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Casing Evacuation

In this section we describe the load case "Evacuation" available in Oliasoft WellDesign™".​


Casing evacuation is a collapse load case, where the unknown is the internal pressure profile of the tubing. The scenario is that all or part of the mud being displaced out of the wellbore. //: # (end - introduction)

NOTE!
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.


Summary​

Casing evacuation is a collapse load case where the internal pressure profile is given by zero surface pressure with hydrostatic air column from RKB to mud level and hydrostatic mud column from mud level to the casing shoe. Worst case scenario is full evacuation where mud level is set to casing shoe depth and the whole casing is filled with air.

Illustrating Pressure Profile Graph​

Printable Version​

Oliasoft Technical Documentation - Casing Evacuation //: # (end - printable_version)


Inputs​

The following inputs define the casing evacuation 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
    1. The rig RKB, TVDRKB_{RKB}
    2. The hanger of the tubing, TVDhanger_{hanger}
    3. The mud level, if any, above the shoe, TVDmud_{mud}
    4. The shoe of the tubing, TVDshoe_{shoe}
  3. The fluid weight/density of mud, ρmud\rho_{mud}
  4. Air density, ρair\rho_{air}. Default value ρair\rho_{air} = 1.225 kg/m3^3 //: # (end - inputs)

Calculation​

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

pi={ρairgTVD,TVD≤TVDmudpair+ρmg(TVD−TVDmud), else                                          (1)p_{i}= \begin{cases}\rho_{\mathrm{air}} g \mathrm{TVD}, & \mathrm{TVD} \leq \mathrm{TVD}_{\mathrm{mud}} \\ p_{\mathrm{air}}+\rho_{m} g\left(\mathrm{TVD}-\mathrm{TVD}_{\mathrm{mud}}\right), & \text { else }\end{cases}\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\ (1)

where gg is the gravitational constant, and

pair=ρairgTVDmud                                         (2)p_{air} = \rho_{air}gTVD_{mud}\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\ (2)