  沉积转换  页岩气地质

Key words:  Northeast Yunnan  Yundaye Well 1  the Wufeng Formation  the Longmaxi Formation  Sedimentary transformation  Shale gas geology

摘要:

上扬子地区五峰-龙马溪组富有机质页岩是当前海相页岩气勘探的主要层系，同时也是探索晚奥陶世生物大灭绝事件的重要窗口，是众多专家学者关注的焦点。但五峰期—龙马溪早期海平面变化和古气候演替的沉积响应是怎样的？这一重要的沉积学宏观描述及其沉积动力学分析尚末有相关报道。本文基于滇东北地区云大页1井的岩心描述，开展了五峰-龙马溪组沉积转换过程的沉积序列、沉积构造、矿物组分、有机碳同位素响应研究，并与邻井进行了对比分析，发现晚奥陶世至早志留世的古气候和古环境演替的沉积学响应是清楚的。自赫兰特阶寒冷事件和大规模海平面下降，至鲁丹阶深水陆棚相含碳质笔石页岩的转换过程是连续的，期间经历了三个相对短暂的阶段：浅水紊流、浅水层流到深水层流，其海侵过程是清楚的，地质记录是完整的。同时，研究认为，这一转换过程对五峰-龙马溪组富有机质页岩的物性及其含气性具有重要影响，是深入认识五峰-龙马溪组优质页岩各小层物性与含气性差异的重要基础。

Abstract:

The organic shale of the Wufeng-Longmaxi Formation in the upper Yangtze area is the main target sequences for marine shale gas exploration. It is also an important window to explore the event of the Late Ordovician mass extinction has been the focus of geological experts and scholars. The sedimentary response to the sea level changing and paleoclimate succession from the Wufeng to the Longmaxi period is still unclear, and the macroscopic description in sedimentology and its deposition kinetics analysis have not been reported. In this paper, based on the core description of the Yundaye well 1 in northeast Yunnan, the sedimentary sequences, sedimentary structures, mineral compositions, organic carbon isotope responses to the sedimentary transforming processes of the Wufeng-Longmaxi Formation were studied and compared with the adjacent wells. It was found that the sedimentary responses of the paleoclimate and paleo-environmental succession from the late Ordovician to early Silurian were clear. The conversion process from the Hirnantian cool event and large-scale sea level descent to the carbonaceous graptolite shale in the deep-water shelf facies of the Rhuddanian are continuous, during which three relatively transient stages, shallow water turbulence, shallow water laminar flow and deep water laminar flow, have been experienced. The transgression process is clear and the geological record is complete. At the same time, it is concluded that this transformation process has an important influence on the physical properties and gas-bearing properties of the organic-rich shale in the Wufeng-Longmaxi Formation, and it is an important basis for further understanding the differences between different layers of organic-rich shale in the Wufeng-Longmaxi formation.