渝东南地区五峰组—龙马溪组页岩含气性差异主控因素及资源潜力评价

    Main controlling factors for variations in gas content and resource potential assessment of the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation shale, Southeastern Chongqing

    • 摘要:
      研究目的 页岩含气性评价对页岩气勘探开发意义重大,其相关参数是资源评估、区带优选、目标刻画及开发规划的关键。
      研究方法 以渝东南地区五峰组—龙马溪组一段页岩为对象,综合现场测试、实验分析和测井解释手段,剖析其含气性影响因素。
      研究结果 研究显示,该地区页岩含气性在纵、横向上差异显著。纵向上,上部⑥~⑨小层总含气量为0.33~4.30 m3/t,均值 1.47 m3/t;下部①~⑤小层总气含量为 0.77~10.88 m3/t,均值 3.55 m3/t,自上而下含气性增强。平面上,盆外、盆缘、盆内优质页岩段总含气量均值分别为 3.04 m3/t、3.46 m3/t、4.27 m3/t,从盆外至盆内,含气性变好,单井产量递增。
      结论 影响页岩含气性的因素分静态与动态2类。页岩储层品质是基础性静态因素,如沉积环境、岩性、TOC 含量等,决定了原始生烃和供烃能力。保存条件是关键性静态因素,包括埋藏深度、与剥蚀区距离、断裂性质等,影响地层压力系数与页岩气保存。成藏演化是决定性动态因素,构造变形和页岩气逸散时间差异,改变总含气量与游离气占比,进而影响单井产量。依据物质基础、保存条件、含气性等关键参数,综合评价出渝东南地区页岩气资源量2.06×1012 m3,其中Ⅰ类区资源量3 458×108 m3

       

      Abstract:
      Objective The evaluation of shale gas−bearing properties plays a pivotal role in shale gas exploration and development. The associated parameters are fundamental for resource assessment, prospective zone prioritization, delineation of sweet spot targets, and formulation of development plans.
      Methods This study focuses on the Wufeng Formation−First Member of Longmaxi Formation shale in Southeastern Chongqing. By integrating multiple methods including field tests, laboratory analyses, and well logging interpretation, the influencing factors of its gas−bearing capacity were analyzed.
      Results The research findings indicate that the gas−bearing properties of the shale in this region exhibit pronounced variations both vertically and horizontally. Vertically, the total gas content of sub−layers ⑥~⑨ ranges from 0.33 to 4.30 m3/t, with an average of 1.47 m3/t. In contrast, that of sub−layers ①~⑤ spans from 0.77 to 10.88 m3/t, averaging 3.55 m3/t. Evidently, the gas−bearing properties enhance from the upper layers to the lower ones. Horizontally, the average total gas content of the high−quality shale segments outside the basin, along the basin margin, and within the basin amounts to 3.04 m3/t, 3.46 m3/t, and 4.27 m3/t respectively. Moving from the exterior to the interior of the basin, the gas−bearing properties progressively improve, accompanied by a successive increase in single−well production.
      Conclusions The factors influencing the gas−bearing properties of shale can be categorized into static and dynamic types. The quality of the shale reservoir represents a foundational static factor. Variables such as the sedimentary environment, lithology, and total organic carbon (TOC) content determine the original hydrocarbon generation and supply capacities. Preservation conditions, a crucial static factor, encompass parameters like burial depth, distance from the erosional zone, and fault characteristics. These conditions exert a significant influence on the formation pressure coefficient and the retention of shale gas within the reservoir. Reservoir formation and evolution constitute decisive dynamic factors. Disparities in the timing of tectonic deformation and shale gas escape lead to alterations in the total gas content and the proportion of free gas, ultimately impacting single−well production. Based on key parameters including material basis (source rock conditions), preservation conditions, and gas−bearing properties, the total shale gas resources in Southeastern Chongqing are comprehensively evaluated to be 2.06 × 1012 m3, of which the resources within the Class I area amount to 3458 × 108 m3.

       

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