Factors Affecting Emulsion Stability




From a practical standpoint, emulsion stability is the most critical data for analyzing oil water emulsions. The higher the degree of emulsion stability, the more difficult it is for the oil and water to be separated. Insight into the factors affecting the stability of these oil in water emulsions will provide a greater understanding into the breaking, or de-emulsification of these emulsions. Under normal circumstances, viscous and heavy crude oils (in which SAGD operations is economically viable), the crude oil contains natural emulsifiers which will help to stabilize emulsions by increasing kinetic stability.

Specifically, several factors affect the emulsion stability of reverse emulsions, they are as listed
  • Presence of surfactants which cause the oil to be dispersed in the water as very small droplets.
  • Shearing of the fluid during production, in which the steam flooding causes the generation of smaller droplets, which increase the emulsion
  • Higher organic density of the organic compounds in the emulsion increases the stability of the emulsion
  • Presence of fine solids such as clays, sands, or corrosion products injected during production increases the stability of the emulsion

It is noted that contrary to normal water in oil emulsions, temperature of the crude oil does not play a significant factor into the stabilizing the emulsion for reverse emulsions. This is caused by a minor viscosity change in the oil phases with temperature increase and as such, increasing fluid temperature is not a solution to eliminating oil in water emulsions.

Due to the constantly variable conditions in the reservoir, lab results investigating the effects of emulsion stability general involves agitation of a sample fluid simulated at reservoir conditions under varying conditions. Figure 1 shows a sample of this test, and results from these types emulsion stability experiments are synthesized below.
emulsionbottles.jpg
Figure 1: Typical emulsion testing involving observations of emulsion settling


1. Effect of Surfactants on reverse emulsion stability




The hydrophilic lipophilic balance (HLB) values of a particular surfactant is a measure of the degree to which the particular substance is hydrophilic (tendency to dissolve in water) or lipophilic (tendency to dissolve in non polar solvents, fats oils and lipids) , as proposed by Griffin in 1949. Surfactants with HLB values between 8 and 18 specifically are determined to be oil in water emulsifiers, which promote the stability of reverse emulsions. This stabilization effect is generally the result of a positive or negative charge induced on the droplets due to the surfactants, resulting in a higher attraction between the polar water molecules and the charge induced droplets.
These reverse emulsion emulsifiers with HLB values between 8 and 18 are sourced from the following potential sources:

  • Acidizing/Fracturing stimulation
Acidizing or fracturing stimulations is used in oil wells to increase production. Acid stimulations involve acid injections around the wellbore to eliminate fouling impediments and restore production. Fracturing stimulations is used to increase flow through the formation by creating actual fractures in the formation, allowing for higher flow rate. The surfactants used in these types of production stimulations such as GasPerm 1000 have high HLB values, and may a potential source of emulsifying surfactants.
  • Surfactants from water used during steam injection
Certain surfactants with high HLB values may be injected into the water during certain oil productions to enhance the oil recovery. The additives present in this injection water such as biocides may also lead to oil in water emulsions.
  • Corrosion Inhibitors
Amine corrosion inhibitors that are commonly applied during the production of crude oil may also have high HLB values that can result in reverse emulsions.

2. Effect of Crude Oil and Particles on Reverse Emulsion Stability




Water oil emulsion de-emulsifiers is sometimes applied during crude oil production in order to prevent water oil emulsions, these surfactants generally have an HLB value greater than 6 and although they may prevent water in oil emulsions, they may potentially cause oil in water emulsions. This effect however, depends on the crude oil composition and thus further field tests in this area are needed for optimal oil water separation.

The presence of asphaltene, wax and fine calcium carbonate particles also affects the emulsion stability. Below is an excerpt of the laboratory results conducted by Saudi Aramco on the effect of these particles on emulsion stability. It is noted that water cut is a general term used in oil production to describe the ratio of water produced to the volume of total liquids produced.

An increasing trend in emulsion stability is noticed with increasing calcium carbonate concentrations, and the problem is worsened when the carbonate particles are wetted (coated) by asphaltene.

Table 1: Effect of CaCo3 Particles on ABJF Oil/Water Emulsion stability at 60°C, courtesy of Saudi Aramco Southern Area Laboratories Division

Observations of Water separation and emulsion volume
ABJF Crude with 5% Water cut
Crude + 50mg/L CaCo3
Crude + 100mg/L CaCo3
Crude + 500mg/L CaCo3
Crude + 50mg/L CaCo3 coated with asphaltene
Crude + 100mg/L CaCo3 coated with asphaltene
Crude + 500mg/L CaCo3 coated with asphaltene
Shear strength
Low shear in shaker for two minutes
Test Temperature
60°C
Free Water Volume (%)
Settling for 30 minutes
5
4.8
5
4.5
4.5
4.5
Settling for 120 minutes
5
5
5
4.5
1.5
0.5
After Centrifuging for one minute
Free Water Volume (%)
5
5
5
5
5
5
Emulsion Volume (%)
0
0
0
0.5
0
0.5
CaCo3 Volume (%)
0.1
0.2
0.5
0.1
0.2
0.5
Shear strength
Medium shear in shaker for ten minutes
Test Temperature
60°C
Free Water Volume (%)
Settling for 30 minutes
4
4
4
2
1.5
1
Settling for 120 minutes
4.5
4.5
4
2.5
2
2
After Centrifuging for one minute
Free Water Volume (%)
5
5
5
5
5
5
Emulsion Volume (%)
0
0
0
1
1
1
CaCo3 Volume (%)
0.1
0.2
0.5
0.1
0.2
0.5

3. Effect of shearing in reverse emulsion stability



Water in oil emulsions and reverse emulsions share the same characteristic that higher shear strength results in a more stable emulsion. The following lab information is synthesized from shearing tests conducted by Saudi Aramco. An increasing trend of emulsion stability is noticed with the increasing shear strength (less settling is observed).

Table 2: Effects of Water cut and shear on ABJF Oil/ Water Emulsion Stability at 60°C, courtesy of Saudi Aramco Southern Area Laboratories Division

Observations of Water separation and emulsion volume
Water Cut (%)
5
10
15
20
25
30
Shear strength
Low shear in shaker for two minutes
Test Temperature
60°C
Free Water Volume (%)
Settling for 30 minutes
4.0
10
15
20
23
26
Settling for 120 minutes
4.5
10
15
20
25
30
After Centrifuging for one minute
Free Water Volume (%)
5.0
10
15
20
25
30
Emulsion Volume
0
0
0
0
0
0
Shear strength
Medium shear in shaker for ten minutes
Test Temperature
60°C
Free Water Volume (%)
Settling for 30 minutes
3.0
8.0
10
15
15
18
Settling for 120 minutes
4
9
13
18
20
25
After Centrifuging for one minute
Free Water Volume (%)
4
9
14.5
19
20
25
Emulsion Volume
2
3
3.5
2
7
7