桂中坳陷页岩气调查进展、挑战与勘探方向

    Shale gas survey progress, challenges and exploration direction in Guizhong Depression

    • 摘要: 桂中坳陷是四川盆地外围页岩气勘探的重要新区,但复杂构造背景与地表条件制约了其勘探进程。为系统总结该区公益性页岩气地质调查成果, 厘清关键问题并明确突破方向,基于2012年以来公益性地质调查成果,全面梳理桂中坳陷泥盆系—石炭系页岩气地质调查历程,划分勘查阶段,总结富有机质页岩地质特征,剖析存在的问题与挑战。结果表明,下石炭统鹿寨组为区内主力页岩气勘探层系,多口钻井获页岩气显示,并已形成页岩气勘查区块成功出让。公益性地质调查工作历经起步、发展、突破3个阶段,初步打通“地质调查—钻探验证—资源评价—区块出让”的完整勘查链条。同时,勘查工作仍面临沉积相变快且有机质富集特征不明、多期构造改造导致保存条件复杂、碳酸盐岩覆盖区地震成像品质低、喀斯特地貌钻探工程适应性差4方面制约。针对上述问题,提出“拓展层系—深化机理—技术升级”的下一步勘探思路,即夯实石炭系主力层系并拓展接续层系,深化优势相带刻画与保存条件评价,攻关碳酸盐岩区综合地球物理勘查技术。桂中坳陷页岩气调查实践表明,公益性地质调查在复杂构造区海相页岩气勘探中发挥着基础性、先行性作用,可为同类地区的页岩气勘查提供参考。

       

      Abstract: The Guizhong Depression represents a significant new area for shale gas exploration in the periphery of Sichuan Basin. However, its exploration progress has been constrained by the complex structural setting and surface conditions. In order to systematically summarize the achievements of public welfare geological surveys for shale gas in this area, identify key issues, and define breakthrough directions, the authors in this paper have comprehensively reviewed the history of the Devonian-Carboniferous shale gas geological surveys in Guizhong Depression based on public welfare geological survey data since 2012. The exploration stages were delineated and the geological characteristics of organic-rich shales were summarized. Besides, the existing problems and challenges were analyzed. The results showed that Luzhai Formation in the Lower Carboniferous was the primary shale gas exploration target in Guizhong Depression. Multiple wells have encountered shale gas shows, and exploration blocks have been successfully auctioned. The public welfare geological survey efforts have progressed through three stages-initiation, development, and breakthrough, and a complete exploration chain was preliminarily established, including geological survey-drilling verification-resource assessment-block auction. Nevertheless, exploration still faces four major constraints, that is rapid sedimentary facies changes with unclear organic matter enrichment characteristics, complex preservation conditions caused by multi-stage tectonic reworking, low seismic imaging quality in carbonate-covered areas, and poor drilling adaptability in karst landforms. In response to these challenges, the authors proposed a future exploration strategy, which was expanding stratum-deepening mechanism-upgrading technology. The exploration strategy included consolidating the Carboniferous as the primary target while expanding the succeeding exploration strata, deepening the characterization of favorable facies belts and preservation condition assessment, and tackling integrated geophysical exploration techniques in carbonate areas. The shale gas exploration practice in Guizhong Depression indicates that the public welfare geological survey has played a pioneering and fundamental role in marine shale gas exploration and development in complex structural areas, providing references for shale gas exploration.

       

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