Current practices utilize chokes in the wellhead to induce a pressure drop in high production gas wells to produce at a constant rate. Consequently, in this setup, the potential for this pressure to be made useful is lost. In contrast, the use of a turbo-expander could induce this same necessary pressure drop while simultaneously utilizing it to generate energy. To estimate the potential benefits of this modified system, some assessments were made.

All tests conducted in this investigation utilized the thermodynamic property tables of pure methane to model the performance of produced reservoir gases. The first test conducted attempted to model the amount of mechanical energy lost across a typical choke at varying pressure ratios and flow rates. The second test modelled the theoretical energy that could be harvested across a turbo-expander. Using the relationships deduced between pressure ratio and power generated across a turbo-expander an equation relating the two parameters was derived. This equation was then applied to a case study representing a high producing gas well in the Middle East region to appraise the effectiveness of turbo-expander use on wells of this caliber. Reservoir parameters were estimated based upon parameters typically found in the region and were then used to create a production forecast for one well. The results of this case study indicate that expansion use in gas wells with production rates of roughly 100 MMSCFD/well show an average power generation of 2.2 MW/D/well in a five-year span towards the middle of the plateau production region. Over an entire production plateau and at some different wells, the power generation benefits of turbo-expander use could greatly improve the energy efficiency of gas production wells.

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Mr. Mohamed Idris