柴西地区第三纪叠层石岩石学特点与油气储集特征

柴达木盆地西部干柴沟一带发现大量第三纪湖相叠层石，主要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。根据国际上叠层石研究的最新成果和研究趋势，柴西地区叠层石可以分为丘状、柱状、指状和多边形叠层石，探讨了其中的内部构造和成分，提出不同类型叠层石所对应的生成环境。在野外露头剖面观察、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像分析等手段，详细研究了叠层石储集特征，认为不同类型叠层石所对应的孔隙类型差异很大，粒内孔隙和溶孔最为发育，原生孔隙较少，次生孔隙发育，是油气的优良储集层。柴西地区生物礁储集层的测井和地震响应良好，根据生物礁的形成特点，可以较为科学地预测生物礁的展布和发育状况。图6参18

Reservoir and lithology of Tertiary stromatolites in the West Qaidam Basin, Northwest China

Stromatolites are found to be abundant in the thousand-meter-thick lower member of the Ganchaigou Formation and the lower Youshashan Formation in the Ganchaigou area, west Qaidam Basin. The stromatolites range in morpholog from domical, columnar, digitate, to polygonal types. The observations based on outcrops, thin sections and casting sections of the stromatolites, using various analytical techniques including analysis of capillary pressure curve and pattern analysis of pore structures, suggest that the stromatolites are of different pore structure closely related to the typical form, and the intraparticle pores and dissolution cavities are best developed, with low primary porosity but high secondary porosity, favoring the formation of hydrocarbon reservoirs. The reef reservoirs have distinct log and seismic signatures, which help predict the distribution and development of the stromatolites reefs in the Qaidam Basin.