天然气藏中二氧化碳含量的测井定量评价方法

摘要

When carbon dioxide exists in gas zone,pore fluid composition and logging response are getting more complex because of the presence of hydrocarbon gas,non-hydrocarbon gas and irreducible water. The extra conductivity caused by the dissolution of carbon dioxide is absolutely weak and no apparent regulation exists in it,which makes qualitative identification and quantitative calculation of carbon dioxide very difficult. According to the different influence of methane and carbon dioxide on thermal neutron moderation and diffusion,this paper builds the carbon dioxide quantitative calculation model with porosity logging methods based on neutron′s long and short spacing counting rates. Then,in consideration of the logging response features of methane and carbon dioxide with reservoir at high temperature and high pressure,and by using porosity and saturation data,we adopted the optimization method based on rock′s physical volume model and calculated the content of each fluid composition. The effect is proven to be reliable through comparison between the interpretation results and testing conclusion.%当气层中含有二氧化碳时，由于烃气、非烃气以及束缚水同时存在，导致孔隙流体成分及其测井响应趋于复杂，尤其是二氧化碳溶于水后形成的附加导电性不强且无明显规律，使得运用电阻率方法对二氧化碳的定性识别和定量计算变得非常困难。基于孔隙度测井方法，利用甲烷气体和二氧化碳气体对热中子减速以及扩散方面影响的差异，选取中子长短源距计数率值建立了二氧化碳定量计算模型。同时，考虑到在储层高温高压条件下甲烷和二氧化碳气体声波和密度测井响应特征，结合已有的孔隙度和饱和度数据，运用基于体积物理模型的最优化方法对各流体成分的含量进行计算。将两种方法同试油和测试结果进行了对比，均取得了良好的效果，证实了方法的可靠性。