柴达木盆地乌南—绿草滩地区下油砂山组滩坝砂岩特征与储层评价

Lower oil sand hill formation beach-bar sandstone characteristics and reservoir evaluation in Wunan-Lucaotan area,Qaidam Basin

笔者运用综合地质分析手段,研究了柴达木盆地乌南—绿草滩地区下油砂山组滩坝砂岩发育分布规律、储层特征及其储集性能,分析了滩坝砂岩受古地形、古湖盆岸线形态和沉积基准面等因素控制,平面上主要分布于湖盆拐弯处辫状三角洲侧翼的潮汐环境宽缓斜坡和古隆起上,纵向上滩砂多发育在短期基准面上升半旋回,坝砂主要发育在短期基准面下降半旋回,并且具有储层薄、喉道细、渗透率低的特征。储集空间类型主要为原生粒间孔,储层储集性能取决于沉积微相类型、成岩作用和孔隙结构类型及孔喉分选性等因素。文中对研究区滩坝砂岩储层进行了评价,分为3类储层,其中Ⅰ类储层为区内的较优质储层,Ⅱ类地层为中等—偏差储层,Ⅲ类为差储层。

In this paper the authors carefully and integratedly studied the deposit and distribution,reservoir characteristics and reservoir properties of Lower oil sand hill formation beach-bar sandstone in Wunan-Lucaotan area,the conclusions were reached as the following:the deposit of the beach-bar sandstone was controlled by three factors,the paleotopography,ancient lake shoreline morphology and the deposit datum,over the exploration area the beach-bar sandstone mainly distributed on wide gentle slopes and paleo-uplifts in lake basin windings and braided delta flanks under the tidal environment,vertically beach sandstone mainly deposited in short-term datum upward half-cycles while the bar sandstone mainly deposited in short-term datum downward half-cycles with thin layer,tiny throat and low permeability as their reservoir properties.The major type of the reservoir space is native intergranular pore,the reservoir properties depend on sedimentary microfacies types,diagenesis,micro-pore structure types,pore-throat sorting and other factors.In this paper the beach-bar reservoirs in Wunan-Lucaotan area,Qaidam Basin were evaluated and were divided into 3 levels,the good reservoir,the mediocre reservoir and poor reservoir.