百色盆地东部古近系那读组湖相灰岩储层特征

Characteristics of the Lacustrine Limestone Reservoir in the Paleogene Nadu Formation, Eastern Bose Basin, Guangxi

湖相碳酸盐岩储层是一个新的油气勘探领域,其研究程度还比较低。本文以百色盆地那坤地区那读组三段下部的湖相灰岩为研究对象,在实测剖面和详细观察岩心的基础上,从岩石学特征、沉积相特征及储集空间类型、孔隙结构类型、储集物性特征等方面详细研究了湖相灰岩的储层特征。指出储集岩主要为各种类型的颗粒灰岩,沉积相以颗粒滩相为主,储集空间类型主要为粒间溶孔和铸模孔,以单一介质的中、细喉(即中小孔结构组合)为主,储层孔隙度主要介于5%～25%之间,渗透率基本上小于1×10-3μm2,滩核微相储集岩的孔隙度和渗透率最高。并从储层孔隙度和渗透率的分布特征及二者间的相关性研究了储层物性的下限值和储层类型划分的界线值,将研究区储集岩划分为4种基本类型。

The carbonate reservoir in lacustrine facies, a new field in oil and gas exploration, has not been thoroughly studied yet. This paper deals in detail with the lacustrine limestone developed in the lower part of the third member of Paleogene Nadu Formation in Nakun area, eastern Baise basin, Guangxi. Based on observations of cores and measured profiles, the authors studied characteristics of lacustrine limestone in such aspects as features of petrology and sedimentary facies, types of reservoir space and pore structure and petrophysical properties. The reservoir rocks consist mainly of all kinds of grained limestone, and the grained beach in the shallow lake is the main part of the sedimentary facies. The reservoir pore space is mainly made up of moldic pores and intergranular dissolved pores, with medium or small throats and pore configuration in a single medium. The porosity is mainly in the range of 5 % - 25 %, and the permeability is smaller than 1×10^-3μm^2. Among all microfacieses, the beach ridge has the largest porosity and permeability. According to the distribution of porosity and permeability and their correlation, the lower limit of reservoir physical properties and the threshold value for classification of reservoir types are studied. In this paper, the reservoir rocks in this area are classified into four basic types, i.e., the low porosity and low permeability reservoir, the medium-low porosity and medium-low permeability reservoir, the medium-high porosity and medium-hlgh permeability reservoir, and the high porosity and high permeability reservoir. The first two are well developed and distributed widely while the last two are poorly developed and only exist in the grained limestone of beach ridge and beach edge.