Calculation of Injection Profiles

The wellhead pressure at an injection well can be calculated as the sum of several contributions (Carroll and Lui, 1997)  

For small acid gas injection schemes, the reservoir pressure and static head terms are the only ones of significance. In particular, it is assumed that the pressure drop due to friction is not important, although the design engineer is advised to review these factors in each case. Thus equation (9.1) reduces to  

In order to calculate the injection pressure, one integrates the differential hydrostatic equation from the reservoir conditions to the surface. The hydrostatic equation is  

Gases are compressible, that is, their density is a function of the temperature and the pressure. Thus when calculating the injection profile for a gas this fact must be accounted for. 

The simplest model of gas behavior is the ideal gas. The density of an ideal gas is calculated as follows  

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