## In this document we describe the external gradient Fluid gradient available in Oliasoft WellDesign.#

Fluid gradient is an external profile, where the unknown is the external pressure profile of the tubing. As the name suggests, the external pressure profile is given by the hydrostatic pressure of a single fluid column.

NOTE!
In this documentation we denote any tubular as casing or tubing. All calculations however encompass any tubular, such as tubings, casings, liners, tie-backs etc.

### Printable Version#

Oliasoft Technical Documentation - Fluid Gradient (Single)

## Inputs#

1. The true vertical depth (TVD) along the wellbore as a function of measured depth. Alternatively, the wellbore described by a set of survey stations, with complete information about measured depth, inclination, and azimuth.

2. The true vertical depth (TVD) of: a. The hanger of the tubing $\text{TVD}_{\text{hanger}}$ b. The shoe of the tubing $\text{TVD}_{\text{shoe}}$

3. The mud weight / density $\rho_m$

## Calculation#

The external pressure profile, parametrized by TVD, of the tubing is then given by:

$p_e = \rho_m \,g\,\text{TVD}$

where $g$ is the gravitational constant.