Innovative approaches to study heterogeneous anisotropic reservoirs of Turonian deposits for reliable assessment of reservoir properties

UDK: 550.822.3

Key words: laboratory investigation of core, logging, heterogeneous anisotropic reservoir, the Turonian age deposits, X-ray tomography, triaxial induction logging

Authors: A.V. Malshakov, I.O. Oshnyakov, E.G. Kuznetsov (TNNC LLC, RF, Tyumen), O.A. Loznyuk, V.N. Surtaev, R.A. Shaybakov (Rosneft Oil Company PJSC, RF, Moscow)

The main explored oil and gas reserves in Western Siberia are associated with chalk and upper Jurassic deposits. Above-Cenomanian stratum is a complex object of study and is referred to hard-to-recover reserves of crude hydrocarbons, which cannot be effectively selected with the application of traditional development methods for geological and technological reasons. 

Despite the fact, that potential of Turonian deposits was proved by well testing on the many fields in the North of Western Siberia and that the given interval is considered as a development target, the reservoir properties of these deposits are not explored enough and its potential is not clear.  Structural and textural features of Turonian reservoir structures can be reasons for that, particularly, extra thin interbedding (bioturbation) of sandstones/ siltstones- shale interlayers, with a thickness of mm factions, so the heterogeneity is observed up to thin section scale.  Such textural feature can be the reason for significant uncertainties when studying the complex reservoir not only by logging methods, but also by laboratory studies of core samples, it determines the application of individual approaches to analyze core and log data to study heterogeneous anisotropic Turonian reservoirs. Much attention is given to reliable determination of the portion of permeable layers and reconstruction of its true properties based on the logging data interpretation. Methods of estimation reservoir properties including heterogeneous reservoir structure were considered.

Imaging of full-size core is presented in this work; it allows building 3D model of x-ray density of full-size core. The processing procedure of 3D x-ray tomography of full-size core is presented; it allows estimating the vertical portion of the permeable component of anisotropic reservoir (NTG). Estimation results of portion of the permeable component of heterogeneous anisotropic reservoir (NTG) are presented on the basis of special logging complex methods, particularly, on the basis of formation micro imager and triaxial induction logging. The triaxial induction logging was also used to estimate electrical resistance anisotropy of studied reservoirs and allowed estimating electrical resistance of permeable variations. Results of evaluation of the reservoir gas saturation coefficient were achieved by the specific interpretation of triaxial IRR and better correlated with well testing results. 

Ignoring the textural heterogeneity of the deposits considering anisotropy of its physical properties can cause undervaluation of the resource potential of Turonian deposits. Whereas, the petrophysical assessments of anisotropic reservoir model improve the reliability of evaluation of hydrocarbons reserves, optimize geological and hydrodynamic modeling, increase prediction validity of gas recovery factor.
References
1. O.A. Loznyuk, V.N. Surtaev, R.A. Shaybakov et al., Development of gas deposits
in the Turonian low-permeability reservoirs (In Russ.), Neftyanoe
khozyaystvo = Oil Industry, 2015, no. 11, pp. 46–51.
2. Loznyuk O.A., Surtaev V.N., Sakhan' A.V. et al., A multistage stimulation operation
to unlock the gas potential of the Turonian siltstone formation in Western
Siberia (In Russ.), SPE 176706, 2015.
3. Bekirova I.P., Agalakov S.E., Rozbaeva G.L., Dubrovina L.A., Perspektivy
neftegazonosnosti nadsenomanskikh otlozheniy na Bol’shekhetskom proekte
i prilegayushchikh territoriyakh (Prospects for oil and gas potential of Above-
Cenomanian deposits in the Bolshekhetsky project and surrounding areas),
Proceedings of scientific and practical conference “Puti realizatsii neftegazovogo
potentsiala KhMAO” (Ways of realization of oil and gas potential of
KhMAO): edited by Volkov V.A., Khanty-Mansiysk, 2015, pp. 156–164.
4. Kharitonov V.M., Marinov V.A., Ivanov A.V., Fomin V.A., Verkhnemelovye inotseramy
skvazhinnykh razrezov Zapadno-Sibirskoy nizmennosti i nekotorye
voprosy stratigrafii turonskogo yarusa (Upper Cretaceous inoceramus of the
well section of the West Siberian Plain and some questions of the stratigraphy
of the Turonian stage), Izvestiya Saratovskogo universiteta. Novaya seriya.
Seriya Nauki o Zemle, 2007, V. 7, no. 2, pp. 61–71.
5. Reshenie V Mezhvedomstvennogo regional’nogo stratigraficheskogo
soveshchaniya po mezozoyskim otlozheniyam Zapadno-Sibirskoy ravniny (Decisions
of the 5th interagency regional stratigraphic meeting on Mesozoic sediments
of the West Siberian Plain), Tyumen’: Publ. of ZapSibNIGNI, 1991, 54 p.
6. Zhemchugova V.A., Berbenev M.O., Naumchev Yu.V., New seismic technologies
for better field exploration (Case study of upper cretaceous reservoirs
in West Siberia) (In Russ.), Tekhnologii seysmorazvedki, 2015, no. 3,
pp. 80–88.
7. Serra O., Andreani M., Thin beds – A guide to interpretation of thinly layered
reservoirs, Schumberger, 1991, 82 p.
8. Svikhnushin N., Tukhtaev R., Shmyglya K., Studying thin layer reservoirs. New
technologies (In Russ.), Neftegazovoe obozrenie = Oilfield Review, 2002, Autumn,
pp. 46–51.
9. Martynov M.E., Kozlov A.V., Leskin F.Yu., Successful application of special log
interpretation methodology for estimation of petrophysical properties of thinbedded
reservoirs of Vikulovskaya layers of Krasnoleninskoe oilfield (In Russ.),
SPE 166831, 2013.
10. Barber T., Anderson B., Abubaker A. et al., Determining formation resistivity
anisotropy in the presence of invasion, SPE 90526, 2004.
11. Klein J.D. et al., The petrophysics of electrically anisotropic reservoirs, The
Log Analyst, 1997, V. 38, no. 3, pp. 25–36.