基于小井距检查井的夹层分布特征及对剩余油分布的控制作用——以萨尔图油田北二西区为例

Study on distribution characteristics of intra-formational bed based on dense inspection wells group-a case of Beierxi district of Sartu oilfield

特高含水后期,河道砂体内部夹层是影响层内剩余油分布的重要因素。针对特高含水后期密井网条件下不同类型的河道砂体,以萨尔图油田北二西区5口小井距密闭取心检查井为研究对象,采用统计和预测分析方法,对曲流河河道、辫状河河道、高弯曲分流河道、低弯曲分流河道和水下分流河道砂体内部夹层进行了定量描述,对夹层的岩性、厚度、分布部位及稳定性等特征进行了研究。结果表明,辫状河河道—曲流河河道—高弯曲分流河道—低弯曲分流河道—水下分流河道砂体内部夹层的岩性呈泥砾岩—粉砂质泥岩—泥质粉砂岩—泥岩的变化趋势,夹层厚度呈明显变薄趋势;不同类型河道砂体内部夹层厚度较小,厚度小于5 cm的夹层占总夹层数的65.5%;夹层的分布部位和倾角差异大,层内薄夹层多,测井资料无法识别的夹层占总夹层数的69.6%;辫状河河道砂体内部夹层的稳定性较好,曲流河河道砂体内部夹层稳定性最差。辫状河河道砂体剩余油主要受沉积韵律影响,曲流河河道砂体中的剩余油主要受侧积夹层控制,低弯曲分流河道发育水平稳定层理,削弱了油层内部流体因重力作用而导致的水淹程度差异,砂体内部水淹程度相对均匀,有利于驱油效率的提高。

The Daqing oilfield has entered an extra high water-cut stage.In response to the production situations of sand bodies at late high water-cut stage under dense pattern condition in Daqing oilfield,and based on five core drilling observation wells with close spacing in Beierxi for major research object,the key technology was applied in quantitative characterization of intra-formational bed of channel sandbody on the basis of development demand and technical bottleneck of current intra-formational potential finding.The study defines some essential characteristics of core size heterogeneity,the main contents of which are intra-formational bed of the typical channel sand body.Different types of channel sand body internal sandwich lithology,thickness,sandwich distribution site,dip angle and residual oil distribution are different obviously.The proportion of inter-beds unidentified by logging to total inter-beds is 69.6%. The braided fluvial channel sediments of intra-formational bed in the stability of the sandwich are good,and the meandering channel is the worst.The study of distribution characteristics of intra-formational bed provides a reliable geological basis for releasing the internal remaining oil out of fluvial channel.