四川盆地基性火山岩气层流体性质测井判别方法

Well-logging identifying method for the fluid properties of mafic volcanic gas reservoir in Sichuan Basin

四川盆地发育的基性火山岩储层具有电阻率低、变化幅度小,导电机理复杂的特点,利用传统的电法测井对储层流体性质判别具有较大的局限性。为此,利用阵列声波和密度测井等非电法测井建立了一套完整的储层流体性质评价方法。分析了利用岩石有效泊松比与岩石有效压缩系数判别火山岩储层流体性质的适用性,通过Gassman方程提取孔隙压缩系数,建立了岩石压缩系数与泊松比差值和孔隙压缩系数的交会图版,实现了气层与非气层的判别;分析四川盆地火山岩地层岩性、物性以及孔隙流体对拉梅系数的影响,利用与火山岩物性相关性较高的纵波时差对拉梅系数进行改进,建立了基于拉梅系数的流体性质判别图版,达到区分气层、水层和干层的目的;引入弹性模量差值法,分析了孔隙度、含气饱和度对弹性模量差值的影响,表明该方法能够提高对含气饱和度的灵敏性,同时降低孔隙度的影响。该套方法在盆内新钻火山岩探井储层流体性质综合评价中取得了良好的应用效果。

The mafic volcanic reservoirs developed in Sichuan Basin are characterized by low resistivity, small changes and complex conducting mechanism, and there are much limitation for the traditional electrical logging method to identify fluid properties. Therefore, with the help of the non-electrical well loggings such as array acoustic logging and density logging, a complete set of fluid property evaluation methods are established. First, the feasibility of rock effective Poisson’s ratio and rock effective compressibility coefficient are analyzed to distinguish the fluid properties in volcanic reservoirs, and the compressibility coefficients of the pore liquid are extracted by Gassman equation;the cross-plot chart board of fluid compressibility coefficients with the differential between rock compressibility coefficients and Poisson’s ratio is established to realize the identification between gas zone and non-gas zone. Second, the effects of lithology, physical properties and pore liquids of volcanic formation on the Lame coefficient in Sichuan Basin are analyzed. The Lame coefficient is improved by P-wave time difference which has a high correlation with the physical properties of volcanic rocks, and the identifying chart-board of fluid properties is established on the basis of Lame coefficient to distinguish gas layer, water layer and dry layer. By introducing the difference method of elastic modulus, the influences of porosity and gas saturation on the elastic modulus difference are analyzed, which shows the method can enhance the sensitivity to gas saturation and reduce the influence of porosity. This method has achieved good applied effects in the comprehensive evaluation of reservoir fluid properties for the newly drilled volcanic-rock exploring well in the basin.