柴达木盆地扎哈泉地区致密油有效烃源岩识别与预测

2013年以来,在柴达木盆地扎哈泉地区新近系上干柴沟组发现了大型致密油藏。为了评价该地区烃源岩有效性,并有效支撑井位部署,通过岩心观察、全岩分析、地球化学分析、沉积环境分析、测井响应特征对比等,建立了岩心资料标定下的有效烃源岩测井识别方法。不同于典型烃源岩,研究区烃源岩并不具备典型的测井响应特征,总有机碳含量与声波时差、自然伽马、电阻率、密度等测井参数相关性较差。分析发现总有机碳含量与钍铀比和自然伽马与去铀自然伽马之差相关性较好,并建立公式计算总有机碳含量,方法简单且效果较好。研究区烃源岩镜质体反射率为0.624%~1.265%,处于成熟阶段,利于生油。对研究区24口井有效烃源岩识别后发现,从新近系上干柴沟组Ⅳ砂组到Ⅰ砂组有效烃源岩发育区由北西逐渐向南东方向迁移,且浅湖区烃源岩与滩坝在纵向上相互叠置,形成优越的源储配置。该方法对致密油藏烃源岩评价和勘探部署具有一定的指导作用。

Identification and Prediction of Effective Source Rocks for Tight Oil in Zhahaquan Area,Qaidam Basin

Since 2013,large-scale tight oil reservoirs have been discovered in the upper Ganchaigou formation of Neogene in Zhahaquan area of Qaidam basin.In order to evaluate the availability of the source rocks in the area and to effectively support the well deployment,a core -calibrated logging method to identify effective source rocks is established on the basis of core observation,whole rock analysis,geochemical analysis,sedimentary environment analysis and log response comparison.The logging response characteristics of the source rocks in study area are not very typical,and the TOC is poorly correlated with logging parameters such as interval transit time,natural gamma ray, resistivity and density.It is found that the TOC is well correlated with the difference between total natural gamma ray and de-uranium natural gamma ray and the ratio of thorium to uranium,respectively;and then a formula is built to calculate TOC.The method is simple and effective.The vitrinite reflectance of the source rocks in study area is 0.624%~1.265%,which is in the mature stage and is conducive to oil generation.After identifying the effective source rocks of 24 wells in study area,it is found that the effective source rock development zones in the Ⅳ toⅠ sand member gradually migrate from the northwest to the southeast.Furthermore,the source rocks and the beach bar overlap each other vertically in shallow lake area,forming a good source-storage configuration.The method can be a guidance for source rock evaluation and tight oil exploration and deployment.