Using The Equilibrium Curve Concept to Determine the Most Efficient Gas Lift Injection Pressure and Rate for A Well

The capability of a gas lift system is heavily dependent upon the available gas lift injection pressure. Gas lifting a well from the deepest point of the formation results in higher drawdown pressure, more production with less lift gas, and less gas lift equipment yielding a more efficient system. However this cannot always be achieved because of limited injection pressure, limited gas injection rate and/or limitations of the gas lift equipment. In a gas lift project, what size compressor is needed to deliver the desired production? If a compressor is already in place, how deep can gas be injected and will it achieve the desired production? To answer these questions, an Equilibrium Curve can be developed. NODAL analysis and production information are necessary to build an Equilibrium Curve for a well. The outcome of this process is a plot of liquid production rate at various gas injection depths. This will provide the necessary information to size the compression needed to achieve the target liquid production rate and to determine the gas lift mandrel and valve design. Couple this curve with additional analysis will result in liquid production rates at various gas lift injection rates. Injection rate and pressure can then be used to determine compression horsepower required. The most efficient operation will be the gas injection pressure that yields the lowest compressor horsepower per barrel of liquid produced.