What are the characteristics of a pressure gradient?
Characteristics of the pressure gradient based on 7 flow patterns were carefully discussed. It was found that the pressure gradient increased with the increase of gas superficial velocity and oil-water mixture velocity. However, characteristics of the pressure gradient became complex with the increase of input water cut.
What is normal pressure gradient?
The normal hydrostatic pressure gradient for freshwater is 0.433 psi/ft, or 9.792 kPa/m, and 0.465 psi/ft for water with 100,000 ppm total dissolved solids (a typical Gulf Coast water), or 10.516 kPa/m. Deviations from normal pressure are described as high or low pressure.
What is the equation for pressure gradient?
Pressure Gradient = Pressure × [Distance] -1 . . . . (1) The dimensional formula of distance = [M 0 L 1 T 0] . . . . (2) ⇒ Pressure = Force × [Area] -1 . . . . (3) ∴ the dimensions of force = [M] × [L 1 T -2] = [M 1 L 1 T -2] . . . (4) And, the dimensional formula of area = [M 0 L 2 T 0] . . . (5)
What is the definition of pressure gradient?
What is the definition of pressure gradient? In atmospheric science (meteorology, climatology and related fields) Pressure gradient (typical for air, more general for any liquid) is a physical quantity that describes in which direction and at which speed the pressure increases fastest around a given location.
What is an example of a pressure gradient?
The most consistent pressure gradient in Earth's atmosphere is the decrease in air pressure that occurs as altitude increases. This pressure gradie...
What causes pressure gradient?
Pressure gradients have many causes. But within Earth's atmosphere, most pressure gradients are caused by uneven heating of Earth's surface.
What is the pressure gradient formula?
The most common form of the pressure gradient formula is PG = PD/D. In this formula, the variable PG stands for pressure gradient, PD stands for pr...
What is hydrostatic pressure gradient?
The hydrostatic pressure gradient is the rate of change in formation fluid pressure with depth. Fluid density is the controlling factor in the normal hydrostatic gradient. In the U.S. Rocky Mountains, a formation water gradient of 0.45 psi/ft is common. In the U.S. Gulf Coast, a gradient of 0.465 psi/ft is common.
What factors must be taken into account when estimating fluid pressure at depth?
Pressure. Fluid composition (including dissolved gases and solids) Fluid phase—gaseous or liquid. These factors must be taken into account when estimating fluid pressure at depth. The small amount of dissolved gas contributes little to the density and can be ignored in the exploration state.
Why does oil density vary?
Oil density varies greatly because of the large variety of oil compositions and quantity of dissolved gases. Also, oil composition is inherently much more variable than formation water composition.
Is gas density a liquid or gas?
Gas density is strongly affected by pressure, temperature, and composition. In the reservoir, gas may be in the liquid phase; if so, we should treat it as a very light oil.
How much pressure does a gradient of 0.425 psi/ft at 2000 ft.?
From the previous example, a gradient of 0.425 psi/ft at 2000 ft. resulted in 850 psi pressure.
How to find pressure at a given depth?
To find a pressure at a given depth, simply multiply the VERTICAL depth by the given fluid gradient.
What happens when fluid doesn't reach surface?
If the fluid doesn’t reach the surface, then there is some ‘fluid level’, or depth, where the pressure is zero and then the pressure increases according to the gradient.
What is the density of pure water?
The density of pure water is 1000 kg/m3. To convert to gradient:
Do you need to calculate specific gravity?
Most of the time you will not be given a fluid gradient or an average specific gravity, you will need to calculate it.
Can we calculate the equivalent fluid column if we know the pressure and the gradient?
Similarly, if we know the pressure and the gradient, we can calculate the equivalent fluid column resulting from that pressure.
What is the window between the formation pressure gradient and the pore pressure gradient?
It is usually called a window, namely the window between the formation fracture pressure gradient and the pore pressure gradient. Due to the increasing depth of the deep sea, and the decreasing fracture pressure gradient, the window between the formation fracture pressure gradient and the pore pressure gradient is very narrow.
What is the pore pressure gradient?
The pore pressure gradient is the maximum pressure gradient of oil and gas fluid in the formation pore. In order to control the well and prevent blowout, we need to adjust the density of drilling fluid to make sure that the pressure of the bottom is higher than the maximum pore pressure gradient, and also control the density of drilling fluid to make the mud column pressure less than the minimum formation fracture pressure gradient. So, for a certain depth of well, the adjustable density range of drilling fluid can be formed between the formation fracture pressure gradient and the pore pressure gradient. It is usually called a window, namely the window between the formation fracture pressure gradient and the pore pressure gradient. Due to the increasing depth of the deep sea, and the decreasing fracture pressure gradient, the window between the formation fracture pressure gradient and the pore pressure gradient is very narrow. The relationship between the formation fracture pressure gradient and the pore pressure gradient changes with the variation of the depth of water and affects the window ( Figure 4-3 ). The influence of the low fracture pressure gradient of deep water formations on deep-water oil and gas engineering is discussed in the following:
How does fracture gradient affect pore pressure?
As water depths increase in offshore drilling, the fracture gradient and the pore pressure gradient values become closer and closer together. This is caused by the fracture gradients being considerably lower as the water depth increases. Fracture gradients depend upon the overburden stress. When rock is replaced by seawater, the average overburden density (and corresponding stress) decreases. For example, the effect of water depth for two different water depths is shown in Table 5.6.
How many feet is a vertical well?
A vertical well was cased with surface casing at 2000 ft. Below the casing shoe, several weak zones were expected. Those zones had subnormal pore pressure (pore pressure gradient 3 to 7 ppg). The base of the weak zones was at about 6000 ft. Further down the well path, pressured zones were expected, with the pore pressure gradient of 9.5 ppg. To meet this elevated pore pressure, the mud weight had to be increased while drilling the pressured zones. This could, however, induce losses in the subnormally pressured weak zones higher up the well.
What is fracture gradient?
Fracture gradient here refers to the fracture pressure gradient, namely the minimum pressure gradient of the formation fracture. For formations with similar thick sedimentary layers, with increasing water depth, the fracture pressure gradient of the formation reduces, as shown in Figure 4-2.
How much penetration is required for a 30 in conductor?
The 30 in. conductor casing is set with about 100 m penetration. The fracture gradient below the 30 in. casing is fairly low. Therefore, in the 26/24 in. hole, the mud weight is below the median line during most of the interval.
Who proposed the empirical equation for pore pressure gradient prediction from sonic compressional transit time?
Eaton (1975) proposed the following empirical equation for pore pressure gradient prediction from sonic compressional transit time: