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Lost Returns with Mud Drop

In this section we describe the load case "Lost Returns with Mud Drop" available in Oliasoft WellDesign™.​


Lost returns with mud drop is a collapse load case, where the unknown is the internal pressure profile of the casing / tubing.



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. //: # (end - note)


Summary​

Lost returns with mud drop represent a collapse load that can occur while drilling. This phenomenon reflects a sudden influx of drilling mud into the formation, resulting in a mud drop. Initially, the pressure is established at the casing shoe, which is the sum of the pore pressure and atmospheric pressure. As we move from the casing shoe to the level of the mud drop, the pressure is determined by the mud gradient. If the mud drop occurs below the hanger, the internal pressure remains at atmospheric pressure from the mud drop level to the hanger.


Illustrating Pressure Profile Graph​

Printable Version​

Oliasoft Technical Documentation - Lost Returns with Mud Drop


Inputs​

The following inputs define the lost returns with mud drop 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 hanger of the tubing, TVDhanger_{hanger}
    2. The shoe of the tubing, TVDshoe_{shoe}
    3. The lost returns depth, TVDLR_{LR}
  3. The pore pressure profile from hanger to shoe
  4. The mud weight/density, ρmud\rho_{mud}
  5. The atmospheric pressure, with default value patm=101325 Pap_{atm} = 101325\ Pa //: # (end - inputs)

Scenario Illustration



Calculation​

The internal pressure profile of the tubing is calculated as follows

  1. Calculate the pore- pressure and density at the lost returns depth, pp,LRp_{p,LR} and ρp,LR\rho_{p,LR} , respectively

  2. Calculate the true vertical dpeth of the mud level,

    TVDmud=(1−ρp, LRρmud)TVDLR                                         (1)\text{TVD}_\text{mud} = \left(1 - \frac{\rho_\text{p, LR}}{\rho_\text{mud}} \right) \text{TVD}_{\text{LR}}\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\ (1)

    The rationale behind this calculation is that the hydrostatic pressure of the lost mud should equal the pore pressure at the lost return depth.

  3. The internal pressure profile in the tubing, parametrised by TVD, is given by

    pi={patm,TVD<TVDmudmaximum(patm,patm+pp, LR−ρmud g(TVDLR−TVD)),else,                                         (2)p_i = \begin{cases} p_\text{atm}, \qquad \text{TVD} < \text{TVD}_\text{mud} \\ \text{maximum}(p_\text{atm}, p_\text{atm} + p_\text{p, LR} - \rho_\text{mud}\, g\left(\text{TVD}_{\text{LR}} - \text{TVD} \right)), \qquad \text{else},\end{cases} \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\ (2)


where gg is the gravitational constant.