This paper presents a system modeling program, designed for use on a microcomputer, which calculates steady-state pressures and flowrates for a single-phase gas or water system. The program can model flow through 1) well completions using IPR formulas; 2) flow lines (inclined, vertical, or horizontal); 3) fixed orifice chokes; 4) and single- or multi-stage reciprocating compressors. The program uses nodes to identify pressures and node connecting elements to identify flowrates and determine which type of element that is being modeled.
The program determines unknown pressures by either sequential or simultaneous methods. In the sequential method the program analyzes each node connecting element individually. The simultaneous solution creates a matrix containing flow balance equations from each node in the system. Next, the program solves this matrix simultaneously to determine values for the unknown pressures and flowrates. The purpose of this paper is to explain the logic of the modeling program and demonstrate its applicability in a microcomputer environment using examples.
Surface facility modeling is an important tool in the design of new facilities as well as the monitoring of existing facilities. A good model should be able to solve the unknown variables in the network in a relatively short period of time. Second, the model should show the effects of changes in design parameters over the entire network.
Several factors important in designing a good modeling program are: modeling approach, solution method, and flow equations. Steadystate flow through the network will be assumed in the construction of the model. Various computer models using the steady-state approach to facilities modeling have been available for quite some time. The program's solution method should follow the guidelines of a good model. A simultaneous solution method can solve for the unknowns in a network quickly and can show the effect on the network of changes in design parameters. Another method which can be used to solve for unknown pressures and flowrates in the network is the sequential method. However, this method will not show the effects on the network of changes in design parameters. Finally, the program should offer a wide variety of flow equations for determining the effects of different types of flow elements on the network.
This paper presents a steady-state modeling program with two solution techniques available for microcomputer application. The program uses either a sequential or a simultaneous iterative technique to solve for unknown pressures and flowrates in an existing system. The sequential technique allows the engineer to solve a system much faster than the simultaneous iterative technique. This reduction of CPU time is of great importance when trying to solve large systems on a microcomputer.
Another important part of the network program is the type of flow elements that it can model.