Abstract
This study analyzes the water invasion characteristics and water encroachment of the deep sea bottom-water gas reservoir (LS17 field) in the South China Sea for the purpose of developing horizontal wells. Gas-producing profile tests and a three-dimensional (3D) water invasion simulation are used to produce a quantitative analysis of the bottom-water cresting influence factors. On this basis, we establish a suitable risk identification method for the water influx of a deep bottom-water reservoir. The results show that: (1) During the development of a bottom-water gas reservoir, the water ridging is affected by reservoir heterogeneity, production system and heel–toe effect of a horizontal wellbore, and reservoir heterogeneity is the main influencing factor; (2) the horizontal–vertical ratio of the well area determines whether the gas well productivity will be affected by the risk of water invasion. The stronger the reservoir heterogeneity, the smaller the safety limit value of the horizontal–vertical ratio; (3) when the permeability differential increases gradually, the safety limit value of the transverse longitudinal ratio decreases in turn; (4) based on the relationship curve between permeability level difference and the safety limit value of the horizontal–vertical ratio in the well area, the horizontal–vertical ratio of the N1H well is far greater than the safety limit value. The well is at high risk of water invasion and should be developed by water control. In order to improve deep seabed water and gas reservoirs, water control development should be carried out in well areas with sufficient water energy and high water invasion risk. The water invasion characteristics of bottom-water gas reservoirs under different water control technologies (such as variable density screen technology, filling water blocking, breathable coated gravel technology, etc.) and production systems (periodic gas production technology) should be studied. The research results can not only judge the water invasion risk of deep seabed water and gas reservoirs under different permeability levels and gas production rates but also provide a reference for water control development of offshore and onshore bottom-water and gas reservoirs.
Highlights
Because water invasion will reduce the recovery efficiency of water gas reservoirs, it is of great significance to clarify the water invasion mechanism and put forward an effective water invasion risk identification method for the efficient development of water gas reservoirs
When the horizontal and vertical ratio of the well area is 60 (WS-4), the water flowing into the bottom ridge significantly shorted the stable production period of the gas well, and the recovery rate of the gas reservoir decreased to 87.68%
It can be seen that the horizontal/vertical ratio of the well area determines whether the gas well productivity is affected by water invasion, and the heterogeneity of the reservoir will affect the identification limit of the water invasion risk
Summary
Because water invasion will reduce the recovery efficiency of water gas reservoirs, it is of great significance to clarify the water invasion mechanism and put forward an effective water invasion risk identification method for the efficient development of water gas reservoirs. Liu Huaxun et al [8] believed that the stronger the reservoir heterogeneity was, the faster the formation water advanced and the earlier the water appeared in the gas well. Scholars have studied the identification methods of water invasion in gas reservoirs with water. Deng Chenggang et al [10] believed that the apparent geological reserve method could be used to discover the characteristics of water invasion in pore type and relatively homogeneous weak water drive gas reservoirs earlier. Li Yong et al [11] proposed a water-penetration risk assessment method for water drive gas reservoirs
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