Труды российских конференций

Clay minerals are widespread in hydrocarbon collectors. Being located on grain surface in pore space in the form of films, plates and bridges, clay minerals have big specific surface area and high adsorption capacity. The capability to adsorb hydrocarbons results in formation of adsorption-connate oil. Adsorption-connate oil stimulates the formation of film oil, changes the pore surface wettability from water-wet to oil-wet and, finally, effects oil recovery. (N.N. Mikhailov, 1992)

Clay minerals – aluminosilicates are situated in the rock in the form of fines less than 1 µm. The adsorption active centers are presented by surface charges. The surface charges are formed on the corners and ribs of crystal lattice and when the lattice ions are replaced by less charged ions. Exchangeable cations also act as adsorption cations. In the clay rocks the adsorption of ions from solution to surface is possible due to Van der Waals forces of attraction and electrostatic forces. These forces are induced when adsorbable ions polarize surface atoms. The OH groups also participate in active centre generation. OH groups are included in the crystal lattices of majority of clay minerals. OH groups under certain conditions can exchange their hydrogen for metal ions (cations).Thus a big amount of adsorption centers are formed on the rock surface. The excess of ions or surface charge of one sign induces attraction or appropriate ion´s orientation and water dipoles and other polar substances of the opposite sign. (Y. I. Tarasevich, F.D. Ovcharenko, 1975).

Dispersion and exchange capacity were investigated on core plugs from Novy Urengoy reservoir. Exchange capacity of clay fraction changed from 51 meq/100g to 94 meq/100g of rock. That means that the rock samples contained clay minerals such as montmorillonite and mixed-layer chlorite –illite constitution. This statement was proved by means ofX-ray diffraction analysis and thermal analysis. Clay minerals content changed from 0.8% to 1.5%. Specific surface was equal to 0.16-0.59 m2/g. Hydration numbers of exchangeable cations changed from 3 to 8, i.e. Na and Ca were the exchangeable cations here.

After that the cores were treated by different hydrocarbons and the effect of clay component on adsorption-connate oil was investigated.

It was stated that:

Adsorption-connate oil formed by different hydrocarbons in pore space of investigated cores in average equal (% to the total volume): by hexamethylene – 0.7; by hexane – 0.8; iso-octane – 0.8; by heptanes – 0.9; by decane – 1.9; by condensate – 6.7; by kerosene – 15.6; by diesel fuel – 19.2

Hydrocarbon adsorption depends on content of rock particles less than 1 µm. The larger the particle content (the more the content of clay minerals – aluminosilicates) – the higher the adsorption level.

Hydrocarbon adsorption depends on specific surface area. The bigger the specific surface area (the higher the clay mineral dispersion) – the higher is the adsorption level.

4. Hydrocarbon adsorption depends on exchange capacity of clay fraction. The higher the exchange capacity – the lower the hydrocarbon adsorption. In the given rock mixed-layer chlorite –illite constitution has the highest adsorption activity.

N.N. Mikhailov: – Residual oil saturation of producing reservoirs- Moscow, Nedra, 1992, p. 270.

Y. I. Tarasevich, F.D. Ovcharenko: – Adsorption on clay minerals – "Naukova Dumka", Kiev, 1975, p. 109.