8.5. Micellar-polymer flooding method.

The method of complex stimulation on oil reservoir by injection of surfactants mixture, alcohols,oil solvents, water solution of PAA and water is called a method of micellar flooding. When the solution contains the surfactant concentrations above critical to form micelle then the surfactant is in the form of clots (micelles) in the solution, which are able to absorb liquids that are the components of their inner phase. When the concentration of surfactants is high they can create oil-water aggregates together with oil and water – micella of the size 10^-510^-6 mm.

Outwardly the micellar solutions are transparent or translucent liquids that refer to the Newtonian liquids [1].

.

Micellar solutions with water external phase are well-miscible with water.

When relatively small amounts of hydrocarbons – oil solvents - alcohols, sulphides or other surfactants are used on the contact of complex solution - oil there is formed an area of complete oil mixing oil with this solution, on the contact oil - solution the surface tension sharply decreases. There is an area of low surface tension between water and oil. The further you are from the contact (displacement front) in the direction of injection wells then the water share in the solution is higher, until it turns into pure water.

Near the injection line the solution transfers into water, the viscosity of which is less than the viscosity of the solution. In this case, less viscous liquid (water) must force out more viscous (micellar solution). The displacement coefficient decreases. Thus, to push micellar solution on the polymer water solution is used. This kind of reservoir stimulation is called micellar-polymer flooding method. In practice the micellar solution bank is pushed into the reservoir by water, thickened by polymers. The minimum amount of the banks should be 4-5% of the pores’ volume of the worked up area.

According to the laboratory data the micellar solutions can displace up to 50-60% of the oil, remaining after the regular flooding implementation.

The compositions of the micellar solutions are different, for example, sultanates-6%,surfactants OP-4-1.2 %, isopropyl alcohol - 1,2%, kerosene - 51,6%, water - 40%. Or sulfonate-8%, surfactants OP-4 -2%, oil and hydrocarbons (C₅₊ )-30%, water - 60%.

8.6. Conformance change or control (straightening the injectivity profile) (cc)

Conformance change or control of the injection wells is sometimes called diverter technologies that is not correct from our point of view, since the flow direction of the injected water can stay unchangeable. But the increase of the injectability interval, where the injected water comes, occurs. Or it should happen if the chemicals are chosen in a correct way and reliable geophysical data about the injectability interval are given.

The formation consisting of several interlayers of different permeability and thickness, due to the compartmentalization, is developed unevenly, Kazemi or Serra model, Chapter 4, paragraph 4.2.3. Oil displacement occurs in high- permeability (HP) interlayers and, consequently, rapid flooding of the output happens. Low-permeability interlayers practically do not work, oil is not displaced from them. To isolate, cut high-permeability interlayers with larger diameter pore channels is necessary to inject specially selected chemical solutions, which are able to penetrate into the pore space of these channels. The size of molecules of the selected chemical compounds is comparable to the size of the channels of high permeability.

Under the influence of temperature and interaction with the surface of pore channels they form a viscous immovable or not mobile substance that is almost immovable and doesn’t give water an opportunity to move when the injection well bottomhole pressure increases. This solution does not penetrate into low-permeability channels. With the further injection the water begins to flow into the reservoir with low filtration properties and oil displacement from the interlayers that have not been previously covered by water flooding starts. Thus, the sweep efficiency increases and, consequently, oil recovery becomes higher.

а) б)

Fig. 8.4. The scheme of injectivity profile change. а) h₁ – high-permeability interlayer thickness before the technology implementation, б) h₂ , h₃ - low-permeability interlayers’ thickness after high-permeability interlayer isolation.

At the Samotlor field the wide application of CC technologies began in 1995. For the whole period of development, the accumulated volume of the additional oil production with the help of CC methods is 14 million tones. However, in general on the field, the efficiency is decreasing. In some cases the use of the same technologies provides absolutely opposite results.

Over the past years at the Samotlor field there have been implemented more than 90 various compositions of CC method. The spectrum of the used compositions by their physical and chemical properties (strength and resistance to destruction) has already adapted to thermobaric conditions of the formations, but the approaches to the choice of the areas, sequence of well stimulation, injectability volume determination, periodicity of the works, the selection of the reagents’ composition depending on geological conditions of formations require further improvement.

The used chemicals are divided into three main composition types: dispersed -based on the principle of the dispersed phase dominance; deposition-gel-forming solutions are the solutions that form gels or depositions; and complex compositions consisting, for example, of the gel-and-deposition-forming compositions, as well as of the gel-forming mixtures and dispersed compounds. Complex structures consider a combination of (injection) in a definite sequence of separate compositions that are different in their rheological and dispersed properties; their main aim is the complex influence on the near and remote areas of the reservoir.

Depending on the geological structure and the chosen system of the wells’ pattern the flow-to-clean-up intensity should be 1.5-2 per valid injection well per year.

Table 8.1. The types of chemicals’ compositions, applied at the Samotlor field.

Dispersed compositions			Deposition-gel-forming compositions			Complex compositions
DS, KDCGS, TGS, LDS, MAT, ODMS, TU			OS, ODS, KS-2, PDS, PDK, TcshSPK, GeO, VUG, BP-92			GeOS, GeOS+ON1, PDS+GeOS, PDS+ON2, DS+GeO, DS+OS, DS+KS-2, DS+EDS

It should be noticed that the above-mentioned types of compositions do not cover all the used reagents range in oil industry. To change the injectability profile and to increase the inflow profile the biological substances also can be used.