Properties of voids in the Senonian gaize of the northern part of West Siberia

This paper gives the very first description of the reservoir void spaces of the Senonian epoch, belonging to the area of Nadym, Pur and Tazovskiy in West Siberia. The research is based on the core analysis accomplished with such techniques as light microscopy, X-ray microtomography, and mercury porosimetry. The study has also employed the data received with volumetric and static analyzer of specific surface area and porosity of the samples. It has been found that fracture capacity amounts to 1/30 of total porosity, and flow channels are sized to a nanoscale, which depends on the form of silica prevailing in the formation.
Materials and methods
sThe following core analysis techniques have been applied and reviewed in order to solve the current problem: X-ray diffraction (XRD), thin section description, core microtomography, mercury porosimetry.
Results
Composition of argillous gaize reveals severalsections, which are distinctly different in the amount of various silica forms - quartz and OCT (opal, cristobalite, and tridymite). On the average, NB1 layer contains 22% of OCT and 44% of quartz, whereas NB2 shows 0.1% and 66% respectively. Major volume of reservoir void space is represented by West Siberan argillous gaize and connected to pores, while microfissure capacity is of minor nature, accounting for 1/30 of total porosity. This means that the reservoir belongs to porous fractured type of formation. Flow matrix channels of high OCT gaizes are significantly smaller than those in which silica is mostly represented by fine-grained quartz. Prevailing diameters are 10 and 100 nm for NB1 and NB2 respectively. Capacities of ultra-microcapillary pores, which are found in NB1 and NB2 gaizes and are less than 2 nm in diameter, do not differ. Thus, their sorption properties are nearly the same and yet equally poor. Further study of the void space of the gaize matrix with core flow digital services willenable to define the nature of difference of pore volume structure, as applicable to formationswith different OCT-content, which is essential for issues related to gas production from such reservoirs.
Сonclusions
Use of high-resolution scanning microscopy will also allow further research of void space structure at the level of subcapillary pores of less than 200 nm in diameter, which is required for evaluation of adsorption potential. As is known, the most effective micropore size to adsorb and hold occluded methane is about 0.8 nm. As Figure 8 suggests, NB1 and NB2 formations are alike in the volume of voids of less than 2 nm in diameter. Thus, theirsorption properties are nearly the same and yet equally poor. It therefore appears that gas in the gaizes is held by merely capillary force and not by chemical bond which is an important conclusion in the context of gas production.