Thesis (M.Eng.)--Chulalongkorn University, 2007

Water production in commingled monobore gas wells has been the crucial problem for maximizing recovery of muti-stack compartmentalized gas reservoirs in Pattani basin, Gulf of Thailand. After one or more sands produce a significant amount of water, the other sands suffer from the effect of hydrostatic backpressure from the produced water because they share the same wellbore. Shutting off water-out sand(s) is the major method to resolve this problem. This study aims to improve sub-surface water management process. The main focus is on the prediction of critical velocity of gas well before it stops flowing and determination of individual zone gas reserve by building muti-tank commingled model and history match surface production and production logging data. By knowing critical gas velocity, best timing for production logging survey before well stop flowing can be planned to identify the water producing sand(s) as well as knowing OGIP of individual sand, better decision on water shut off intervention could be done with higher success ratio. It is hoped that the outcome of the study will be used as the tool to improve reserve management to maximize recovery of these marginal gas reservoirs in the Gulf of Thailand