三塘湖盆地哈尔加乌组火山岩储集层孔隙特征及成因

低温氮气吸附实验是研究致密储集层微观结构特征的重要手段之一,目前在碎屑岩致密储集层研究中取得了较好的效果。应用低温氮气吸附实验,研究三塘湖盆地石炭系火山岩致密储集层纳米级孔隙的成因。实验分析表明：三塘湖盆地上石炭统哈尔加乌组火山岩低温氮气吸附等曲线以墨水瓶形为主,随着深度增加,样品的平均孔径逐渐减小,总孔体积逐渐增大,样品比表面积逐渐增大,表征孔隙表面粗糙程度的分形维数也增大。结合场发射扫描电镜分析表明,三塘湖盆地哈尔加乌组火山岩致密储集层的微观孔隙结构形态与溶蚀作用有关,储集层埋藏越深,介于火山岩内部的烃源岩生成的有机酸越多,溶蚀作用就越强烈,长石等不稳定矿物溶蚀以后,形成新的矿物在喉道沉淀,一方面增加储集层的微观孔隙体积,另一方面降低了储集层渗透率。

Characteristics and Genesis of Pores in Volcanic Reservoirs of Haerjiawu Formation in Santanghu Basin

As one of the important methods to study the microscopic pore structure of tight reservoirs, low-temperature nitrogen adsorption experiment has achieved better application in tight clastic reservoirs. This paper takes the Carboniferous volcanic reservoirs in the Santanghu basin as a case to study the genesis of nano-pores in tight reservoirs by applying low-temperature nitrogen adsorption experiment. Experimental analysis shows that the low-temperature nitrogen adsorption curve of the volcanic rock in the Upper Carboniferous Haerjiawu formation of the Santanghu basin is like a “ink bottle”; as the sampling depth increases, the average pore diameter of the samples decreases, the total pore volume increases, the specific surface area increases, and the fractal dimensionality that can characterize the roughness of the pore surface increases too. Further combination with field emission scanning electron microscopy analysis shows that the microscopic pore structure and morphology of the tight volcanic reservoirs of the Haerjiawu formation in the Santanghu basin is related to dissolution. The deeper the reservoir is buried, the more organic acid is produced by the source rock inside the volcanic rock, and the stronger the dissolution is. After unstable minerals such as feldspar are dissolved, new minerals form and then precipitate near pores and throats. This can increase the microscopic pore volume of the reservoirs and reduce their permeability.