Network Options

The user has the flexibility to define surface conditions (temperature and default elevation) and geothermal gradient between the surface and bottomhole.

Temperature modeling options include Thermal/Isothermal for the reservoir model and Thermal above the reservoir for the surface network. Default flowline parameters and flow correlations can be set by the user and overridden for desired flowlines to honor local realities.

Network Elements

Surface network construction is done interactively by locating and connecting elements in an aerial map using mouse clicks. Network elements (such as separators, compressors, joints, pumps, sources/sinks and wellheads) are linked by flowlines which, by themselves, may also carry flow control devices like chokes and/or valves.

Various choke models are available such as constant Δ p, API 14B, Sachdeva, Perkins, Al-Safran and Kelkar, Hydro long, Hydro Short and Bernoulli w/Simpson multiplier.

The flowline models available depend on the problem PVT defined by the user. Pump operation may be characterized by fixed pressure differential, fixed power, or performance curves. Compressor type CAN be fixed-compression ratio, fixed power, centrifugal or reciprocating, with the compression process specified as isothermal, adiabatic, or polytropic. Terminal nodes (e.g., a separator) mark the boundary conditions of the network.

Inline Separation

The separation process can be setup as 2-phase (gas-liquid) or 3-phase (gas-oil-water) with additional options for incomplete oil separation and cooling.

The separator object can be defined as “inline” in scenarios such as when a degasser is used to separate gas from a liquid continuous flow and a deliquidiser is used to separate liquid from a continuous gas stream. The inline separator can be connected to two (gas -liquid separation) or three (gas-oil-water separation) outflow flowlines.

Reinjection

A source adds fluid to the system, typical with injectors connected to a network. Fluid injection is controlled by an input rate or a pressure.

It is possible to set the composition of the injected fluid when the PVT is defined as an Equation of State (EOS).

Produced fluid can also be reinjected e.g., for pressure maintenance purposes and enhanced recovery via gas lift reinjection or source reinjection.

Targets and Constraints

Schedules for network branches can be constant pressure at the separator or rate/pressure at the sources/sinks.

Wells disconnected from the network can have production targets assigned to them individually.

Constraints such as maximum oil/gas/water/liquid rate, maximum pressure and minimum pressure could also be enabled for the separator, source and sink respectively so that the simulation control automatically switches from the production target to constraint when the target is violated.

Network consistency

Prior to running computation on a surface network, Rubis-Network enables the user to first check the consistency of the network. The network can contain several independent branches, however there can be only one terminal node in each branch.

Steady State Computation

Ahead of running a fully transient network simulation, the validation option enables the user to perform a steady-state computation of the network using internally computed IPR for each well.

The operating point is computed from the well intake and IPR curves at each well. The user has the flexibility to select wells that are to be used as part of the computation as this allows steady-state simulation to be performed on a fraction of the entire network. This computation ensures that the network is proven and deployable for transient simulation.

A sensitivity option using a steady-state approximation allows the user to check the effect of different network element parameters on the overall flow conditions (rate, pressure, temperature, phase velocity and holdup) along the network.

Tuning IPR

The IPR matching option allows the user to constrain internally computed IPR to a field-measured data point for the well in question.

The tuned IPR provides an estimate of skin value which is used in the fully transient simulation to better model the well’s performance within the network.

Alarms

Alarms (i.e., warnings) are raised at appropriate network elements whenever flow constraints are violated, either in the steady-state computation or the fully transient simulation.

The user has the flexibility to set constraints in most network elements such as: maximum free gas permitted by pumps, maximum operable temperature of compressors and maximum water cut/GOR at wellheads.

Material-Balance-Driven grid

Coarse grid for material balance option is made available for the coupled network-reservoir model simulation.

The geometric grid remains unchanged; however, the model grid is aggregated. This reduces the number of computational grids and hence reduces runtime, while preserving the late-time response and the material-balance integrity of the system.

Output Visualizations

Additional network results include the simulated inflow and outflow gauges at all single node elements and snapshots of flowline results at every simulation time step.

These snapshots are displayed as flowline traverses from wellhead to the terminal node. Three new plots are created to present these additional results:

Network results plot, reservoir geometry plot and traverse plot.

In addition, all network results can be viewed in a tabular form accessible from any of the plots and Rubis main results dialog.