Page 84 - Intelligent Digital Oil And Gas Fields

Instrumentation and Measurement 55

Fluid current homogenization: This condition occurs when the state of the fluid
is closer to one single phase because of the mechanical principles. After sep-
aration at low pressure and low velocity, fluids can be separated, stratified, or
producing in a slug pattern. Some meters, especially turbines, cannot distin-
guish between gas and oil. Furthermore, at this condition the turndown can
change from 1.0 to 100 in minutes. To reduce this effect, mixers are used to
blend the gas, oil, and water; therefore, the liquid and gas travel at the same
mean velocity (V liq ¼V g ). The slip velocity is 1.0; in this condition, fluid
properties of the mixed fluids are a single value of viscosity, density, etc.
Homogenization allows turbine meters to measure fluid velocity with high
accuracy. Fig. 2.9 shows how a mixer can homogenize several fluids.
Separation system and efficiency: Well-location and gathering center oper-
ation use two- and three-phase separation equipment. After the separator
outlet, it is expected that the wellhead pressure drops by >60%; under this
condition, the flow regime could be a stratified pattern flowing at a laminar
flow regime. In this state, the flowmeter measures the flow with acceptable
accuracy. Three-phase separators are the most efficient devices to separate
water and gas from oil. In non-water production reservoirs, a two-phase
separator could be a good choice, but when the condensate or volatile oil
flow simultaneously with water, the total liquid production may represent
significant amounts of volume (GVF<0.5). A three-phase separation system
could be the best choice to measure oil, water, and gas separately. Generally,
after the separation outlet an orifice meter is used to measure the gas rate; at
the oil and water outlet, a turbine meter could be the most economical and
reliable choice. For a two-phase separation system, an infrared water cut
meter combined with a turbine meter is generally the right choice. The
net oil can be estimated by the total liquid measured from the liquid meter
times the water cut value of the water cut meter. Fig. 2.10 shows the best

Gas

Oil

Water

Fig. 2.9 A cross-section of the pipe showing how a stratified flow pattern can be
homogenized using a mixing tool.