Shadrina info 6-2019 | oilandgasgeology

Якорь 1

S.V. Shadrina, U.Yu. Azarapina, A.A. Shadrin, I.L. Kritskii

Formation of interstitial space in serpentinite

DOI 10.31087/0016-7894-2019-6-41-46

The paper presents the results of investigations of mineral, chemical composition and porosity of serpentinite and altered serpentinite (metasomatic rocks). It is found that porosity factor and pore size in serpentinite are secondary to morphologic varieties of serpentine – antigorite to lizardite ratio. In metasomatites (carbonate, siliceous-carbonate, and talc-carbonate rocks) – alterations of serpentinite, and carbonated serpentinite, formation of pores is associated with replacement and coarsening of carbonate grains in the process of their recrystallization. Porosity increases when thin-flake serpentine (lizardite) content exceeds 10% and/or carbonate content exceeds 20 %. Thin-flake serpentinite with small pores (less than 0.005 mm) associated with the gas reservoir top is more porous that the large-flake serpentinite. The relationship between the rock material composition and porosity factor is noted; i.e., chemical composition of the rock (X-ray fluorescence analysis and gamma spectrometry data) in an integrated manner present all secondary alterations, which occurred in the rock; they also contain information on its porosity. Analysis of porosity as a function of its chemical composition is carried out using the machine learning methods. Five methods of different classes are used to create the predictive models of porosity, they are: Elastic Net Regression, Support Vector Regression, Multilayer Perceptron, Random Forest, and Extremely Randomized Trees. The highest reliability for relationship revealing is obtained using the Extremely Randomized Trees method providing an average coefficient of determination (R2) for test sets equal to 0.777; Pearson coefficient of correlation (r) is 0.887. Thin-flake and, respectively, fine-pore rock texture results in the increased chlorine and bromine because of good anion-exchange properties of serpentine: the larger surface, the more retained component. The studied serpentinite is a hydrocarbon reservoir in which their natural separation occurred. Oil and gas saturated intervals alternate in the section: oil hydrocarbons are found in foliated serpentinite, and gas hydrocarbons in a thin-flake one.

Key words: serpentinite; antigorite; lizardite; carbonate; porosity; chemical composition; machine learning methods.

For citation: Shadrina S.V., Azarapina U.Yu., Shadrin A.A., Kritskii I.L. Formation of interstitial space in serpentinite. Geologiya nefti i gaza. 2019;(6):41–46. DOI: 10.31087/0016-7894-2019-6-41-46.

References

1. Echarte M.E.P., Reguera J.L.C. Oil and Gas Exploration in Cuba: geological-structural cartography using potential fields and airborne gamma spectrometry. Springer, 2017. 88 p. DOI: 10.1007/978-3-319-56744-0.
2. Manuella F.C., Scribano V., Carbone S. Abyssal serpentinites as gigantic factories of marine salts and oil. Marine and Petroleum Geology. 2018;92:1041–1055. DOI: 10.1016/j.marpetgeo.2018.03.026.
3. Raznitsin Y.N. Geodynamics of ophiolites and formation of hydrocarbon fields on the shelf of eastern Sakhalin. Geotectonics. 2012;46(1):1–15.
4. Yurkova R.M., Voronin B.I. Role of geodynamic pair “island arc – trench” in formation of hydrocarbon and ore fields. In: Degazatsiya Zemli: geodinamika, geoflyuidy, neft', gaz i ikh paragenezy: sb. tr. Vseros. konf. (Moscow, 22–25, April, 2008). – Moscow: GEOS; 2008. pp. 554–556.
5. Shakirov R.B. Gasgeochemical fields of the Eastern Asia Marginal seas. Moscow: GEOS; 2019. 340 p.
6. Sokolov V.V., Mazarovich A.O. Gas hydrates in the sedimentary cover of passive oceanic margins: Possibilities of prediction based on satellite altimetry data in the Atlantic and Arctic. Lithology and Mineral Resources. 2009;44(5):441–450. DOI: 10.1134/S0024490209050034
7. Yurkova R.M., Voronin B.I. Transfer of hydrogen and methane molecules in serpentine structural cells in the course of ophiolite diapirintrusion. In: Degazatsiya Zemli: geodinamika, geoflyuidy, neft', gaz i ikh paragenezy: sb. tr. Vseros. konf. (Moscow, 18–22, April, 2010). Moscow: GEOS; 2010. pp. 232–251.
8. Kendrick M.A., Scambelluri M., Honda M., Phillips D. High abundances of noble gas and chlorine delivered to the mantle by serpentinite subduction. Nature Geoscience. 2011;4(11):807–812. DOI: 10.1038/ngeo1270.