(248f) An Optimal Production/Injection Scheduling for Gas Condensate Reservoirs with Gas Recycling

The recycling process is a common industrial technique to improve condensate production from natural gas condensate reservoirs. The life cycle net present value (NPV) is an economic measure involving both time and cost, to evaluate the recycling process with respect to the injection and production costs.

This work highlights necessary elements and workflow for recycling design prior to implementation for improved production strategy. We will present an operational schedule for gas recycling using model-based stochastic optimization. Since life-cycle model-based optimization of a gas condensate reservoir is a time-consuming and CPU intensive task, this work suggests optimizing the process using the full compositional model of the reservoir and a simplified compositional interacting-tanks (CIT) model for calculation of objective function. In this approach, the reservoir grids are divided into two large columns of grid blocks (tanks). One of these columns contains a group of producing wells, and in the other column, the produced dry gas from the separator is recycled back into the reservoir. CIT increases the simulation speed as well as optimization in the early iterations.

After a careful analysis of three different evolutionary algorithms, a hybrid particle swarm optimization and genetic algorithm (PSO-GA) is used to maximize life-cycle NPV. To ensure applicability of the proposed method regarding the speed of optimization process and accuracy of the results, the scheduling technique is evaluated with a benchmarking synthetic model from the literature. PSO-GA optimization combined with the full/CIT model provides accurate results compared with the optimization using the full model while increasing the speed and efficiency of the optimization process. In addition, the proposed technique is used to develop a production plan for a field sector. The optimized schedule considerably increases the NPV of the recycling process.

Since there is a difference in the price of injected gas in cold and warm seasons, the optimized reinjected gas in the cold season is about half of the gas in the warm season. This study also shows the sensitivity of the optimized gas-recycling scenario to the richness of gas condensate reservoirs.