## Hydrostatic Pressure

Hydrostatic pressure is defined as the pressure due to the unit weight and vertical height of a column of fluid.

Hydrostatic Pressure = Fluid Density x True Vertical Depth

Note: It is the vertical height/depth of the fluid column that matters, its shape is unimportant.

Figure 1.1 Different shaped vessels

Since the pressure is measured in psi and depth is measured in feet, it is convenient to convert mud weights from pounds per gallon ppg to a pressure gradient psi/ft. The conversion factor is 0.052.

Pressure Gradient psi/ft = Fluid Density in ppg X 0.052 Hydrostatic Pressure psi = Density in ppg X 0.052 X True Vert. Depth

The Conversion factor 0.052 psi/ft per lb/gal is derived as follows:

A cubic foot contains 7.48 US gallons.

A fluid weighing 1 ppg is therefore equivalent to 7.48 lbs/cu.ft

The pressure exerted by one foot of that fluid over the area of the base would be:

7.48 lbs

144 sq.ins

Figure 1.2

Area definition of a cubic foot r r

Figure 1.1 Different shaped vessels

Figure 1.2

Area definition of a cubic foot

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

Example:

The Pressure Gradient of a 10 ppg mud

Conversion constants for other mud weight units are:

Specific Gravity x 0.433 = Pressure Gradient psi/ft

Pounds per Cubic Foot ^ 144 = Pressure Gradient psi/ft

### 1.3 FORMATION PRESSURE

Formation pressure or pore pressure is said to be normal when it is caused solely by the hydrostatic head of the subsurface water contained in the formations and there is pore to pore pressure communication with the atmosphere.

Dividing this pressure by the true vertical depth gives an average pressure gradient of the formation fluid, normally between 0.433 psi/ft and 0.465 psi/ft. The North Sea area pore pressure averages 0.452 psi/ft. In the absence of accurate data, 0.465 psi/ft which is the average pore pressure gradient in the Gulf of Mexico is often taken to be the "normal" pressure gradient.

Note: The point at which atmospheric contact is established may not necessarily be at sea-level or rig site level.

### 1.4 NORMAL FORMATION PRESSURE

Normal Formation Pressure is equal to the hydrostatic pressure of water extending from the surface to the subsurface formation. Thus, the normal formation pressure gradient in any area will be equal to the hydrostatic pressure gradient of the water occupying the pore spaces of the subspace formations in that area.

The magnitude of the hydrostatic pressure gradient is affected by the concentration of dissolved solids (salts) and gases in the formation water. Increasing the dissolved solids (higher salt concentration) increases the formation pressure gradient whilst an increase in the level of gases in solution will decrease the pressure gradient.

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

For example, formation water with a salinity of 80,000 ppm sodium chloride (common salt) at a temperature of 25°C, has a pressure gradient of 0.465 psi/ft. Fresh water (zero salinity) has a pressure gradient of 0.433 psi/ft.

Temperature also has an effect as hydrostatic pressure gradients will decrease at higher temperatures due to fluid expansion.

In formations deposited in an offshore environment, formation water density may vary from slightly saline (0.44 psi/ft) to saturated saline (0.515 psi/ft). Salinity varies with depth and formation type. Therefore, the average value of normal formation pressure gradient may not be valid for all depths. For instance, it is possible that local normal pressure gradients as high as 0.515 psi/ft may exist in formations adjacent to salt formations where the formation water is completely salt-saturated.

The following table gives examples of the magnitude of the normal formation pressure gradient for various areas. However, in the absence of accurate data, 0.465 psi/ft is often taken to be the normal pressure gradient.

 Formation Water Pressure psi/ft Gradient (SG) Example area Fresh water 0.433 1.00 Rocky Mountains and Mid-continent, USA Brackish water 0.438 1.01 Salt water 0.442 1.02 Most sedimentary basins worldwide Salt water 0.452 1.04 North Sea, South China Sea Salt water 0.465 1.07 Gulf of Mexico, USA Salt water 0.478 1.10 Some area of Gulf of Mexico

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

Figure 1.4

Figure 1.4

SECTION 1 : FUNDAMENTAL PRINCIPLES OF WELL CONTROL

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### Responses

• anonymous
what is hydro pressure well
9 years ago
• Griffo Gamgee
What is normal pressure in well control?
9 years ago
• Birikti
Why 0.052 in hydrostatic pressure?
9 years ago
• Liberio Cattaneo
Where is hydrostatic pressure in column of fluid?
9 years ago
• katharina
How is hydrostatic pressure measured in a well?
8 years ago
• steffen
How hydrostatic pressure affect the formation pressure in oil well?
8 years ago
• jonne
Why is the hydrostatic pressure from depth and weight are equivalent?
8 years ago
• Sanni
How to convert hydrostatic fluid height to water height?
7 years ago
• tero
How to control hydrostatic pressure?
7 years ago
• Jemma
What is the hydrostatic pressure at a depth of 5m in salt water?
7 years ago
• veli-matti
What is the conversion for ppm to percent to units of gas in drilling fluid?
7 years ago
• j scholz
How .052 for pressure derived?
6 years ago
• DOMINIK
What is normal pressure at 9850 feet in Gulf of Mexico?
6 years ago
• Mira
What is hydrostaic pressure in well control?
6 years ago
• Heidi
How is hydrorostatic pressure derived?
6 years ago
• HOLFAST
What is the hydrostatic head of a gallon of water?
5 years ago
• hiwet
How to control high hydrostatic head pressure at depth?
5 years ago
• evangelina
What is the fluid density in ppg for gulf of mexico?
5 years ago
• Elena
HOW TO FIGURE HYDROSTATIC PRESSURE ON A DIRECTIONA WELL?
5 years ago
• KACIE
How to get conversion factor 0.052?
4 years ago
• RUFINA
How is .052 derived in well control?
4 years ago
• alma
How to get conversion factor for hydrostatic pressure?
4 years ago
• MAXIMILIAN SCHNEIDER
How to kill a well with hydostatic water?
3 years ago
• Aloisia
How to get water pressure gradient 0.433?
3 years ago
• ida
How to figure a high pressure gas well hydrostatic pressure?
3 years ago
• abel
How to figure the kill weight of the hydrostaic pressure?
3 years ago
• Naomi
What is hydrostatic gradient?
3 years ago
• WIKTOR
How to calculate pressure gradient of a well when given specific gravity and density?
2 years ago
• demsas
What is normal oil gradient?
2 years ago
• Maxima
WHAT are the factors of hydrostatic pressure?
2 years ago
• joonas
How to derive the formula of 0.052 psi factor?
2 years ago
• ghenet
What is hydrostatic pressure in petroleum?
1 year ago
• Miska
Is normal hydrostatic pressure measured from seal level or sea bed?
1 year ago
• Nile
What is the fluid gradient of a column of 11.2 lb. /gal mud?
1 year ago
• Cailean Wilson
How to control subsurface pressures?
11 months ago
• Susie
How to convert sg of gas to pressure gradient?
10 months ago
• Kathryn Hughes
Which is true about the pressure of a fluid at a specific depth?
10 months ago
• Almaz
What is 0.052 in the hydrostatic pressure equation?
9 months ago
• russell
How is gradient of .052 0btained?
7 months ago
• ines
How to find the hydrostatic pressure of a kick?
4 months ago
• leon griffith
How to convert pore pressure to density?
3 months ago
• hollie
What happens when mud weight is smaller than the pore pressure?
2 months ago
• Verdiana
What is the average pressure gradient?
2 months ago
• Kalervo
How to calculate hydrostatic pressure at bottom of well?
2 months ago
• abbey
How to calculate hydrostatic pressure in water well?
1 month ago