Preparation of hydrocarbon foam Materials

Production of self-generating foams

Introduction

Foam is highly concentrated dispersed system in which the dispersed phase is gas and liquid is dispersion medium. Stable foams are prepared in the presence of a third component - foam-former. At low concentration gas-liquid systems bubbles are far from each other (for example, carbonated water containing bubbles of carbon dioxide), such systems are characterized by low sedimentation stability and short lifetime.

Foam can be a gas-liquid system with cell-membrane structure in which individual bubbles are connected with each other by separation films forming a general framework. In foam a bubble is trapped between other bubbles adjacent to it. Such tight packing is achieved at a certain ratio of liquid and gas. With a significant saturation of the foam by gas, bubbles lose spherical shape and turn into polyhedrons, while their separation films get the same thickness throughout the entire volume of foam.

High-concentration foam, due to excess gas-phase and cross-compression of gas bubbles, are composed of polyhedral cells that have honeycomb structure and are the most stable. The strength and duration of existence the foam depends on the properties of the filmframe, in turn, determined by the nature and amount of present in the system surfactant - foam-former. Molecules of foam-former concentrate in the surface layer between the liquid and air phases.

In practice, the basic liquid phase of foam systems can be water and water solutions, hydrocarbons, and methanol. Foam systems are used in the processes of drilling, drilling-in the reservoir, development of wells, washing off sand plugs, hydraulic fracturing, for enhanced oil recovery and well productivity.

Gas is dissolved in a liquid foam-forming solution during its injection into the well. The solubility of gases in liquids varies widely and depends on the nature of the solvent, temperature and pressure. Table. 2 shows data on the solubility of certain gases in water at 18 ° C and pressure of 0.1 MPa.

Table 2

Data on the solubility of gases in water

Gas	Volumes of gas dissolved in a volume of water	Gas	Volumes of gas dissolved in a volume of water
Helium	0,0139	Chlorine	2,40
Nitrogen	0,01698	Sulfur Dioxide	42,36
Hydrogen	0,01863	Hydrogen chloride	427,90
Oxygen	0,03220	Ammonia	748,80
Carbon dioxide	0,9280	-	-

As seen from Table 2, in one volume of water dissolves 748.8 of ammonia and only 0.017 volume of nitrogen. The high solubility of ammonia, hydrogen chloride, sulfur dioxide, chlorine, and carbon dioxide is due to their chemical interaction with water. Solubility of gases contribute to an increase in pressure and prevent the increase in temperature. Therefore, when applying foam systems in the process of oil extraction, you should always take into account the depth of the wells and reservoir pressure and temperature. The use of a gas can also be restricted by its high cost, low values ​​of maximum permitted concentrations (MPC), corrosion and explosiveness, and therefore the most appropriate gas phase to produce foam is nitrogen.

Self-generating foams are used for well development and as the dispersed gas phase contain nitrogen.

For nitrogen the following oxidation-reduction reaction is used that passes between ammonium chloride and sodium nitrite in an acidic environment. In its simplest form, this reaction can be written as follows:

NH₄Cl + NaNO₂ ® NaCl + N₂­ + 2H₂O, при рН £ 3.

The foam is formed by adding to the solution of foam-forming agent. Feature of the method is to use as an agent to maintain the acidic environment and,simultaneously, foam-forming agent alkyl phosphoric acid (alkyl phosphate "Himeko"). The application of this agent, on the one hand, allows to withstand the pH within a narrow range (pH 2-3), which guarantees that the reaction goes toward the formation of nitrogen, but not it’s oxides (for example NO2), and, on the other hand - will allow to get stable foam both in water and in hydrocarbon medium.

Method of work performance
Equipment

1.Glass cylinder 1000 ml;
2. Glass cylinder of 50 ml;
3. Glass beaker, 100 ml;
4. Glass beaker, 50 ml;
5. Syringe 2 ml;
6. Glass rod;
7. Laboratory balance accurate to 0.01 g;
8. Water bath with heating device.

How to obtain water foams

Materials

1. Fresh water;
2. Sodium nitrite - powder;
3. Ammonium chloride - powder;
4. Neftenol VVD;
5. Alkyl phosphate "Himeko."

Carry out the experiment under the hood!

Measure out 45 ml of heated fresh water in cylinder, pour it into a glass beaker of 100 ml. A weighed sample of ammonium chloride - 5 g and sodium nitrite - 6 g, place in a beaker with water and dissolve by stirring with a glass rod. In the resulting true solution inject with a syringe 0.55 ml of Neftenol VVD and gently stir, not whipping the foam. Measure out 10 ml of fresh water in cylinder, pour it into a glass of 50 ml and inject there through a syringe 2 ml of alkyl phosphate "Himeko", stir it with a glass rod.

In the pre-heated to 80 ° C water bath set a cylinder for 1000 ml and pour there both solutions, the contents of the cylinder mix slightly .

The resulting foam is observed within 30 min. Determine the time during which the maximum amount of foam is produced and calculate the multiplicity of foam: К=V_m/V_liq ,
where Vm - the maximum amount of foam;
Vliq - the initial volume of liquid (62 ml).

Preparation of hydrocarbon foam Materials

1. Fresh water;
2. Oil;
3. Sodium nitrite - powder;
4. Ammonium chloride - powder;
5. Alkyl phosphate "Himeko."

Carry out the experiment under the hood!

Measure out 100 ml of oil into a cylinder , pour it into a glass beaker of 100 ml and with a syringe administer there 1 ml of alkyl phosphate "Himeko", stir it with a glass rod. Measure out 45 ml of heated fresh water into a cylinder , pour it into a glass beaker for 50 ml. The prepared batch of: ammonium chloride - 5 g and sodium nitrite - 5 g, place in a beaker with water and dissolve by stirring with a glass rod.

In the pre-heated to 80 ° C water bath set a cylinder for 1000 ml and pour there both solutions, the contents of the cylinder mix slightly .
The resulting foam is observed within 30 min. Determine the time during which the maximum amount of foam is produced and calculate the multiplicity of foam:

К=V_m/V_liq ,

· where Vm - the maximum amount of foam;

· Vliq - the initial volume of liquid (150 ml).

Self Test Questions

1. Give the classification of the foams and name their characteristics.
2. How to determine the kinetic stability of the gas foam?
3. Explain the essence of the key factors of stability of gas foams.
4. Give examples of undesirable formation of gas foams in oil-technological processes and indicate ways to prevent their formation.
5. What are the requirements for foams used in the oilfield practice?