中基性岩系火山地层、架构和储层:松辽盆地埋藏古火山与长白山现代火山对比研究

Volcanostratigraphy,volcanic architecture and reservoir of intermediate-mafic volcanic rocks:A comparison between buried Cretaceous volcanoes in the Songliao Basin and the modern volcanoes in Changbai Mountain

松辽盆地白垩纪埋藏古火山是深层天然气的主要储集体,储层岩性既有酸性岩又有中基性岩系;长白山是第四纪形成的以中基性岩类为主的现代火山。对二者的岩性、岩相、地球化学和火山学的对比研究发现,孔隙度大于60%的浮岩类在长白山现代火山广泛发育,而在松辽盆地埋藏古火山中迄今没有发现,这是盆地火山岩埋深成岩作用对原生孔隙改造的结果。长白山火山各个喷发期次之间普遍发育砂砾质堆积物形成的夹层,通常称之为"松散层",它们是火山喷发间歇期火山地貌受外动力地质作用改造、各种粒度和成分的沉积物近源堆积的结果。松辽盆地火山岩油气勘探中,"界面控储"是储层发育的普遍规律,意即优质储层多出现在火山地层界面附近。二者对比研究表明,界面控储与松散层密切相关。松辽盆地白垩纪火山岩系在长期的形成演化过程中,各喷发期次之间不仅有松散层,还发育有一系列风化剥蚀面。因此推断,松散层及其附近的风化面是火山地层界面控储的地质成因。这些层段具有多种孔隙-裂缝组合,容易形成连通的储集空间网络系统,是高孔、高渗型火山岩有效储层的有利发育部位。

The Cretaceous buried volcanoes are the main reservoirs of deep oil&gas in the Songliao Basin.The reservoir lithology includes both acidic and intermediate-mafic volcanic rocks.The Changbai Mountains are modern volcanoes developed in the Quaternary period and dominated by intermediate-mafic volcanic rocks.Through a comparative study of lithology,lithofacies and volcanology,it was found that pumice with a porosity of more than 60%was widespread in the modern volcanic area,but these rocks could not be found near the buried volcanoes in the Songliao Basin.This is the result of burial diagenesis affecting the porosity of the volcanic rocks in the basin.The interlayers formed by gravel deposits are commonly developed between various eruptive stages of the Changbai Mountain volcano and are often referred to as loose layers;they are the result of near-source accumulation of sediments of various particle sizes and components due to the volcanic geomorphology and external geodynamics.For oil and gas exploration in the Songliao Basin,volcanostratigraphic boundaries control the reservoir distribution.A comparative study revealed that the distribution of reservoirs is under the control of volcanostratigraphic boundaries,which is closely related to the loose layers.During the long-term formation and evolution of the Cretaceous volcanic rocks in the Songliao Basin,loose layers and a series of weathered and degraded surfaces were deposited between each eruption period.Therefore,it is inferred that the loose layers and the weathered surfaces are the control on the petroleum reservoirs.Because these intervals have a variety of pore-crack combinations,they easily form a connected reservoir network system and are favorable sites for the development of high-porosity and high-permeability volcanic reservoirs.This type of volcanic reservoir and its hydrocarbon reservoirs have good identifiability in logging data due to characteristic seismic reflection properties.They are usually characterized by high gamma,low resistance,and low density logs.Moreover,they exhibit a combination of lower truncation and the upper drape-upper phases in seismic reflection cross-sections.