准噶尔盆地深层煤岩特征及含气量测井解释方法研究——以滴南–白家海区块西山窑组、八道湾组煤岩为例

Characteristics of Deep Coal Rock and Logging-Based Interpretation Method for Gas Content—A Case Study of the Xishanyao and Badaowan Formations in the Dinan-Baijiahai Block, Junggar Basin

摘要: 深层煤岩气为非常规油气开采领域的热点，但存在煤岩特征不清以及基于浅层煤层气储层含气量测井评价模型精度低等问题，亟需开展煤岩特征及含气量测井解释评价方法研究。以准噶尔盆地滴南–白家海区块侏罗系西山窑组、八道湾组深层煤岩为研究对象，综合岩心、物性以及扫描电镜等分析化验资料，系统研究煤岩的煤阶、宏观煤岩类型、工业组分、孔–裂隙特征、物性以及含气性等特征，建立深层煤岩含气量测井解释评价模型。结果表明：(1) 研究区煤岩镜质体反射率介于0.43%~0.85%之间，主要为长焰煤和气煤，属中低煤阶。西山窑组主要为半暗–半亮型煤，结构以原生–碎裂结构为主；八道湾组煤岩以半亮–光亮型为主，主要发育原生结构；(2) 西山窑组为低–中挥发分、特低灰分、中–高固定碳煤；八道湾组为中–高挥发分、低灰分、低–中固定碳煤；(3) 储集空间类型以胞腔孔、气孔和裂隙为主，其中裂隙以割理及微裂缝为主；(4) 西山窑组煤岩孔隙率介于10.48%~21.47%之间，平均值为15.71%，渗透率介于(0.98~23.82) × 10⁻³ μm²之间，平均值为6.67 × 10⁻³ μm²，属中–高孔隙率、中–高渗透率储层；八道湾组煤岩孔隙率介于0.95%~3.88%之间，平均值为3.00%，渗透率介于(0.0044~0.0681) × 10⁻³ μm²之间，平均值为0.028 × 10⁻³ μm²，属低孔–低渗类储层；(5)优选敏感测井曲线，构建西山窑组、八道湾组深层煤岩总含气量复合参数(G_x、G_b)。根据总含气量与复合参数的关系，建立含气量测井解释模型。相较于多元线性回归模型，采用复合参数的含气量测井解释模型，表现出较高的准确性和良好的适用性，应用前景较好。

Abstract: Deep coal-rock gas has become a research focus in the field of unconventional oil and gas exploitation. However, challenges remain, including insufficient understanding of coal-rock characteristics and low accuracy of gas content logging evaluation model derived from shallow coalbed methane reservoirs. Consequently, it is urgent to carry out research on coal-rock characteristics and logging interpretation method for gas content evaluation. This study investigates the deep coal seams of the Jurassic Xishanyao and Badaowan Formations in the Dinan-Baijiahai block of the Junggar Basin. The coal rank, macroscopic coal rock type, maceral composition, pore-fracture characteristics, physical properties and gas content of coal rock are systematically studied by integrating the analysis and test data of core, physical properties and scanning electron microscope. The logging interpretation and evaluation model for gas content in deep coal rock is established. The results show that: (1) The vitrinite reflectance of the coal rock ranges from 0.43% to 0.85%, corresponding to long-flame and gas coals of medium to low coal rank. The Xishanyao Formation is characterized by semi-dark to semi-bright coal with primary-fragmentation structure. The coal rock of Badaowan Formation is mainly semi-bright to bright coal with preserved primary structure. (2) The Xishanyao Formation coals exhibit low to medium volatile matter, ultra-low ash yield, and medium to high fixed carbon content. In contrast, the Badaowan Formation coals are characterized by medium to high volatile matter, low ash yield, and low to medium fixed carbon content. (3) The types of reservoir space are primarily composed of cellular pores, gas pores and fractures, among which cleats and microcracks are the dominant fracture typs. (4) The porosity of Xishanyao Formation rangs from 10.48% to 21.47%, with an average of 15.71%, and the permeability ranges from 0.98 × 10⁻³ μm² to 23.82 × 10⁻³ μm², with an average of 6.67 × 10⁻³ μm², indicating a medium-high porosity and permeability reservoir. The porosity of coal rock in Badaowan Formation ranges from 0.95% to 3.88%, with an average of 3.00%, and the permeability ranges from 0.0044 × 10⁻³ μm² to 0.0681 × 10⁻³ μm², with an average of 0.028 × 10⁻³ μm², indicating a low porosity and permeability reservoir. (5) Sensitive logging curves are optimized to construct composite parameters (G_x for Xishanyao Formation and G_b for Badaowan Formation) representing the total gas conten in deep coal rock. Based on the relationship between total gas content and these composite parameters, a gas content logging interpretation model is established. Compared with the multiple linear regression model, the proposed composite-parameter model demonstrates superior accuracy and good applicability, suggesting promising potential for feild application.