鄂尔多斯盆地靖边气田砂岩储层成岩作用

Diagenesis of Sandstone Reservoirs in Jingbian Gas Field, Ordos Basin

靖边气田二叠系砂岩储层的低孔低渗特征成为严重困扰该区天然气生产的关键问题,为了分析该区储层物性变差的主要原因,提高储层预测精度,本文通过系统的薄片鉴定、压汞、阴极发光、扫描电镜等分析,研究了该区砂岩的成岩作用及其对储集性能的控制作用。研究发现,靖边气田盒8段砂岩主要为岩屑砂岩、岩屑石英砂岩和石英砂岩,胶结物主要为碳酸盐、高岭石、绿泥石和硅质胶结,碳酸盐胶结物含量对储层物性影响较大;储集空间主要是剩余原生粒间孔、粒间溶孔、粒间溶蚀扩大孔、粒内溶孔、高岭石晶间孔及少量微裂缝,以次生孔隙为主;盒8段砂岩主要为II、III类储集岩,I类储集岩较少。研究认为,沉积微相奠定了储层的物质基础,决定储层的空间展布,而成岩作用改造是储层物性好坏的关键因素,二者共同决定了储层的发育程度。压实作用和胶结作用是储层物性变差的最主要原因,广泛发育的铝硅酸盐矿物溶解对储层物性的改善起关键作用。

The low porosity and low permeablity of Permian sandstone reservoirs are the key puzzling issues in gas exploitation in Jingbian gas field, Ordos basin. To analyze the poor property of sandstone reservoirs and improve the accuracy of reservoir forecast, the diagenesis and its controls on reservoir property of sandstone in this area are studied by using systematic slice identification, mercury penetration,cathodoluminescence and scanning electron microscope. It is shown that lithology of P2h8 sandstone in Jingbian gas field is dominated by lithic sandstone, lithic silicarenite and silicarenite with carbonate, gaolinite, chlorite and siliceous cementation. Content of carbonate cementation influences greatly the properties of reservoirs. Reservoir space is domanited by secondary porosity, including the remaining primary intergranular pores, intergranular dissolution pores, intergranular corrosion expanding pores, intragranular dissolved pores, intergranular pores in Kaolinite, and some micro-cracks. Sandstone reservoirs in P2hs consist mainly of rocks of type II and type III with small portion of rocks of type I. The sedimentary microfacies and the diagenesis controlled development of reseroirs are considered as the main material basis of reservoirs. Well diagenesis aheration is the key factor that determines properties of reservoirs. Compaction and cementation are the main controls on degrading physical properties of reservoirs. Extensively developed dissolvement of aluminosilicate minerals plays a key role in improving properties of reservoirs.