Samples of terrigenous rocks from producing Devonian reservoirs were investigated by us by physical and chemical methods. It was shown that content of held organic substance decreased with increase of clay minerals content in rock sample. Organic substance from clay containing rocks is depleted by light and middle fractions. It was stated that the most part (up to 70 per cent) of organic substance was not dissolved in organic solvents and was firmly associated with fine granulometric fractions of the rock where clay minerals were also concentrated. It was stated that a sample with lesser clay content contained greater content of organic substance when compared fine granulometric fractions of samples with various clay contents.
The quantitative determination of enthalpy of water wetting for rock samples by calorimetry was carried out. Wetting heat for standard samples decreases in the following order: montmorillonite > quartz > marble. Wetting heat of fine granulometric fractions is five times less than for quartz and ten times less than for montmorillonite (particle size is the same). And wetting heat of fine granulometric fractions from more clay rock sample is more than for the fractions from less clay samples.
The results of these investigations suggest about irreversible adsorption of oil components. It is conditioned by formation of clay-organic complexes. As a result of catalytic activity of clay minerals, insoluble organic substance is presented by condensed aromatic structures. Clay cement is distributed over sandstone in the form of films. In more clay rock samples only its part is hydrophobized by organic substance owing to reduced permeability of the rock.
The mechanism of oil migration in a reservoir and its extraction are determined in many respects by molecular-surface processes occurring at the phase boundary (rock forming minerals - fluids saturating a reservoir). A wettability is the important parameter characterizing a surface activity of oil-containing rocks. Among the minerals making up hydrocarbon-containing reservoirs, the hydrophilic ones predominate in natural conditions. The rock hydrophily decreases in the order: clays of hydromicaceous composition, furthermore, quartz, next are limestones, dolomites and feldspars. Adsorption interactions of reservoir rocks with oil and primarily with asphaltenes and tars are determined by a value of a rock specific surface, molecular-surface properties of minerals in their composition, an availability of bound water and other factors. Some facts of irreversible change of clay minerals under the action heavy hydrocarbon oil components adsorbed at their surface were described in [1].
Chemical properties of a rock surface are governed by structural hydroxyl groups represented schematically as:
Figure (1) (Available in full paper)
Silicon-oxygen fragments of rocks containing structural --- (OH) --- groups are responsible for acidic properties of a surface. The presence of isomorphous aluminium in the mineral silicate structure causes the formation of active centers' of another character. The presence of aluminium atoms in silicon-oxygen tetrahedrons at the sites of isomorphically substituted silicon, as shown in [2]:
Figure (2) (Available in full paper)
