古隆起边缘页岩气富集规律与选区——以雪峰西南缘下寒武统牛蹄塘组为例

Enrichment laws and regional selection of shale gas at the edge of palaeohigh: A case study on the Lower Cambrian Niutitang Formation on the southwestern margin of Xuefeng Uplift

关键词:  页岩气  雪峰古隆起  牛蹄塘组  富集规律  有利区

Key words:  shale gas  Xuefeng uplift  Niutitang Formation  enrichment laws  favorable exploration zones

摘要:

为进一步明确古隆起边缘页岩气富集主控因素，有效指导相似地质条件地区的页岩气选区评价，以雪峰西南缘下寒武统牛蹄塘组为例，结合最新勘探资料和前期认识，通过沉积相、演化历史和保存条件等综合研究，探讨了该区页岩气富集规律。结果表明：（1）牛蹄塘组下段页岩沉积于深水陆棚相，在热液活动参与下，发育高丰度、I型、富热成因硅的优质页岩，脆性矿物含量高，具有页岩气富集的基础；（2）热演化程度虽处于过成熟阶段，但有机质尚未碳化，生烃演化与储层演化相匹配，具备页岩气富集的前提；（3）燕山期以来的构造改造作用是否破坏了早期的保存条件，是页岩气富集的关键。基于上述富集规律认识，建立了雪峰西南缘页岩气选区评价标准，并指出在岑巩—施秉—黄平—麻江—都匀—独山一带，下寒武统牛蹄塘组优质页岩厚度大（50~140m）、有机碳含量高（TOC≥2.0%）、热演化适度（R_O平均2.63%）、埋深适中（1500~4000m）、构造相对稳定，是雪峰古隆起边缘页岩气勘探有利区带。

Abstract:

The study aims to clarify the main controlling factors of shale gas enrichment at the edge of palaeohigh, and guide the evaluation of shale gas effectively in the similar geological conditions, taking the Lower Cambrian Niutitang Formation on the southwestern margin of Xuefeng uplift as an example, combined with the latest exploration data and previous understanding, the enrichment laws of shale gas are discussed further through the comprehensive research on sedimentary facies, evolution history and preservation conditions. The following results were obtained:(1) The shale in lower strata of Niutitang Formation is deposited in deep-water shelf facies. With the participation of hydrothermal activities, the shale possesses high organic matter abundance, Type-I kerogen, rich hydrothermal silicon and high brittle minerals was developed, which has the material basis for shale gas enrichment. (2) The thermal evolution degree has reached an overmature stage, but the organic matter is not carbonification, hence the hydrocarbon generation evolution and the reservoir evolution achieved the best match, which has the prerequisite of shale gas enrichment. (3) The preservation conditions are key factors for shale gas enrichment, which have undergone multiple phases tectonic reworking since the Yanshanian. Based on the above understanding, the criteria for evaluation of shale gas area selection on the southwestern margin of Xuefeng uplift are established. The Cengong-Shibing-Huangping-Majiang-Duyun-Dushan belt has the high-quality shale with great thickness (50~140m), high organic carbon content (TOC ≥ 2.0%), suitable thermal evolution (the average value of R_O is 2.63%), moderate burial depth (1500~4000m), and relatively stable structures, which is proposed favorable zones for Niutitang Formation shale gas exploration.