Numerical simulation of water invasion in complex bottom-water gas reservoirs and its application:A case study of Changxing gas reservoir in Yuanba Gas Field
The gas reservoir in Changxing Formation of Yuanba area is a banded bottom-water gas reef reservoir with local interlayers.The two-phase flow mechanism is complicated for different gas-water distribution modes,leading to an incomplete understanding of water invasion dynamics.As a result,the water control measures of gas wells lack theoretical guidance,which seriously threatens the high and stable production of gas reservoirs.Based on the microscopic fluid flow experiment,the water invasion mechanisms were analyzed for different gas-water distribution modes.Early-warning models for water intrusion were established in gas wells with or without interlayers,and the risk rating of water breakthrough was carried out to put forward technical measures for differential water control and stable gas production of gas wells.The research results showed that:1)The developed interlayers in gas reservoirs make the mechanism of water invasion show significant differences.Considering the complex gas-water distribution modes can effectively improve the dynamic simulation accuracy of water invasion,and the prediction error of water breakthrough time of gas well can be less than 10％;2)For two gas-water distribution modes with or without interlayers,the influence of controllable factors from strong to weak is avoidance height,production pressure difference and wellbore diameter during the water-free production period of gas wells;3)For gas wells without interlayers,the influence of avoidance height is significantly different from the production pressure difference and inner wellbore diameter during water-free gas production periods,and the influence scale can reach more than three times that of the other two factors.The sensitivity of each factor is lower than that of gas wells without interlayers during water-free gas production periods of gas wells with interlayers,and the variation trend of influence degree tends to be consistent;4)The critical production and productivity of bottom water coning should be considered comprehensively to dynamically regulate the production pressure difference and delay the water invasion rate after identifying the characteristics of water-invaded gas wells.The average water-free gas production periods of water producing risk wells in Yuanba gas field can be extended by 2.3 years,and the water invasion control effect is remarkable.The research results effectively support the dynamic analysis of water breakthrough in Yuanba gas field and could provide technical reference for the efficient development of similar gas reservoirs.
Yuanba gas fieldbottom-water gas reservoirinterlayerdynamic simulation of water invasionwater control strategy
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