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HPHT Gas Wells Control Using Swapping Method

IP.com Disclosure Number: IPCOM000241629D
Publication Date: 2015-May-18
Document File: 4 page(s) / 62K

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The IP.com Prior Art Database

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Mokhtar M. Elgassier: AUTHOR

Abstract

When a wellbore is completely or partially filled with gas and work over or drilling operations are to be carried out on the well, it is necessary to bleed off the gas and replace it with liquid or mud to maintain well control. The replacement of the gas in the wellbore by liquid is commonly done in small stages with gas being released after each stage. This procedure usually requires a long time and could lead to adverse consequences. The method proposed in this paper will enable engineers to determine in advance the exact volumes of liquid necessary to pump into the well and the exact volumes of gas to bleed off after each injection so the bottomhole pressure always stays above the formation pressure but below its fracturing pressure. The method takes into account the integrated pressure calculation due to a real gas column in the wellbore. Thus, the variation of the gas deviation factor with pressure and temperature of the gas in the wellbore is taken into consideration. The results obtained assuming real gas behavior vs. ideal gas can be significantly different in the number of stages, volumes calculated and pressures especially for deep HPHT wells. Three calculation procedures for the volumes and pressures are presented in the paper. These procedures are outlined step by step in the paper. The procedures are fast and eliminate the need for unnecessarily small injected liquid volumes and remove the element of guessing and the danger of unforeseen consequences.

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HPHT Gas Wells Control Using Swapping Method

Abstract

When a wellbore is completely or partially filled with gas and work over or drilling operations are to be carried out on the well, it is necessary to bleed off the gas and replace it with liquid or mud to maintain well control.

The replacement of the gas in the wellbore by liquid is commonly done in small stages with gas being released after each stage.  This procedure usually requires a long time and could lead to adverse consequences.

The method proposed in this paper will enable engineers to determine in advance the exact volumes of liquid necessary to pump into the well and the exact volumes of gas to bleed off after each injection so the bottomhole pressure always stays above the formation pressure but below its fracturing pressure.  The method takes into account the integrated pressure calculation due to a real gas column in the wellbore.  Thus, the variation of the gas deviation factor with pressure and temperature of the gas in the wellbore is taken into consideration.  The results obtained assuming real gas behavior vs. ideal gas can be significantly different in the number of stages, volumes calculated and pressures especially for deep HPHT wells.  Three calculation procedures for the volumes and pressures are presented in the paper.   These procedures are outlined step by step in the paper.  The procedures are fast and eliminate the need for unnecessarily small injected liquid volumes and remove the element of guessing and the danger of unforeseen consequences.

Method

Injecting liquid in a wellbore filled with gas will compress the gas and increase the bottom hole pressure (PBH ) to some desired maximum value Pmax that is below fracture pressure of the formation.  The fraction of the wellbore occupied by the compressed gas, x, to reach Pmax can be determined from the following equation:

                        (1)                  

Equation 1 can be solved either using Newton-Raphson method or Interval Halving (Bisection) method or the secant method.

Another way to solve for the volume of liquid injected is by incrementing the volume of the liquid and calculating the pressure at the bottom of the liquid column.  The following equation gi...