致密砂岩气藏渗透率定量评价新方法及应用——以东海陆架盆地西湖凹陷X气藏为例

A new method of quantitative permeability evaluation for tight sandstone gas reservoirs:An example from X gas reservoirs,Xihu Depression,East China Sea Shelf Basin

东海陆架盆地西湖凹陷X气藏发育低孔特低渗储层,由于孔隙类型多样,结构复杂,常规孔渗关系变化繁杂,传统的孔渗关系统计回归方法以及常规测井解释方法计算的储层渗透率精度较低,不能满足低孔特低渗储层渗透率评价需求。孔隙结构直接制约储层的渗流特性,岩心压汞毛细管压力实验资料能够定性区分不同孔隙结构的储层,通过计算出样品的流动单元指数(FZI),得到3种不同类型储层的流动单元指数范围,然后建立岩心流动单元指数和测井曲线之间的关系,通过KNN(K类最近邻)算法计算出未取心层段的流动单元指数值,根据分类建立不同类型储层的渗透率计算模型。研究结果表明:①压汞资料和流动单元指数两者相互验证对储层分类更加准确;②新方法计算的渗透率与岩心分析渗透率吻合较好,较常规孔渗关系计算的渗透率精度高,渗透率平均相对误差在30%以内。

In X gas reservoirs,Xihu Depression,East China Sea Shelf Basin,there are low porosity and extra low permeability reservoirs characterized by multiple pore types,complicated pore structures,and complicated changes of conventional porosity-permeability relationship.So,the accuracy of permeability calculated by traditional statistical regression method of pore-permeability relationship and conventional logging interpretation is too low to meet the demand of evaluation on these low porosity and extra low permeability reservoirs.The pore structure directly restricts the percolation characteristics of reservoirs,and many mercury-injection experimental data of core capillary pressure can be used to qualitatively distinguish these reservoirs with different pore structures.The range of flow zone index(FZI)in three different types of reservoirs was obtained.Then,the relationship between core FZI and logging curve was established.Thirdly,the FZI of uncored intervals was calculated by using the KNN algorithm.Finally,different models to calculate permeability were established for different types of reservoirs.Results show that(1)the mutual verification between mercury injection data and FZI may increase the accuracy of reservoir classification;and(2)the permeability calculated by this new method is in good agreement with one from core analysis,even more accurate than the calculation from conventional porosity-permeability relationship.Its average relative error is less than 30%.