渤海湾盆地北塘凹陷古近系沙河街组三段白云岩储层特征

渤海湾盆地北塘凹陷古近系沙河街组三段白云岩分布广泛,是重要的油气储集层。根据钻井岩心、岩石薄片、扫描电镜、电子探针和地球化学特征等资料,对沙三段白云岩储层特征及其影响因素进行了详细研究。结果表明,沙三段白云岩有层状、结核状、均匀块状和裂缝充填等4种产状,岩石类型包括泥晶白云岩、粉晶白云岩和细晶白云岩,储集空间主要为次生孔隙和裂缝;白云岩储层物性较差,孔洞缝共同发育的层段是油气富集的有利层段,储层的含油性与储层的岩性及物性具有一定的相关性。目前白云岩储层正处于中成岩阶段,在埋藏过程中经历了机械压实、压溶、胶结、溶蚀、重结晶和白云岩化等成岩作用的改造,其中溶蚀作用可分为三期,后两期溶蚀作用极大地改善了储层物性,机械压实和胶结作用对储层物性起破坏作用;地球化学特征揭示了白云岩化作用的两种类型,即准同生期的回流渗透白云岩化和成岩期的埋藏白云岩化。影响白云岩储层物性的主要因素包括沉积环境、白云岩化作用和裂缝发育程度,沉积环境对白云岩储层物性起决定性作用,白云岩化作用对储集空间具有重要的改造作用,裂缝的发育极大改善了储层物性,提高了储层的储集能力。

Characteristics of Dolostone Reservoir in Sha 3 Group from Palaeogene Shahejie Formation in Beitang Sag, Bohaiwan Basin

Dolostone is widely distributed in third section of Palaeogene Shahejie Formation from Beitang Sag in Bohaiwan Basin, which can develop good reservoir properties.In this paper, based on a vast amount of data from core drilling, rock thin sections, scanning electron microscope, electron probe and geochemistry characteristics, we study the characteristics and influencing factors of Sha 3 dolostone reservoir of Palaeogene Shahejie Formation in detail.Dolostone has four types of occurrence, including layered, nodular, massive and fracture filled.It is showed that the Sha 3dolostone reservoir rock types are mainly micrite dolostone, crystal powder dolostone and aplite dolostone.Reservoir space of Sha 3 dolostone reservoir mainly consists of dissolved intergranular pore and fractures.Dolostone reservoir is characterized by poor physical property, and the layer section with pores, caves and fractures can be performed as hydrocarbon enrichment zones.The oiliness of Sha 3 dolostone reservoir has a certain correlation with lithology and physical properties.The Sha 3 dolostone reservoir is now in the stage of mesodiagenesis, and the main diagenesis of which mainly including mechanical compaction, pressure solution, cementation, dissolution, recrystallization and dolomitization.Dissolution can be divided into three stages, and the latter two stages of dissolution lead to improve physical properties of dolostone reservoirs, while mechanical compaction and cementation result in the reducing of physical properties.Geochemistry characteristics reveal two types of dolomitization: penecontemporneous seepage reflux dolomitization and deep buried diagenetic dolomitization.Physical property of dolostone reservoir is mainly influenced by sedimentary environment, dolomitization and fracture development.Sedimentary environment plays a decisive role on the quality of dolostone reservoir and dolomitization plays an important role on the modification of reservoir space.Huge amount of fractures improves physical properties and enhances the reservoir capability of dolostone reservoir.