Making a simple steady state model more appropriate for underbalanced drilling

Abstract

In an underbalanced operation the well needs to be kept in underbalanced conditions at all time. That is, from the beginning to the end of the drilling process. This is necessary to keep well from formation damage and potential hazardous drilling problems such as lost circulation and differential sticking.

With flow modeling, it is possible to simulate an underbalanced drilling operation scenario, with given liquid and gas injection rates, and also production influx.

The concept of steady state modeling is that the amount of mass going in to the system, is the same amount of mass coming out of it.

By using Matlab programming language, and the implementation of the numerical method of “Halving the interval”, it has been possible to find the bottomhole pressure of a underbalanced well with guessing. The guessing has been necessary to start the whole looping process with the method of “Halving the interval”.

Some changes of liquid rates versus gas rates has been made to plot those values in to graphs, showing a trend for the various combination of rates, production influx and different choke pressures.