鄂尔多斯盆地临兴地区下石盒子组成岩作用类型及其对油气储层的控制作用

Type of diagenesis and its controlling effect on oil and gas reservoirs in the Xiashihezi Formation in Linxing district,Ordos Basin

本文通过大量岩石薄片、扫描电镜及阴极发光等的观察,分析了临兴地区下石盒子组成岩作用类型、成岩作用对物性的影响以及与油气分布规律的关系。结果表明,研究区下石盒子组成岩作用主要包括压实作用以及胶结弱溶蚀;而且压实作用大大降低了原生孔隙体积,胶结作用堵塞了孔隙和喉道,溶蚀作用提高了砂岩的储集性能。成岩作用在砂体不同部位的差异是形成岩性圈闭的条件,纵向上水下分流河道、河口坝底部和顶部为低渗储层,中部位为渗透层,因此水下分流河道和河口坝砂体可成为一套岩性圈闭;在平面上原生孔+次生孔相和次生孔相分布于水下分流河道和河口坝等分选较好,粒度较粗的微相中。分选较差、粒度较细的远砂坝和席状砂微相发育的砂岩杂基含量较高,主要为低渗砂岩,为油气富集区形成横向遮挡条件。总体上来说,沉积相为水下分流河道和河口坝微相,成岩相为原生孔+次生孔相以及次生孔相为有利的储层,是油气的最为有利聚集场所,其次为远砂坝和席状砂微相,成岩相为自生高岭石充填粒间孔相和胶结弱溶蚀相的储层,含气性相对较差。

The authors analyze the influence of diagenesis and diagenesis types on physical properties,and relationships between diagenesis and distribution pattern of oil and gas in the Xiashihezi Formation in Linxing area though observing lots of rock slice,scanning electron microscope and cathodoluminescence.Diagenesis types include compaction,cementation and weak dissolution;Compaction greatly destroys primary pore volume,cementation blocks pores and throats,dissolution improves the reservoir quality of the sandstones in the Xiashihezi formation.The condition of forming lithologic trap are the diagenesis differences in different part of the sand,in the vertical of which,the bottom and top of subsea distributary channel and the mouth bar faces are low permeable and the middle are permeable formation,hence,subsea distributary channel and the mouth bar faces sands can make a lithilogic trap;In the plane,the primary pore and the secondary pore facies,the secondary pore facies spread over subsea distributary channel and mouth bar facies,which have preferable sorting and rough granularity.sand with higher matrix are impermeable to keep oil and gas out the plane area in the far bar and sheet sand faces with worse sorting and thinner granularitymainly.The sandstone with higher matrix in distal bar and sheet sand microfacies,which have worse sorting and thinner granularity,are hypotonic,it＇s keeping oil and gas out the plane area.As a whole,reservoir with subsea distributary channel and mouth bar microfacies,meanwhile,the primary pore and the secondary pore facies,or the secondary pore is the beneficial sites for hydrocarbon accumulation,then,gas-bearing properties of reservoirs with distal bar and sheet sand microfacies,meanwhile,authigenic kaolinite inter grain pores diagenetic facies or cementation and weak dissolution facies,are poor.