低渗砂岩气藏储层物性与孔喉结构分析

采用铸体薄片、扫描电镜和岩石矿物含量与结构分析技术,结合岩样压汞资料等多种技术手段,对荷包场—界市场(简称包界)试验区须家河组气藏储层的物性特征和微观孔喉结构进行了深入分析和研究。研究发现储层孔隙类型以原生残余粒间孔、次生粒间孔隙和混合孔隙为特征。当孔隙度大于7%时,储层孔隙以粒间孔为主,其喉道类型以缩颈喉道为主,次为片状喉道;当孔隙度小于7%时,孔隙以粒内溶孔为主,其喉道类型以片状喉道为主,次为管状喉道;储层内粘土矿物含量较高,伊利石呈片状、丝缕状桥接孔隙,造成对孔隙、喉道的堵塞或封隔,使孔隙的连通性进一步降低。孔喉分布总体具有单峰状,以小孔细喉型为主体,平均中值喉道半径小,渗透率贡献值与喉道分布不一致,岩样渗透性主要由少数粗喉道提供,占据大部分比例的小喉道对岩样渗透性的贡献极小。鉴于储层含水饱和度较高、气井产凝析油以及粘土含量高的现象,建议尽量保持地层压力以防止凝析油过早析出,降低经济极限产量以提高低渗、特低渗区储层的动用能力。

Physical Characteristics and Pore Throat Structure Analysis of Low Permeability Sandstone Gas Reservoir in Xujiahe Formation of Baojie District

Aiming at the low permeability sandstone gas reservoir in Xujiahe Formation of Sichuan basin and adopting the casting slice,scanning electron microscope,rock mineral content and rock pore structure analysis technology,this paper made a systemic and deep analysis for the microcosmic pore structure and physical characteristics of the gas reservoir combined with high pressure mercury data.Though some high porosity reservoirs exist in local district of Sichuan basin,they belong to the low porosity,low permeability and extraordinary low permeability tight gas reservoir,and water saturation is high.The research finds that pores can be divided into three types:crude residual intergranular pore,induced pore and mixed pore.When the porosity exceeds 7%,the residual intergranular pore is the main pore type,and the retractile throat is the main throat type.When the porosity is below 7%,the granular solution pore is the main pore type,and the tubular throat is the main throat type.Clay content of gas reservoir is high,the clay takes on the scaly,silk-thread form, bridging the pore and clogging or plugging the pore structure and throat.The small pore and fine throat is the main type in the reservoir,the average median throat radius is small.The contributing value of throat to permeability is not proportional to the throat distribution.A small quantity of large throats offer the reservoir permeability,and small throats which occupy a large space offer little for the reservoir permeability and the permeability is offered by the large throat which occupy a large space.Considering the high water saturation,gas condensate and high clay content,the key measure is to reduce the economic limit of gas production and prolong the low pressure,low production period in order to improve the employing ability of the low permeability,specifically-low permeability reservoir.