Page 35 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 29

3. Calculate the hydrostatic pressure of the fresh water column.
ð2250 1400Þ 3 ð1000=102Þ 5 8333 kPa

4. Calculate the hydrostatic pressure of the formation water column.
ð2800 2 2250Þ 3 ð1160=102Þ 5 6254 kPa
11; 734 1 8333 1 6254 5 26;321 kPa

1.1.6.2.1 Surface pressure
Intervention work is frequently carried out on wells with pressure to sur-
b
face. Surface pressure (Shut in Tubing Pressure, or SITP ) must be
included when calculating bottom-hole pressure (BHP). Add SITP to the
hydrostatic pressure.

1.1.6.3 Gas hydrostatic pressure
Gas hydrostatic pressure is calculated in one of three ways:
1. Use of a gas correction factor (from tables).
2. By calculation using formula.
3. If the gas gradient is known, by multiplying by the depth (TVD).
In dry gas wells, the gas column will reach from the surface to the res-
ervoir. In liquid-producing wells, the depth of the gas/liquid contact is
needed. Some of the pressure calculations require additional information
that may or may not be available at the well site; average wellbore tem-
perature and the compressibility (Z factor) of the gas.
Method 1: Using gas correction tables (Tables 1.5 and 1.6)
To calculate gas hydrostatic pressure:
• Find the appropriate gas gravity in the row along the top of the table.
• Find the well depth (TVD) in left hand column.
• Use the correction factor where the depth row intersects the gas grav-
ity column.
• Correction factor 3 SITP 5 gas pressure at the required depth. The
result includes both surface pressure and gas hydrostatic pressure.
The gas correction factors in the tables were calculated using the for-
mula below:

SG 3 D
Correction factor 5 e 28812:47 Þ (1.9)
ð

b
The abbreviation CITP’ (closed in tubing pressure) is sometimes used instead of SITP.
Also used are the abbreviations SITHP (shut in tubing head pressure) and CITHP,
closed in tubing head pressure.