准噶尔盆地西北缘克百地区二叠系风城组砂砾岩储层特征及主控因素分析

Characteristics and Main Controlling Factors of Sand-Gravel Stone Reservoir of Permian Fengcheng Formation in Kebai Area,Northwest Junggar Basin

基于准噶尔盆地西北缘克百地区30余口井的岩心、录井及测井数据,运用显微镜、扫描电镜等分析手段,通过对砂砾岩储层的岩石学、沉积学进行分析,认为准噶尔盆地西北缘克百地区二叠系风城组砂砾岩以岩屑砂岩和长石岩屑砂岩为主,沉积相以扇三角洲相和冲积扇相为主,其中以扇三角洲前缘亚相水下分流河道微相储层物性最好,可提供最有利的油气储集空间,扇三角洲平原亚相分流河道微相储层物性次之,亦可作为储层的有利区域。经过对研究区成岩机理研究认为,影响研究区砂砾岩储层的主要成岩作用为压实作用、胶结作用和溶解作用。压实作用为破坏性的成岩作用,使该区砂砾岩储层的孔隙度和渗透率减少,4 000m以深孔隙度小于10%、渗透率低于0.1×10-3μm2;胶结作用具有正反2个方面的成岩作用,既可通过胶结减少岩石的孔隙,又可通过抑制压实作用的进一步进行从而保持颗粒间的距离;溶解作用为建设性的成岩作用,尤其是深部储层中具有强烈的压实压溶作用,使油气的储集和运移变的更加有利。

On the basis of core and log data from more than 30 wells in Kebai area of northwest Junggar basin,this paper analyses the lithology and sedimentology of sand-gravel in Kebai area by means of microscope and scanning electronic microscope.Results show that the sand-gravel of Permian Fengcheng Formation in the study area mainly consists of lithic sandstone and feldspar lithic sandstone,and the sedimentary facies are dominated by fan delta and alluvial fan.The fan delta frontier subfacie underwater distributary channel microfacie with the best petrophysical property can provide favorable reservoir space,followed by the fan delta plain subfacie underwater distributary channel microfacie.Diageneses in study area mainly comprise compaction,cementation and dissolution.Compaction is destructive to porosity and permeability,which are less than 10% and 1×10-3μm2 under 4 000m.Cementation,not only destructive but also constructive,can inhibit the compaction to keep the distance among particles.The space dissolved can form channel for hydrocarbon accumulation and migration.Dissolution,especially in deep reservoir with a strong pressure,makes the migration easy.