The study of water saturation process of dolomite core under atmospheric pressure by MRI method

P.P. Kobchikova^a*, M.M. Doroginitskii^a**, A.V. Fattakhov^a***, V.E. Kosarev^a****, V.M. Murzakaev^a*****

^aKazan Federal University, Kazan, 420008 Russia

^b“TNG-Group” Ltd, Bugulma, 423236 Russia

E-mail: ^*pollymoon@ya.ru, ^**m_dorogin@bk.ru, ^***avfattahov@kpfu.ru, ^****victor.kosarev@kpfu.ru, ^***** murza@tngf.tatneft.ru

Received September 26, 2017

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Abstract

The distribution of the fluid content in the process of water saturation of fine-grained full-sized dolomite core has been measured by magnetic resonance imaging (MRI). Two stages have been allocated in the saturation process. A rapid growth (up to 5 min) of the fluid content in the near-surface core layer (~ 0.5 cm) to the maximum saturation has been observed at the first “hydrodynamic” stage of the process. The hydrodynamic stage of fluid saturation with a void rock space has been considered in the framework of the Darcy filtration model. The pressure gradient in this model has been determined by the difference between the pressure of the fluid formed from the hydrostatic and capillary pressure and the increasing pressure of the compressed gas (air) in the confined pore space. At the second, “diffusion”, stage (from 5 to 320 min), the slow growth of the water content profile has been observed in the central part of the core compared to the hydrodynamic stage. The diffusion stage of saturation has been considered within the model of equilibrium of fluid and gas pressures. The mass transfer of the fluid is carried out at the expense of the fluid content gradient.

Keywords: water saturation, porous space, dolomite core, magnetic resonance imaging, diffusion in porous space

Acknowledgments. We thank V.D. Skirda, Professor of Kazan Federal University, for the opportunity to perform measurements with a MRI scanner. We are especially grateful to D.L. Mel'nikova, postgraduate student, for her help during the measurement procedure.

The study was supported by the Ministry of Education and Science of the Russian Federation (project no. 02.G25.31.0131).

Figure Captions

Fig. 1. On the left – photos of the studied fragment of the full-sized dolomite core; on the right – MR images of the dolomite core in the sagittal and transversal projection.

Fig. 2. Transversal MR images of the core obtained at different stages of the saturation process: on the left – at the beginning of water saturation; on the right – at the final stage of water saturation; wite spots on MR images – calibration phantoms.

Fig. 3. On the left – MRI intensity digitization: A) in the area of core saturation in the selected radial direction; B) in the area of noise. On the right – MRI intensity profiles: C) in the area of saturation I_s (r); D) in the area of noise I_n (r).

Fig. 4. The profiles of relative volumetric moisture content in the dolomite core sample at the first stage of saturation.

Fig. 5. The profiles of relative volumetric moisture content in the dolomite core sample at the second stage of saturation.

Fig. 6. Changes in the relative volumetric fluid content in the subsurface layer w (R, t) and in the central part of the core w (0, t). Saturation time point t_c ~ 5 min divides two different stages in the behavior of relative volumetric moisture content.

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For citation: Kobchikova P.P., Doroginitskii M.M., Fattakhov A.V., Kosarev V.E., Murzakaev V.M. The study of water saturation process of dolomite core under atmospheric pressure by MRI method. Uchenye Zapiski Kazanskogo Universiteta. Seriya Estestvennye Nauki, 2017, vol. 159, no. 4, pp. 618–628. (In Russian)

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