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Fluid Gradients (Dual)

Fluid gradients (dual) is an external profile, where the unknown is the external pressure profile of the tubing. The pressure profile consists of the hydrostatic pressure from a fluid above and a fluid below the top of cement (TOC).

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.


The following inputs define the fluid gradients (dual) external profile:

  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, TVDRKB\text{TVD}_{\text{RKB}}

    b. The hanger of the casing / tubing, TVDhanger\text{TVD}_{\text{hanger}}

    c. The shoe of the tubing, TVDshoe\text{TVD}_{\text{shoe}}

  3. The fluid density above top of cement, ฯm\rho_m

  4. The fluid density below top of cement, ฯc\rho_{c}


The external pressure profile above and including TOC, parametrized by TVD, of the casing / tubing is then given by:

pTOC=ฯmโ€‰gโ€‰TVDTOCp_{\text{TOC}} = \rho_{m}\, g\, \text{TVD}_{\text{TOC}}

where gg is the gravitational constant, and pTOCp_{\text{TOC}} is the hydrostatic fluid pressure at top of cement. The pressure below TOC and including the casing / tubing shoe is thus:

pshoe=ฯcโ€‰gโ€‰(TVDshoeโˆ’TVDTOC)+pTOCp_{\text{shoe}} = \rho_{c}\, g\, \left(\text{TVD}_{\text{shoe}} - \text{TVD}_{TOC} \right)+ p_{TOC}