罗子沟盆地有机质热演化对砂岩物性的改造作用

Effect of Organic Thermal Evolution on Physical Characteristics of Sandstone in Luozigou Basin

基于岩石薄片观察、压汞分析、扫描电镜和X衍射分析等方法对罗子沟盆地大砬子组砂岩物性特征进行了定性-定量研究。结果表明：罗子沟盆地大砬子组砂岩成分成熟度和结构成熟度低,以岩屑长石砂岩和长石砂岩为主;岩石孔隙度高,孔隙度主要为16.2%-26.4%,次生孔隙占总孔隙度面孔率的88%,但总体渗透率极低,渗透率主要分布在（0.13-1.68）×10^-3μm^2,为高孔特低渗的物性特征。有机元素分析、色谱分析、岩石热解及显微组分镜检分析表明,罗子沟盆地大砬子组泥页岩中有机质在热演化过程中产生大量有机酸,有机酸对砂岩中长石等矿物的溶蚀作用是次生孔隙发育的主要原因,但有机酸溶蚀产生的次生矿物在一定程度上堵塞了孔隙喉道。因此,研究区砂岩形成高孔特低渗的物性特征。

Physical characteristics of sandstone in Luozigou basin were studied qualitatively and quantitatively with thin sections,mercury intrusion,SEM,X-ray diffractions and some other methods. Results show that the main lithological types of Dalazi Formation are lithic arkose and arkose with low compositional maturity and low textural maturity.The physical characteristics of sandstone were characterized by high porosity（16.2%to 26.4%）and very low permeability（0.13×10^-3 μm^2 to 1.68× 10^-3 μm^2）,and the porosity type was mainly secondary pores which accounst for 88% of the whole porosity.Result of organic element analysis,chromatography,maceral microscopy and rock pyrolysisshowed that large amounts of organic acids generated during the thermal evolution of mudstone and shale in Luozigou basin and dissolute feldspar in sandstone,which lead to high secondary porosity.While,at the same time,associated products of the dissolution blocked the throat to some extent.These two processes make the sandstones show high porosity and low permeability.