川南泸州地区龙马溪组一段有机质页岩裂缝发育特征及有利区评价

Development characteristics and favorable area evaluation of organic-rich shale fractures in first member of Longmaxi Formation, Luzhou area, southern Sichuan Basin

  • 摘要: 四川盆地南部地区志留系龙马溪组一段页岩气,具有良好的勘探开发前景。为了探明页岩天然裂缝发育特征对页岩气富集规律的影响,选取川南泸州地区龙马溪组一段有机质页岩为研究对象,基于钻井岩心、薄片鉴定、地球物理测井等资料,运用地质综合分析方法,对研究区龙马溪组页岩的裂缝类型及发育特征开展研究。川南泸州地区龙马溪组一段有机质页岩裂缝类型主要为构造缝(剪切缝)和非构造裂缝。构造因素上,裂缝的发育程度与距断层距离呈负相关关系,且背斜区裂缝发育程度较高,向斜区裂缝发育程度较低。非构造因素上,裂缝密度与总有机碳含量(≥2%)和脆性矿物含量(≥44%)均呈正相关关系。研究区有机质页岩含气性则受裂缝充填程度、现今地应力方向与裂缝走向关系、裂缝分散程度等因素影响,其中半充填和未充填裂缝、与现今最大主应力大角度斜交的裂缝及走向分散的裂缝网络显著提升页岩含气性。研究将川南泸州地区龙马溪组一段有机质页岩有效裂缝划分为6个Ⅰ类有利区和7个Ⅱ类有利区,明确了背斜区及断裂带附近为勘探靶区,为川南泸州地区页岩气勘探与开发提供了重要的理论支撑和实践指导。

     

    Abstract: The shale gas in the first member of the Silurian Longmaxi Formation in the southern Sichuan Basin exhibits promising potential for exploration and development. To clarify the influence of the development characteristics of natural fractures in shales on shale gas enrichment patterns, the organic-rich shales in the first member of the Longmaxi Formation in the Luzhou area, southern Sichuan Basin were selected as the study objects. Utilizing drilling cores, thin-section identification, and geophysical well logging data, this study investigated the types and development characteristics of fractures in the Longmaxi Formation shales in the study area through comprehensive geological analysis methods. The results showed that the fracture types were mainly structural fractures (shear fractures) and non-structural fractures. Structurally, the degree of fracture development was negatively correlated with the distance from faults, with fractures being well-developed in the anticline areas and less developed in the syncline areas. In terms of non-structural factors, fracture density was positively correlated with total organic carbon content (≥2%) and brittle mineral content (≥44%). The gas-bearing capacity of organic-rich shales in the study area was affected by factors such as the degree of fracture filling, the relationship between the current in-situ stress direction and the fracture strike, and the degree of fracture dispersion. Among these, partially filled and unfilled fractures, fractures intersecting with the current maximum principal stress at high oblique angles, and fracture networks with scattered strikes significantly enhanced the gas-bearing capacity of shales. This study divided the effective fractures in the organic-rich shales of the first member of the Longmaxi Formation in the Luzhou area of the southern Sichuan Basin into 6 Class Ⅰ favorable areas and 7 Class Ⅱ favorable areas. It identified the anticline areas and areas adjacent to fault zones as the exploration target areas. These findings provide important theoretical support and practical guidance for the exploration and development of shale gas in the Luzhou area of the southern Sichuan Basin.

     

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