The manner of estimating water drive gas reservoir recovery can vary considerably. Several mathematical models have been developed for estimating water influx in petroleum industry, but the current paper will address the application of Fetkovich aquifer model to predict the gas reservoir performance considering the pressure changes that gradually occur within the aquifer and between the aquifer and reservoir. The applicability of this model has proven to be extremely useful in estimation of initial gas resources, aquifer volume and its parameters, confirming the producing mechanism but also forecasting the production performance of the gas reservoir. The authors will highlight through some case studies, the importance of the water influx analysis and prediction, in particular for natural gas reservoirs, which subsequently allows for adequate planning in optimizing the reserves' recovery.

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A frequent challenge encountered in the exploitation of mature gas fields located in the Getic Depression is sand production. Causes of sand production are mainly related to degree of rock consolidation, lithology, increasing water production and production rates. The effects of sand production are multiple such us low productivity of the gas wells, accumulation into the surface equipment, erosion of downhole and surface equipment, plugging the perforation zone and casing damage. The current paper will address the sand production- challenges and new perspectives in remedial work of wells which are producing from gas reservoirs located in Getic Depression. The article presents through some case studies the research performed for the implementation of the frac-pack technology in some gas wells.

Abstract. Gas mature fields are associated with challenges to optimize the hydrocarbon flow from reservoir to the sales point in a cost effective manner due to declining well productivity. Laslau Mare field is a mature gas field in Transylvanian basin (Mures County) developed in 1970s and is producing ~99% methane with low water-gas ratio. As any brown field, the state of depleted reservoir will generate several constraints for gas flow from formation to surface facilities and further to delivery point. During the exploitation has been observed that the operation conditions are facing with unstable pressure in the system due to low demand. Therefore, the back pressure effect will affect the wells in terms of inability to unload the bottomhole accumulated liquids and the reservoir will suffer a higher pressure drawdown. The best fit-for-purpose solution to overcome the above challenges is represented by installation of group compressor. Laslau Mare field has 3 group compressors running and shows positive results, especially when external pressure fluctuates continuously. This paper explain the challenges seen in 2016 in Laslau Mare field with back pressure effects and how the compression overcome them, and also other solutions that should be considered to optimize the well production.