保压取心储层流体饱和度分析方法——以柴达木盆地台南气田第四系生物成因气藏为例

An analysis method for reservoir fluid saturation by pressure coring:A case study from Quaternary biogenetic gas reservoirs in the Tainan Gas Field,Qaidam Basin

为了准确获取柴达木盆地台南气田第四系疏松泥质粉砂岩储层原始流体饱和度,在其区内两口气井中应用保压密闭取心及其配套分析技术,对储层温压条件下所含流体含量进行了测定。具体方法是,运用保压密闭取心技术保证岩心从井筒提升到地面后仍保持地层压力,冷冻截取过程中系统收集游离气和游离水,并对岩样开展束缚水、可动水及残余气饱和度等实验分析研究,依据岩心孔隙体积最终按照地面实际收集的流体体积通过校正得到地层温压条件下储层孔隙内的原始气、水总饱和度和可动流体饱和度等参数。在此基础上,对比测井解释储层流体饱和度后发现,测井求取值偏大、物性好的气层平均相差17.89%,物性中等的气层平均相差为20.79%,物性差的气层平均相差36.64%。结论认为,只有采用保压密闭取心才能够准确获取储层的真实原始流体饱和度,其对测井解释计算方法具有修正作用。

For getting the initial fluid saturation of the Quaternary argillaceous siltstone reservoirs in the Tainan Gas Field, Qaidam Basin, pressure coring and its supporting analysis technologies were adopted in two gas wells in this area to measure fluid content under the conditions of reservoir temperature and pressure. Based on pressure coring technology, the cores were kept in reservoir pressure when they were taken to the surface from the wellbore. Free gas and water were systematically collected in the process of freezing cutoff. Experiments were conducted on rock samples to investigate the saturation of bound water, movable water and residual gas. After core pore volume was ultimately corrected on the basis of actual volume of the fluid collected on the ground, the initial gas and water saturation and movable fluid saturation of reservoir pores were measured under the conditions of reservoir temperature and pressure. Then, they were compared with logging reservoir fluid saturation. It is indicated that the logging values are higher, with average difference of 17.89% for gas reservoirs with good physical properties, 20.79% for those with medium physical properties and 36.64% for those with poor physical properties. In conclusion, pressure coring technology is the only way to obtain the real initial fluid saturation of reservoirs and it is available for correcting logging interpretation calculation methods.