吉木萨尔凹陷芦草沟组储集层脆性特征

Brittle Characteristics of Lucaogou Formation Reservoir in Jimsar Sag,Junggar Basin

吉木萨尔凹陷芦草沟组储集层岩性复杂,岩石脆性对产能影响显著。在矿物学、力学参数及能量演化特征分析的基础上,应用层次分析法,提出适合芦草沟组储集层的脆性评价新方法,对比不同岩性的脆性特征。结果表明:吉木萨尔凹陷芦草沟组储集层黏土矿物含量较少,脆性矿物各成分含量接近,矿物成分脆性指数难以准确评价其脆性;储集层非均质性强,不同岩性脆性差异较大,泥质粉砂岩、砂屑白云岩和泥页岩的综合脆性指数较大,均大于0.60;白云质粉砂岩和泥晶白云岩的综合脆性指数中等,为0.50~0.60;白云质泥岩的综合脆性指数较小,为0.49;取自同一块岩心的岩样,平行层理方向脆性大于垂直层理方向;层理发育易导致岩石破裂形态复杂,影响脆性评价结果。

The lithology of the Lucaogou formation reservoirs in Jimsar sag is complex,and the rock brittleness has a significant impact on productivity.Based on the analysis of mineralogy,mechanical parameters and energy evolution characteristics,a new method for brittleness evaluation suitable for the Lucaogou formation reservoirs was proposed,which follows an analytic hierarchy process to compare the brittleness characteristics of different lithologies.The results show that the Lucaogou formation reservoir in the Jimsar sag has a low clay content and small differences in the contents of brittle minerals,so it is difficult to accurately evaluate the rock brittleness with the brittleness index;the reservoir is very heterogeneous,and the brittleness of different rocks varies greatly:the average comprehensive brittleness index of the argillaceous siltstone,sandy dolomite and mud shale is higher than 0.60,the average comprehensive brittleness index of the dolomitic siltstone and micrite dolomite is medium,ranging from 0.50 to 0.60,and the average comprehensive brittleness index of the dolomitic mudstone is relatively lower,only 0.49;for the rock samples taken from the same core,the brittleness in parallel bedding direction is larger than that in vertical bedding direction;and the development of beddings may easily lead to complex fracture patterns,which affects the brittleness evaluation results.