Boosting Condensate Recoveries of a Mature Retrograde Gas-Condensate Field in Pakistan

Abstract One of the most challenging part of managing a Gas-Condensate reservoir is to reduce Condensate Banking and its damaging impacts on the overall recovery. Several techniques have been applied in the past to overcome this problem such as pressure maintenance by Gas Injection (i.e. Lean gas, CO2 or N2), Water-Alternating-Gas (WAG) or chemical injection etc. However, none of these techniques could easily be initiated on a mature Gas-Condensate Field owing to the large upfront CAPEX and technical limitations. This study presents a strategy on such a mature Gas condensate reservoir, to target the Condensate banks and improve the overall condensate recovery. This study has been based on a field currently producing from the Potwar basin of Pakistan. The current pressure of the field is around 2500 psi - significantly lower than the Initial Reservoir Pressure (5200 psi) and Dew point (4950 psi). The PVT reports are showing that the reservoir has already passed the region of Maximum Liquid Drop out (MLDO). Thus, there was a risk of losing a good amount of Condensate if proper measures were not taken. This study focuses on the strategy to target these Condensate banks being accumulated at different locations of the Field, which has given an increment of around 30% already in the condensate production rates. Since the reservoir pressure has already dropped considerably below the dew point pressures - conventional CO2 or Lean gas injections cannot be utilized as they require significant re-pressurization which is technically and economically impossible at this stage of field's life. In this study, an alternative approach taken, is presented which increases the overall condensate recovery by almost 90%. This includes drilling smartly placed production wells (at locations which were not very attractive in the start of field development) and the overall impact of placing the injectors for Selective Water Flood using comprehensive reservoir simulation and water flood algorithms. This paper illustrates the approach that can be utilized in a mature gas condensate field where no pressure maintenance has been performed since the start - to improve the overall condensate recovery. This paper presents a clinical analysis of targeting the Condensate banks and possible usage of selective water flood strategy to sweep these banks along with the optimum placement of wells and injectors. This offers an innovative approach towards such gas condensate fields which are facing the problems of condensate drop out and re-pressurizing the field to a higher Reservoir pressures, at current stage, is next to impossible.