A case study modelling pipeline layout and asset-wide choke optimization in a dry gas field of multiple reservoirs is presented. The methodology utilized an integrated asset model (IAM) and lexicographic optimizer with a neural network accelerator to perform production optimization while considering system constraints on the quality of the produced gas blend as well as the effect of significant differences in reservoir pressure on total asset production. The field comprises several gas reservoirs; some are already developed and in production, and others are in development with more wells to be drilled and brought online later. Production from the different reservoir units is commingled as the units tie into a common surface production network. Based on preliminary simulation studies, the commingled pipeline causes production deferment due to backpressure. It was postulated that a dedicated, high-pressure pipeline would be required to mitigate this. The purpose of this study was to investigate if the cost of the dedicated pipeline could be avoided by selectively choking back high-pressure wells to allow lower-pressure wells to flow and assess the incremental recoverable volume is CO2 content in blended gas was optimized.
The first step of the pilot study was to create a representative surface network model that could be coupled to the available subsurface black oil simulation model for two of the fields. A model integration software platform was used for linking the surface to subsurface, and a representative simulation control strategy was input. A custom-built choke optimization logic using an optimizer that honors the CO2 constraints and maximizes gas production up to the asset sales gas plateau target was implemented and triggered every month during the simulation. The optimized simulation generates a gas rate and choke pressure drop schedule per month per well that then can be used to develop a monthly choke set-point schedule. The simulations were run for 12 years.
Based on the results, using choke optimization, the production deferment—cumulative production difference between dedicated pipeline and comingled pipeline—can be reduced by up to 80%, making the choke-optimized comingled pipeline case more economic than the equivalent dedicated pipeline case. In addition, cumulative production can be increased by approximately 34% in both dedicated and comingled pipelines while honoring the CO2 production constraint.
The results of this study demonstrate the potential benefits of choke optimization in the gas field to both increase production by better field management and offset the need for an expensive dedicated pipeline, allowing the field improve its production potential at minimal cost.