乐东气田非烃类气层的测井识别

莺歌海盆地的乐东气田储层埋深较浅，主要目的层是第四系乐东组，埋深在950～1 300 ｍ。该气藏的气体组分除了以甲烷为主的烃类气外，还存在大量的二氧化碳等非烃类气体。如何区分烃类气体和二氧化碳气体并对它们的含量作出评估，这对天然气的测井评价工作提出了新的挑战。为此，从测井资料入手，首先识别烃类气和非烃类气储层，再根据研究区内烃类气储层与非烃类气储层在测井响应特征上的差异，利用交会图技术将这些差异体现出来，可以定性判断烃类气层与二氧化碳气层；同时，运用地层组分分析模型和最优化理论，使用多条件约束来计算烃类气体和非烃类气体的相对含量，从而达到定量识别气层类型的目的，以指导油气田的勘探开发作业。实际应用结果表明，参加检验的天然气储层中，79%的层计算烃类气相对含量与实测结果绝对误差在20%以内，证明所确定的非烃类气层常规测井定量解释方法在该区应用效果良好。

Logging identification of non hydrocarbon gas zones in the Ledong Gas Field,Yinggehai Basin

The reservoirs in the Ledong Gas Field, Yinggehai Basin, are buried shallow, the major pay zone of which is the Quaternary Ledong Formation with a burial depth of 950 – 1300 m. Apart from methane dominated hydrocarbon gases, gas reservoirs there also contain a great volume of non hydrocarbon gases like CO₂. How to differentiate between hydrocarbon gases and CO₂ and determine their content is a new challenge to the logging evaluation in this study area. Therefore, on the basis of the logging data, we first identified hydrocarbon and non hydrocarbon gas zones; then adopted the cross plot to present their difference reflected from the logging response. Thus, we were able to quantitatively judge if it is a hydrocarbon or CO₂ gas zone. Meanwhile, we adopted the formation ingredient analysis model and the optimization theory to calculate the relative content of hydrocarbon and non hydrocarbon gases under multiple constraint conditions. In this way, we can quantitatively identify the gas zone types, which will be a guidance for the exploration and exploitation operations in oil and gas fields. The actual field practices demonstrated that among 79% of the examined gas zones, the absolute error between the calculated relative content of hydrocarbon gases and the actual measurement was within 20%, which proved that this proposed method in this study is perfect.