| This paper discusses the gas-water distribution characteristics and the early identification of water invasion of
Changxing Formation gas reservoir in Yuanba, Sichuan Basin, and provides a practical method for stabilizing the gas
production. By dynamically tracking the fluid variation characteristics of gas wells and combined with static geological
characteristics, the characteristics and the controlling factors of gas-water distribution in gas reservoirs are defined. On
this basis, according to the water output type of water-producing gas wells, the early water invasion recognition model is
established. The results show that: The condensate water coexists with formation water in the produced liquid of gas well,
and the total salinity has an exponential positive correlation with daily water production and daily gas-water ratio. Free
gas and dissolved gas coexist. With the increase of water invasion degree, the content of CH4 decreases and the content of
H2S increases. No. 3 and No. 4 reef belts are dominated by free gas, and the palaeo-oil reservoirs should be located here
or in a smaller range. No. 1 and No. 2 reef belts and reef-shoal superimposed belt are gas-water transitional belts, and the
local structure and reservoir heterogeneity adjust the gas-water distribution. The development degree of fractures controls
the water production rate of gas wells, and the increase of water production is related to the gradual breakthrough of
multiple fractures to communicate with surrounding water bodies. The reservoir fractures of Changxing Formation in
Yuanba are underdeveloped, and the water production type of gas well is mainly linear, and there is a warning period of
water invasion. For gas wells with developed fractures and multi-power type of water production, it is necessary to
strengthen monitoring, and carry out rational production allocation analysis, so as to extend the time of water-free gas
production. Reef-shoal development areas in high parts of structure or in relative low parts of structure with underdeveloped
fractures are the preferred targets for deployment. The established early identification model of water invasion can be
popularized and applied. |
