Dynamic Optimization of Water-Injection Wells Operation for Enhanced Oil Production from a Mature Oil and Gas Field

Field engineers in the oil and gas industry are constantly faced with the challenge of maintaining profitability amidst several operational constraints whose effects span through all time horizons. With the inevitably high environmental and financial stakes associated with the exploration and production of an oil and gas prospect, there is a strong incentive to enhance hydrocarbon recovery and production via systematic and mathematical-oriented approaches to obtain best possible conditions. In further response to this challenge, the application of sophisticated simulation methodologies to integratedly capture the reservoir behaviour, multiphase flows (in wellbores and flowlines) and gas-oil-water separation in the processing facilities is constantly on the increase. Liquid loading in gas wells and artificial lift design considerations, reservoir pressure maintenance via water injection, gas/water coning during production from deviated wells, pressure drop and liquid holdup of multiphase mixtures in highly deviated flowlines are some of the specific complexities associated with this system. Simulation of these prevalent subsurface and surface phenomena does not always guarantee an accurate prediction of the on-set of these problems let alone, a problem-free operation in a field. In order to tackle the insufficiencies and thus reduce the uncertainties of the current state-of-the-art models, it is necessary to also combine robust optimisation methods with these flow simulations. This combination of simulation and optimisation algorithms increases the order of complexity due to model-nonlinearity, non-convexity and the presence of discrete variables. There has been an increasing number of contributions in the application of optimisation techniques to field production, and this can be attributed to the advances in the development of specialised algorithms and accompanying computational power. To date, most of these attempts have focused on fields undergoing primary production through majorly vertical wells. We add to existing knowledge in this field by formulating a Real-Time Production Optimisation problem via simultaneous consideration of production and injection wells with both vertical and deviated geometries. A field undergoing secondary production is considered in this study. We utilise the tools of multiphase flow and reservoir simulation for the flowrate and pressure drop evaluation in wellbores and flowlines of the considered production network; extra measures are taken to ensure all flowlines are free from hydrate and wax at the prevalent temperature and pressure conditions. The problem is solved as a nonlinear program (NLP) comprising of an economic objective function and several constraints to ensure operational feasibility. The adopted optimisation technique yields a reasonable increase in oil production compared to the usual and direct application of a blackbox simulator. This also translates to an increased NPV with the current oil price; thus demonstrating the efficacy of the proposed method as a value addition tool.