Continuous gas lift optimization using genetic algorithm

Gas lift is one of a number of processes used to artificially lift oil or water from wells where there is insufficient reservoir pressures to produce the well. The process involves injecting gas through the tubing-casing annulus. Injected gas aerates the fluid to reduce its density; the formation pressure is then able to lift the oil column and forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment. Being somehow an ancient tool with an age of over a century, gas lift is though still a challenging problem when overall optimization is the concern. When the injection gas is of a limited supply the problem is finding the best gas allocation scheme. However there are increasingly emerging cases in certain geographic localities where the gas supplies are usually unlimited. The optimization problem then totally travels to the wellbore and completion string and fully engages with multiphase flow concepts. In the present study an intelligent genetic algorithm has been developed to simultaneously optimize all effective factors namely, gas injection rate, injection depth and tubing diameter towards the maximum oil production rate with the water cut and injection pressure as the restrictions. The computations and real field data are mutually compared.