泥云岩储层成因机理及其特征研究——以酒西盆地青西凹陷下沟组泥云岩储层为例

Research on the Formation Mechanisms and Reservoir Characterization of Argillaceous Dolomites and Dolomitic Mudstones Reservoir:a Case Study of Xiagou Formation Qingxi Sag in Jiuxi Basin

酒西盆地青西凹陷白垩系下沟组地层发现的厚层泥质白云岩和白云质泥岩是该区主力生油岩和储集层,这种低孔低渗的致密储层蕴含丰富的油气资源引起了地质学家的重视但是目前对此类非常规储层成因机制和特征的了解有限。利用测钻井、岩心、镜下薄片等资料,通过分析岩石组成构成、统计下沟组g0—g1层泥云岩厚度百分比和镜下描述等方法对泥云岩储层进行研究。由于泥云岩储层位于盆地半深湖—深湖亚相环境,确定巨厚泥云岩的成因机制属于火山口"白烟型"喷流—热液沉积作用与后期深埋藏成岩改造作用。该成因机制导致泥云岩中含有大量钠长石、铁白云石等脆性矿物发育,具有二元纹层和三元纹层的特点,即富有机质的泥岩层与白云岩、长石等脆性矿物构成薄纹层"千层饼"式的薄纹层互层结构。另外,酒西盆地构造活动频繁导致储层内对油气运移和储集有利的裂缝非常发育。对泥云岩储层进行表征,利于理解致密储层富含油气的机理并对下一步泥云岩等致密储层的油气勘探提供帮助。

The thick layers of argillaceous dolomites and dolomitic mudstones are the main source rocks and reservoirs in the Lower Cretaceous strata Xiagou Formation in Qingxi Sag, Jiuxi Basin has caused intensive interest but this unconventional reservoir as yet little known. By using the data of drilling logging, core descriptions and mirco scopic slivers, by analyzing the rock formation,the thickness of argillaceous dolomites and dolomitic mudstones percentages in g0-g1 layer of Xiagou formation are statisticed to study reservoir characterization. Since the argillaceous dolomites and dolomitic mudstones reservoir lies in facies of deep-lack, based on the former studies, determined the formation mechanism is the craterlike ＂white smoke＂ Jet-hydrothermal deposition and controlled by the alternation diadenetic effect to formed the thick muddy dolomite. Due to this genetic mechanism, dolomitic mudstones contains a lot of brittle minerals, such as feldspar, iron dolomite, present the characteristics of dual-laminar and tri-laminares, namely organic matter-rich strata of mud and brittle mineral composition of dolomite, feldspar and other thin laminae in the ＂layer cake＂ model of thin laminae of alternating layer structure. In addition, the tectonic activities resulting in Jiuxi Basin reservoir has lots of fractures which is good for hydrocarbon migration and accumulation. Reservoir characterization of argillaceous dolomites and dolomitic mudstones reservoir, conducive the understanding of the reservoir characteristics which can help to explore ＆ develop the reservoir.