构造电阻率差比值法识别火山岩裂缝地层天然气层

在基岩电阻率较高的硬地层中,除去泥质、孔隙和其他矿物等因素的影响后,地层电阻率与致密围岩电阻率的差异就被认为是裂缝以及地层孔隙中储存的流体性质引起的。选择相同岩性含气储层与致密围岩层的电阻率值,利用数值反演的方法确定出计算含气层段消除裂缝以及孔隙中流体性质影响以后的地层真电阻率公式,定义地层真电阻率和深侧向电阻率的差值与地层深侧向电阻率的比值为构造电阻率差比值,该参数主要反映裂缝以及孔隙中的流体性质对电阻率降低幅度的影响。因此,利用差比值法可以识别火山岩裂缝地层的流体性质,进而制作油层、气层和水层的判别图版,并结合其他测井曲线、油藏动态资料以及气测信息综合识别火山岩裂缝地层天然气层。该方法在准噶尔盆地研究区火山岩天然气层的识别中取得了很好的应用效果,解释结论与试油结果基本吻合。

Identification of Natural Gas Layers of Fractured Volcanic Formation by Constructural Resistivity Difference-Ratio

For the hard formation of high matrix resistivity the difference between formation resistivity and tight surrounding rock resistivity are caused by reservoir fractures and fluid property in the pore space when the factors such as mudstone,pore and other conductive minerals are eliminated.Based on volcanic lithology identification,the resistivity of gas-bearing reservoir and tight surrounding layer with the same lithology were used to determine the formation true resistivity formula of gas-bearing intervals that eliminate the factors of reservoir factures and fluid property in the pore space by use of numerical inversion method.Then the difference-ratio value of structural resistivity was defined as the ratio difference of formation true resistivity and deep investigation laterolog resistivity to deep investigation laterolog resistivity,and this parameter mainly reflect the influence of the reduced rate of resistivity due to reservoir fractures and fluid property in the pore space.This method can identify fluid property of volcanic fractured formation,and form the identification plate of oil layer,gas layer and water layer for volcanic reservoir.Combined with other well logging curves,reservoir performance data and gas surveying information,it can effectively evaluate and identify the natural gas layers of volcanic fractured formation.This method has been applied to volcanic natural gas layer identification in the Junggar basin research area and has got good application effect,the interpretation conclusions and oil testing results are basically consistent.