气藏凝析水引起的地层水矿化度淡化问题——以四川盆地新场气田须二段气藏为例

Formation water desalination caused by condensate water of gas reservoirs:A case study of the 2^(nd) Member of Xujiahe Formation in the Xinchang Gas Field,Sichuan Basin

前人据研究成果提出了高温高压气藏地层水矿化度变化较大的认识,由此有可能得出与实际情况不一致的结论,其主要原因是忽视了低矿化度凝析水的影响。为此,利用四川盆地新场气田须家河组二段气藏投产以来获得的产出水样矿化度资料,研究了不同水气比阶段的井口水样矿化度特征,认为井口产出水样矿化度明显受到了凝析水淡化的影响,气藏井口产出水可以划分为凝析水、地层水及其两者的混合水。研究结果表明:①井口产出水矿化度随气井水气比增大而增高,由低矿化度凝析水向高矿化度地层水转变;②当气井水气比小于0.1 m^3/10~4 m^3时,井口产出水为矿化度小于1 g/L的凝析水;③当水气比为0.1~0.8 m^3/10~4 m^3时,水样矿化度介于凝析水和地层水之间,水样以混合水为主;④气井水气比大于等于0.8 m^3/10~4 m^3时,水样最接近于地层水矿化度,凝析水对水样矿化度的影响可以忽略;⑤在排除凝析水淡化影响后,单一气藏地层水矿化度差异不大,新场气田须二段气藏变化范围在93.47~120.05 g/L之间。

Based on previous data, the formation water salinity of high temperature and hlgh-pressure gas reservoirs varies in a large range, because the effect of low-salinity condensate water is neglected. In this paper, therefore, the salinity of wellhead water sam ples was analyzed for different watevgas ratios by using the salinity data of water produced from the gas reservoir of the Second Member of Xujiahe Formation, Xinehang gas field in the Sichuan Basin. It is indicated that the salinity of wellhead water samples is influenced greatly by the desalination of condensate water. The water produced from gas reservoirs is divided into condensate water, formation water and their mixture. It is shown that the produced water changes from low-salinity condensate water to high-salinity formation water because its salinity rises With water-gas ratio of gas wells. When the water-gas ratio is less than 0.1 m3/104 m3 , there is condensate water with salinity lower than 1 g/L at the wellhead. When the water-gas ratio is （0.1 - 0.8） ms/104 m3 , mixture is dominant with salinity between condensate water and formation water. When the water-gas ratio is more than 0.8 ms/104 m3 , the sample salinity is mostly controlled by formation water and the effect of condensate water on sample salinity can be ignored. After the effect of condensate water desalination is removed, formation water salinity of single gas reservoir varies little. For the gas reservoir of the Second Member of Xujiahe Formation in the Xinchang Gas Field, it is in the range of 93.47 - 120.05 g/L.