柴西第三纪湖相生物礁储层特征及意义

Reservoir Characteristicsand Significance of Tertiary Lacustrain Reef in Western Qaidam

最近在柴达木盆地西部干柴沟一带发现的第三纪湖相生物礁 ,存在于第三系的下干柴沟组下段到下油砂山组的数千米厚的地层中。在野外露头实测、大量岩石薄片和铸体薄片研究的基础上 ,运用毛细管压力曲线和图象分析等手段 ,对生物礁储层特征作了详细研究。生物礁孔隙类型复杂 ,主要有骨架孔隙、粒内孔隙、铸模孔隙、溶孔等 8种孔隙类型。生物礁经历了同生成岩、早成岩、晚成岩和表生成岩四个阶段。胶结作用和溶蚀作用是孔隙的主要形成作用 ,真正的原生孔隙已很少 ,次生孔隙极其发育 ,是油气的优良储集层。生物礁的发现对于青海油田油气勘探与开发具有重大的现实意义。

In the western Qaidam basin, Tertiary lacustrine reef has been discovered recently in several kilometers strata from the lower member of lower Ganchaigou formation to lower Youshashan formation in Ganchaigou area. On the basis of numerous observations on outcrop, thin sections and casting sections of the reef, and the application of various analytical techniques including analysis of capillary pressure curve and pattern analysis of pore structure, reservoir characteristics of reef have been thoroughly studied. The reef has complex types of pores, such as skeletal pores, intraparticle pores, moldic pores and corroded cavities, and so on. The reef underwent four diagenetic period, such as syngenetic, eogenetic, telogenetic, and hypergene diagenetic period. The formation of the pores are mainly affected by the cementation and dissolution with few primary pores, however, the secondary pores are abundant and form excellent reservoir for oil and gas. The discovery of the Tertiary lacustrine reef in the Qaidam Basin is of important practical significance for the exploration and development of the Qinghai oilfield.