Optimization of the lift gas compression system at the Eldfisk Complex

Abstract

The intention of this study was to maximize the oil production of the Eldfisk field. Two major constraints were encountered limiting the amount of gas that can be injected into the wells. Optimizing production taking these constraints into consideration will thus maximize production. A MatLab code has been developed for this work and 18 wells of the Eldfisk field have been simulated to compute the optimum gas lift injection rate. Given the limitations the economic optimum has been estimated from the gas lift performance curve of every well. The economic optimum has been calculated for the actual conditions of the field and also for a scenario with a higher water cut, corresponding to future operation. The results of the economic lift gas injection rate were used as input data for a HYSYS case, with the objective to optimize the compression system on Eldfisk 2/7 E. Three aspects of the compression system were of main concern: insufficient discharge pressure, high recirculation rates and low efficiency of the third stage of compression To optimize the compression system, different scenarios were evaluated with the objective to find the best scenario for the discovered issues. One solution was found that allowed all of the issues previously mentioned to be covered successfully simultaneously. By reducing the speed of the compressors, the discharge point for lift gas was moved from the second to the third compression stage, also the pressure for gas lift wells was increased to the specified range and the recirculation rates were decreased so the scrubbers will not be working to their limit capacity, finally with these modification the overall power consumption was reduced.