| In the evaluation of deep-ultra deep oil and gas preservation conditions, not only the physical loss of natural
gas should be paid attention, but also the chemical loss of hydrocarbons under high temperature and high pressure should
be. Thermochemical sulfate reduction (TSR) is common in gypsum-bearing carbonate systems. The stronger the TSR, the
more the loss of hydrocarbons. Hydrocarbon content and drying coefficient, non-hydrocarbon content, acid gas index and
carbon / sulfur isotope series indexes can reflect TSR strength to some extent, but it is difficult to meet the needs of
quantitative evaluation. Based on the basic geological fact that all gas reservoirs with high H2S content or strong TSR in
Sichuan Basin are normal pressure gas reservoirs, while the adjacent gas reservoirs with low H2S content and not subjected
to TSR are generally overpressure gas reservoirs, it is considered that the chemical loss of TSR hydrocarbon plays a key
role in the process of overpressure gas reservoir to normal pressure gas reservoir. Therefore, using the state parameters of
natural gas under formation conditions, this paper attempts to establish a quantitative evaluation method of TSR
hydrocarbon chemical loss: ZnPVT state parameter evaluation method. Taking representative wells in Puguang, Yuanba,
Jiannan, and Weiyuan gas fields as examples, the degree of TSR hydrocarbon loss is evaluated. The results show that the
TSR hydrocarbon losses of Changxing Formation-Feixianguan Formation gas reservoir in Puguang gas field, Changxing
Formation gas reservoir in Yuanba gas field, Changxing Formation-Feixianguan formation gas reservoir in Jiannan gas
field, and Dengying Formation gas reservoir in Weiyuan gas field are 18%, 20%, 10%, and 64% of the original reserves
respectively. The evaluation result is consistent with the actual geological conditions. |
