Water Invasion Law and Water Invasion Risk Identification Method for Deep Sea Bottom-Water Gas Reservoir

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.

Production Allocation Optimization of Gas Reservoirs with Edge and Bottom Aquifer Based on a Parallel-Structured Genetic Algorithm

“…Natural gas has gradually become an important component of China’s energy industry. Currently, most gas reservoirs that have been developed in the world are accompanied by the development of edge and bottom water. − As production time increases, the subsequent decrease of gas reservoir pressure and irregular invasion of edge and bottom water lead to a rapid decrease in gas well productivity. , This has caused a risk of water invasion in bottom-water gas reservoirs, making gas well allocation more difficult. − In addition, the existing allocation methods have weak theoretical foundations and poor generalizability. − The decision on future energy investment requires an outlook on future energy consumption. Under and overestimation of energy consumption could lead to economic and environmental problems .…”

“… 2 − 4 As production time increases, the subsequent decrease of gas reservoir pressure and irregular invasion of edge and bottom water lead to a rapid decrease in gas well productivity. 5 , 6 This has caused a risk of water invasion in bottom-water gas reservoirs, making gas well allocation more difficult. 7 − 9 In addition, the existing allocation methods have weak theoretical foundations and poor generalizability.…”