渝西区块页岩气储集层微观孔-缝配置类型及其地质意义

Microscopic pore-fracture configuration and gas-filled mechanism of shale reservoirs in the western Chongqing area, Sichuan Basin, China

以渝西区块上奥陶统五峰组—下志留统龙马溪组页岩储集层为研究对象,开展氩离子抛光扫描电镜及饱和不同润湿介质核磁共振实验,结合图像处理技术与现场解吸结果,分析微观孔-缝配置类型及其对页岩气赋存机制的影响。结果表明:(1)储集空间包括有机孔、无机孔和微裂缝,微裂缝发育特征的井间差异明显,有机孔发育程度与毗邻微裂缝的距离成反比,而无机孔则正好相反;(2)依据有机孔、微裂缝发育类型、程度及相互接触关系,将孔-缝配置类型划分为4类;(3)根据饱和油、水核磁T2谱差异构建并计算孔-缝配置的评价参数,其值越小,孔-缝配置越好;(4)孔-缝配置好的页岩储集层具有有机孔发育、孔隙度高、渗透率高、含气性高的特点,而孔-缝配置差的页岩则表现为微裂缝相对发育,增强了天然气输导能力,导致孔隙度和含气性偏低;(5)基于孔-缝配置类型,从有机质生烃、微裂缝提供运移通道的角度出发,建立3类页岩气微观赋存模式。图8表3参38。

Taking the Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation shale reservoirs in western Chongqing area as the study target, the argon ion polishing scanning electron microscope and nuclear magnetic resonance(NMR) experiments of different saturated wetting media were carried out. Based on the image processing technology and the results of gas desorption, the pore-fracture configuration of the shale reservoirs and its influence on gas-filled mechanism were analyzed.(1) The reservoir space includes organic pores, inorganic pores and micro-fractures and there are obvious differences between wells in the development characteristics of micro-fractures;the organic pores adjacent to the micro-fractures are poorly developed, while the inorganic pores are well preserved.(2) According to the type, development degree and contact relationship of organic pore and micro-fracture, the pore-fracture configuration of the shale reservoir is divided into four types.(3) Based on the differences in NMR T2 spectra of shale samples saturated with oil and water, an evaluation parameter of pore-fracture configuration was constructed and calculated. The smaller the parameter, the better the pore-fracture configuration is.(4) The shale reservoir with good pore-fracture configuration has well-developed organic pores, high porosity, high permeability and high gas content, while the shale reservoir with poor pore-fracture configuration has micro-fractures developed, which improves the natural gas conductivity and leads to low porosity and gas content of the reservoir.(5) Based on pore-fracture configuration, from the perspective of organic matter generating hydrocarbon,micro-fracture providing migration channel, three types of micro gas-filled models of shale gas were established.