昭通示范区页岩气富集高产的地质主控因素

昭通页岩气示范区具有"强改造、过成熟、杂应力"特征,页岩气富集高产控制因素复杂。为实现页岩气规模高效勘探开发,应用昭通页岩气示范区实际勘探开发资料,系统总结了昭通页岩气田富集高产的地质主控因素,认为：①海侵体系域富碳高硅页岩为页岩气的富集提供物质基础。海侵体系域的贫氧-厌氧的深水环境,沉积速率慢,硅质生物繁盛,有利于富有机质页岩的形成与保存。海侵体系域（五峰组-龙马溪组一段1亚段3小层）富碳高硅页岩,有机质孔和微裂缝发育,吸附能力和含气性强,且可压性好。②适当的后期构造改造与高压封存箱的有效保存是富集高产的关键。昭通示范区北部中生界复向斜位列构造转换带,改造强度适中,3组方向最大主应力汇聚的复向斜槽部,网状缝发育,具有多元汇聚成藏优势。前期良好的顶底板封盖所形成的高压封存箱,在晚期适度抬升中得以有效保存。以昭通示范区页岩气富集主控因素为指导,优选龙马溪组一段1亚段1小层-2小层为甜点层段,其北部的黄金坝、紫金坝、云山坝及大寨区块为页岩气富集区,后期构造改造强度不同则导致了不同构造部位甜点区页岩气富集高产的差异性。

Main geological controlling factors of shale gas enrichment and high yield in Zhaotong demonstration area

Zhaotong shale gas demonstration area is characterized by "strong transformation, over-maturity and complex stress", where the control factors of shale gas accumulation and high yield are complicated. To achieve the large-scale highly-efficient shale gas exploration and development, based on the previous understanding of southern marine shale gas enrichment law, the actual exploration and development data of Zhaotong shale gas demonstration area are used to systematically summarize the main geological controlling factors for the enrichment and high yield of Zhaotong shale gas field. It is considered that (1)the carbon-rich high-silicon shale in transgressive system tract provides a material basis for shale gas enrichment. The oxygen-poor and anaerobic environment in transgressive system tract is characterized by slow deposition rate and rich siliceous life, which is conducive to the formation and preservation of organic-rich shale. For the carbon and silicon-rich shale (Wufeng Formation-Sublayer 3, Sub-member 1, Member 1 of Longmaxi Formation)in the transgressive system tract, organic pores and micro-fissures are developed with strong adsorption capacity and gas-bearing capacity as well as favorable compressibility. (2)The key to gas enrichment and high yield is the proper post-structural transformation and the effective preservation of high-pressure sealed box. The Mesozoic synclinorium in the northern Zhaotong demonstration zone is located in the tectonic transformation belt with moderate reform intensity. The maximum principal stresses in three directions are converged to the synclinorium groove with the development of mesh fissures and the advantage of hybrid accumulation mode. In the early stage, the high-pressure sealed box is formed under good roof and bottom sealing conditions, which is preserved effectively in the later moderate uplift. In Zhaotong demonstration zone, the dual-controlling factors of gas enrichment are taken as the guidance to optimize the Sublayers 1-2, Sub-member 1, Longmaxi Formation as sweet spot horizons, of which the north Huangjinba, Zijinba, Yunshanba and Dazhai blocks are shale-gas enrichment regions. The tectonic transformation intensities are different in late period, leading to the difference in the shale gas enrichment and high yield of sweet spot areas at different tectonic locations.