# Fluid Gradient for Open Water

Fluid gradient for open water is an external profile, where the unknown is the external pressure profile of the tubing. The pressure profile consists of the hydrostatic salt water pressure to the wellhead, and the hydrostatic pressure from mud below.

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 for Open Water

## Inputs#

The following inputs define the fluid gradient for open water load case:

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 rig RKB, $\text{TVD}_{\text{RKB}}$

b. The wellhead/BOP interface, $\text{TVD}_{\text{WH/BOP}}$

c. The hanger of the tubing, $\text{TVD}_{\text{hanger}}$

d. The shoe of the tubing, $\text{TVD}_{\text{shoe}}$

3. The mud weight/density, $\rho_m$

4. The salt water density, $\rho_{sw}$

## Calculation#

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

$p_e = p_{\text{sw,WH}} + \rho_m \,g\,\left( \text{TVD} - \text{TVD}_{\text{WH/BOP}}\right)$

where $g$ is the gravitational constant, and $p_{\text{sw,WH}}$ is the hydrostatic salt water pressure at the wellhead given by:

$p_{\text{sw,WH}} = \rho_{sw}\, g\, \left(\text{TVD}_{\text{WH/BOP}} - \text{TVD}_{\text{RKB}}\right)$