Cause analysis of natural gas with high water saturation and low gas saturation in high-temperature and high-pressure zone of DF area in Yinggehai Basin

Key words:  condensate water  gas saturation  low permeability reservoir  high temperature and high pressure  Yinggehai Basin

Abstract:

The water content in the coexisting gas phase was measured under high temperature and high pressure, using an ultra-high pressure fluid PVT system. Using the micropore membrane technique, the maximum gas saturation of samples with different physical properties was measured. Based on the experimental results, and combined with the study of the actual geological data, the source of water and the cause of gas reservoirs with high water saturation and low gas saturation are analyzed in the high-temperature and high-pressure zone of DF area, Yinggehai Basin. The results show that there is a positive correlation between water content in the coexisting gas phase and temperature, and a negative correlation between water content and pressure. The water content is not very high at the highest temperature of 180 ℃ and the highest pressure of 130 MPa in this experiment, with its mole fraction only accounting for 1.51% of the whole gas phase system. The condensate water content in the gas reservoir is not very high at high temperature and pressure. The output water of gas reservoirs is mainly from pore water in the layers, and the condensate water is not the main source. The gas saturation of gas reservoirs are mainly controlled by the physical property of the reservoir and the impermeable interlayers. When the physical property becomes poor, its maximum gas saturation will reduce rapidly. In addition, impermeable or poor permeable interlayers will also lead to the reduction of the gas saturation in the gas reservoir. Therefore, low permeability reservoirs and the occurrence of interlayers should be the main causes of gas reservoirs with high water saturation and low gas saturation in the high-temperature and high-pressure zone of DF area, Yinggehai Basin, rather than the high condensate water content.