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将声波、中子 -孔隙度、密度等三种测井手段相结合 ,可得到速度差异(Velocity -deviationlog)。该法可获得井下碳酸盐岩主要孔隙类型信息 ,并可用于预测井下成岩作用的分布特征。实验室测定 30 0多个分散的碳酸盐岩样品 ,揭示声波速度不仅是总孔隙度的函数 ,而且还是主要孔隙类型的函数。一般来说 ,孔隙度与速度呈负相关关系 ,但对于一定的孔隙类型 ,可偏离这种关系。在相同的总孔隙度条件下 ,颗粒内孔隙类型 ,如铸模孔或体腔孔 ,比粒间孔或微孔隙具有更高的声波速度。实验室测量的结果可用于标准测井资料的解释。首先利用时间平均方程 ,将孔隙度测井转换成合成速度测井 ,然后用实测声波测井与理论速度测井之间的差异作图 ,就可得到速度差异测井值。因为速度差异是在一定孔隙度条件下声波速度变化的结果 ,所以速度差异测井反映了不同孔隙类型的岩石物理特征。正速度差异标志了实测速度比理论速度较高 ,主要形成格架孔隙发育带。没有速度差异 (0差异 )表明了岩石缺乏刚性格架 ,如具有高粒间孔和微孔隙的碳酸盐岩。负速度差异表明声波速度降低 ,这可能是由井壁不规则、裂缝和含天然气引起的。通过连续追踪井下速度差异 ,可识别具有不同孔隙类型的成岩带
Combining three logging tools, such as acoustic wave, neutron-porosity, and density, a velocity difference (Velocity-deviation log) can be obtained. The method can obtain the information of the main pore types of downhole carbonate rocks and can be used to predict the distribution characteristics of downhole diagenesis. Laboratory tests of more than 300 dispersed carbonate samples revealed that sonic velocity is not only a function of total porosity but also a function of the dominant pore type. In general, porosity and velocity are negatively correlated, but for some pore types this relationship can be deviated. Under the same total porosity conditions, the intragranular pore types, such as the mold holes or body cavity holes, have a higher acoustic velocity than the intergranular or microporosity. Laboratory measurements can be used to interpret standard log data. First, the log of velocity differences can be obtained by converting the porosity log to a composite velocity log using a time-averaged equation and then plotting the difference between the actual sonic log and the theoretical speed log. Because velocity differences are the result of changes in acoustic velocity at a certain porosity, velocity-difference logging reflects petrophysical characteristics of different pore types. The positive velocity difference marks the fact that the measured velocity is higher than the theoretical one, mainly forming the framework pore development zone. No speed difference (0 difference) indicates that the rock lacks a rigid framework such as carbonate rocks with high intergranular and microporosity. The difference in negative velocities indicates a decrease in sonic velocity, which may be caused by irregularities in the borehole wall, cracks and natural gas. By continuously tracking downhole velocity differences, diagenetic zones with different pore types can be identified