8.3. Sar (surface-active reagent) composition.

Surface-active reagents (SAR) are chemical compositions capable due to adsorption to change the phase and energy interaction on the various boundary surfaces sections: liquid - air, liquid - solid, oil - water. Surface activity that is usual for majority organic compounds in certain circumstances can be determined by both their chemical structure, in particular, amphiphile (polarity and polarizability) of their molecules and external conditions: the nature of the environment and contacting phases, SAR concentration, temperature.

Usually surface-active reagents are organic compounds containing the hydrocarbon radical in the molecule and one or more polar groups.

According to the ionic characteristic all the surface-active reagents are usually divided into two large groups: non-ionic compounds that are not dissociated in ions during the process of their dissolution in water and ionic compounds. Depending on what kind of ions cause the surface activity of ionic substances, they are usually classified into: anionic SAR, cationic SAR and ampholytic SAR. Anionic surface-active reagents are more active in alkaline solutions, cationic reagents are in acid, ampholytic - in both.

According to solubility in water and oils, the surface-active reagents are divided into three groups: water-, water-oil - and oil-soluble.

The widest application in technologies of enhanced oil recovery was given to non-ionic surface-active reagents (NISAR).

This kind of SAR has more than 50 substances of different groups. The advantage of nonionic surface-active reagent (NISAR) is their compatibility with the waters of high mineralization and less adsorption in comparison with ionic reagents. However, many years of experience in the use of OP-10 surface-active reagent for enhanced oil recovery has not given any concrete results. About the efficiency of application of nonionic SAR as EOR method, there are different opinions, both positive and negative. The flooding method of SAR water solutions surfactants can be effectively used in strictly certain geological and physical conditions, that is proved by long-time experience (since 1971) of SAR application in Tatarstan for enhanced oil recovery of terrigenous Devonian deposits, and the use of SAR at the Samotlor field.

Numerous experimental researches, made by TatNIPIneft, have shown that the use of the concentrated solutions of SAR in primary oil displacement from the models of terrigenous rocks significantly improves the process of oil displacement. The maximum growth of displacement coefficient in comparison with water was 2.2% - 2.7%. Somewhat greater growth of displacement coefficient, equal to 3.5-4%, was obtained during the use of low-permeable porous medium models.

Among nonionic SAR the most widespread are OP-10, AF₉-4, AF₉-6, AF₉-10, AF₉-12, mainly due to their large volumes of industrial production. Ionic compounds of SAR are NCK, Sulfonal, NP-1, Azolyat A, B.

8.4. Polymer oil displacement.

Coefficient of mobility is the ratio of the relative permeability to the viscosity of the liquid. For oil and water the coefficients of mobility are the following:

, (8.3)

Darcy law for water and oil has the following view:

(8.4)

Water dynamic viscosity is several times less than oil viscosity. Consequently, more mobile, low-viscosity fluid (water) displaces more viscous, less mobile oil. When the oil is displaced by water, oil production decreases with the increase of the ratio of oil and water viscosities. To reduce this ratio polymer water solutions are used, for example, polyacrylamide (PAA), which has the capacity, even at low concentrations, to increase water viscosity significantly, to reduce its mobility and increase the displacement coefficient. The polymer molecule is a chain of atoms of carbon, hydrogen and nitrogen. The chain's length is comparable with the size of pores. Polymer molecules in water solution, moving along the pore channels, "cling" for the rock grains, creating an additional resistance and sorbing on the rock grains.

When the polymer water solution filtration that is a dilatant liquid, the Darcy law will be written in the form:

(8.4)

Where n<1, µ_bp- polymer water solution viscosity.

With the growth of the pressure differential the rate of polymer solution filtration increases at a lower value than if you filter pure water. figure 8.2, [7].

Fig. 8.2. The dependence of filtration rate of Newtonian (1) and dilatants (2) liquids on pressure differential (gradient)

There is a process of adsorption during the process of PAA water solution filtration that is similar with the properties of SAR. At low concentrations of PAA in water the quantity of sorbed substance corresponds to Henry isotherm (8.3).

PAA is released in the form of gel, solid granules or powder. The concentration of the PAA in water: by gel 1-5%, by solid polymer 0,08-0,4%. Due to high sorption of PAA the concentration of PAA should be brought to the value when the dynamic viscosity of water solution increases 5-6 times.

It is believed that water solution of PAA is useful when the oil viscosity is (10-30) mPa. In the result of PAA sorption by porous medium during the oil displacement there is formed the sorption front, as well as the oil displacement by water solutions of surfactants (SAR) (figure 6.1).PAA water solution is also used to control the development process of the formations with heterogeneous permeability on thickness. As the fluid is dilatants then high-permeable interlayers with the injected solution are watered out slower. When injection pressure increases then water displaces oil from low-permeable interlayers. Thus, the reservoir sweep flooding coefficient increases.

It is experimentally proved that with increasing polymer concentration the phase permeability of wetted phase decreases, but the permeability of hydrocarbon fluids increases at the same saturation.