This paper describes the development of an advanced simulator for modelling the Suffield gas field in full detail. Suffield is the largest gas field in Canada operated by one company. The simulator must be capable of handling over 4000 wells producing from 3 horizons.
The simulator- solves the reservoir and gathering system models at the same time. The solution proceeds in sequential fashion between the reservoir and gathering system, with the well model acting as the boundary condition for each model.
The surface model is fully implicit, capable of handling multiple terminals and looped lines. Boundary conditions for the surface model Can be either rate or pressure, and can be specified either at the terminal level or at the battery level. An innovative feature of the surface model is the ability to model controllers, which cause the problem to degenerate into a number of smaller problems, each of which must be solved separately.
The three dimensional single phase reservoir model is also fully implicit, as is the well model. A significant feature of the well model is the cross-flow capability in multilayer completions.
The large amount of data used in the model is supported by a database manager and a graphics preprocessorfor digitizing and displaying the surface network.
Although the simulator was developed for a specific application, it is completely general and is applicable to any gas field.
For design and analysis purposes, the importance of simultaneously simulating the reservoir and gathering system performance has been recognized for some time. This type of model was pioneered by Dempsey et al1, with subsequent developments emphasizing the surface system simulation (e.g., Berard and Eliason2, Agbi3). The surface system in Dempsey et al is restricted to a tree type of structure (i.e., only one terminal point; loops are not allowed) and the explicit solution technique employed on the gathering system suffered poor stability. Subsequent developments introduced implicit technique for the gathering system, but reduced the reservoir model to material balance or tank type models, eliminating the ability to see transient and interference effects in the reservoir. Because or the areal extent and the number of wells in Suffield, it is important to be; able to resolve such effects. This model contains a fully implicit three dimensional single phase reservoir model, plus a fully implicit efficient gathering system model.
The following sections describe the overall solution algorithm, and the novel features of the gathering system, reservoir and well models. Numerical and implementation concerns will be discussed. Because of the vast body of literature on the reservoir modelling side (see, e,g., Aziz and Settari1), the reservoir model will be discussed only briefly.
The overall problem is large and complex. To make it tractable, the solution algorithm breaks it up into two smaller ones which are solved separately and repeatedly in sequential fashion. The two major steps are
solve the gathering system equations with outlet boundary conditions being specified by the user and inlet boundary conditions being reservoir grid pressures held constant for this phase of the solution,
