利用测井视孔隙度差异识别二氧化碳和烃类气

当孔隙型砂岩储层含气时，使用测井曲线计算的视孔隙度与地层的真孔隙度、含气饱和度以及所含气的组份有关。若地层的真孔隙度和含气饱和度已知，根据中子测井视孔隙度、密度测井视孔隙度之间的差值的高低可区分气体的组份是二氧化碳气还是烃类气。给出视孔隙度差值的计算方法，并使用该方法计算出了在一定含气饱和度、不同的孔隙度的条件下，地层中分别存在二氧化碳和烃类气的理论值。在气井的解释过程中，将实际测量的视孔隙度差值与理论值相对比，看测量值接近那种类型气体的理论值，地层中就含有那种气体。当一口井的不同层位同时存在二氧化碳气和烃类气时，使用该方法来确定气体的类型，效果较好。

Using Different Logging Apparent Porosities to Distinguish Carbon Dioxide from Methane

When there exists porous sandstone reservoir, apparent porosity calculated by logs has relation with the true formation porosity, gas-bearing saturation and components of the gas. If the true porosity and gas-bearing saturation are given, carbon dioxide or hydrocarbon in the gas components might be determined form differences between neutron log apparent porosity and density log apparent porosity. A calculation method for apparent porosity difference is proposed. By using this method, theoretic values of carbon dioxide and hydrocarbon in formation are obtained when a certain gas and formation with different porosities exist. In interpretation of gas wells, the measured apparent porosity approxiate to the theoretic porosity of a certain gas indicates that such a gas exists in the formation. When there are both carbon dioxide and hydrocarbon in the different intervals in one well, it is better to use this method to determine the gas types.