Optimization of Gas Lift Throughout the Well Lifecycle in Unconventional Reservoirs

Abstract

Given the pronounced nature of production decline in shale reservoirs, an integrated reservoir-well model that can efficiently anticipate the changes in reservoir and lift parameters over time is required in order to maintain optimum performance. The solution presented in this paper uses a novel integrated reservoir-well model specifically tailored for unconventional reservoirs to calculate the system deliverability and optimize gas injection throughout the well life. The integrated model is deployed in the cloud. It enables automation of the above process and allows more valuable exploitation of oilfied sensors such as multiphase flowmeters and of process control equipment in digital oilfields. The model calculates for each well, the oil rate versus gas injection rate at any time during the well lifecycle by simultaneous solution of the reservoir transient IPR and the wellbore model. The resulting gas demand displays the typical maximum oil production and corresponding maximum gas injection rate beyond which oil rates would decline. The derivative is then used to calculate the gas injection rates versus time that meet a specific predefined economic objective. Single-well and multi-well scenarios are investigated and the impact of gas supply limit is evaluated to illustrate the practical applicability of the solution. Examples illustrate how the gas allocation among the different wells is calculated to achieve the optimum impact. Comparison of the production when gas injection supply is unrestricted versus production results with restricted gas supply is made and results of staggered production are presented.