Reasons for formation of low-resistivity oil saturated reservoirs
Analysis and synthesis of the reasons for low-resistivity oil and gas saturated reservoirs formation are carried out. This work allowed identifying two groups of geological cause-and-effect relations, which determine petrophysical and physical reasons for low-resistivity rocks occurrence. The prime mover is facies environment of sedimentation together with tectonic activity resulting in formation of channels for fluid migration. It is shown that in general the secondary geological reasons will always be a rock lithotype (four conductor types) determining film-bound water and electrically conductive minerals, or extension faults and fractures, which make a basis for imposed-epigenetic process resulting in additional surface conductivity. Both groups of geological relations cause an additional (surface) conductivity determined by the following factors: increase of inner area of pore and fracture surface of film-bound water in the rock and, thus, charge density; double electrical layer of clay fraction; interlaminar conductivity against electric charges in three-layer clay minerals; formation of electrically conductive minerals (pyrite) in the reservoir rock. In the case of anisotropy of electrically conductive clay partings in a bed, rock resistivity decreases with the increase of borehole inclination. Increased fracturing of a rock may cause its increased electric conductivity. Geological attributes of promising low-resistivity reservoirs are determined. The mentioned petrophysical reasons for the formation of rocks with higher electric conductivity (not accounted for in the course of well log data interpretation) are defined by the following physical principles: formation of surface electric circuit; increase of charge density; increase of charge mobility.
Key words: low-resistivity reservoir; hydrocarbons; oil and gas saturation; resistivity; well logging.
For citation: Mel’nik I.A. Reasons for formation of low-resistivity oil saturated reservoirs. Geologiya nefti i gaza. 2018;(6):129–136. DOI: 10.31087/0016-7894-2018-6-129-136.
2. Zubkov M. Yu. Crystallographic and litho-petrographic substantiation of electric behaviour of iron minerals, clay and terrigenous reservoirs (by the example of BV8 and JV1 beds in the Povkhovsky field). Gornye vedomosti. 2008;(11;12):20–32;30–53.
4. Leont'ev E.I., Malykhin A.Ya. et al. Abnormal electric conductivity of bound water and its influence on geophysical parameters. Osobennosti geologicheskogo stroeniya i neftenasyshchennosti produktivnykh gorizontov Zapadno-Sibirskoi nizmennosti : Tr. Tyumenskogo industrial'nogo instituta. – Tyumen' : Izd-vo TII, 1974. Issue 26. pp. 173–179.
6. Chikishev Yu.A., Kovaleva N.P., Reznichenko V.A., Shishkin R.A. Problem of delineation of structurally complex low-resistivity Jurassic reservoirs in the Kaimysovsky Arch. NTV OAO «NK «Rosneft'». 2008;(1):17–21.
7. Teploukhov V.M., Nakonechnyi A.V., Teploukhov A.V. Separation of a low-resistance facies and its impact on the geological model of the Yu1-1 layer of Shinginskoye field. Neftyanoe khozyaistvo. 2013;(6):85–87.
9. Gil'manova R.Kh., Egorov A.F., Krotov S.A., Ziyatdinov R.R. Oil and gas fields of Orenburg region illustrate application of methods specifying initial data to develop geological models. Neftepromyslovoe delo. 2012;(1):84–59.
10. Buller D. Old wells: delineation of pay sands in thin-bedded low-resistivity channel deposits. Neft', gaz i neftekhimiya za rubezhom. 1993;(1):26–32.
11. Vinogradov V.G. Cement composition in polymictic sandstone and siltstone: influence on resistivity. Osobennosti geologicheskogo stroeniya i neftenasyshchennosti produktivnykh gorizontov Zapadno-Sibirskoi nizmennosti : Tr. Tyumenskogo industrial'nogo instituta. Tyumen' : Izd-vo TII, 1974. Issue 26. pp. 185–189.
12. Kuz'michev O.B. A method of the nature assessment of complicatedly-built oil-saturated reservoirs, including low-resistant ones, in the fields of LLC "LUKOIL-Western Siberia". Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdenii. 2016;(11):26–32.
13. Komova A.D., D'yakonova T.F., Isakova T.G., Bata L.K., Kalugin A.A., Terent'ev V.Yu. Features of the structure and evaluation of oil saturation factor of low-resistivity upper Jurassic reservoirs on example of the Vat’egan field of Western Siberia. Ekspozitsiya Neft Gaz. 2016;53(7):17–21.
16. Cai Jun, Wu Hongshen, Guo Shusheng. Low Resistivity Pay Evaluation Using Triaxial Induction in Offshore South China. In: International Oil and Gas Conference and Exhibition in China. SPE, 2010.
17. Buzhuk L.A., Polivtsev A.V., Arkhipova L.D. Influence of reservoir rocks secondary transformations on electrophysical properties: the results of electron microscopy studies. Glubinnoe stroenie, geodinamika, teplovoe pole Zemli, interpretatsiya geofizicheskikh polei. Shestye nauchnye chteniya Yu.P. Bulashevicha : sb. mat-lov konferentsii. – Ekaterinburg: URO RAN; 2011. pp. 52–55.
19. Mel'nik I.A., Erofeev L.Ya. Physical-geochemical model of low-resistance collector and its practical application. Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdenii. 2014;(3):46–50.
21. Shevchenko S.M., Shevchenko V.N., Gubarev O.V., Bushkovskii A.P. Hypothesis of low-resistivity reservoir formation in the Katyl’ginsky field. Oborudovanie i tekhnologii dlya neftegazovogo kompleksa. 2008;(6):13–15.
22. Kozerenko S.V., Khramov D.A., Fadeev V.V. et al. Studies of pyrite formation mechanism in aqueous solutions at low temperature and pressure. Geokhimiya. 1995;(9):1553–1565.
23. Mel'nik I.A. Pyritization intensity as an indicator of the nature of the Jurassic formations saturation in Tomsk region. Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdenii. 2016;(3):41–49.
I.А. Mel’nik Scopus
School of Earth Sciences & Engineering of Federal Independent Educational Institution "National Research Tomsk Polytechnic University", Tomsk, Russia;