DETERMINATION OF IMPLICIT OIL-AND-GAS-BEARING SAND INTERVALS BY STATISTICAL-CORRELATION INTERPRETATION OF GWS DATA

Abstract

Link for citation: Melnik I.A. Determination of implicit oil-and-gas-bearing sand intervals by statistical-correlation interpretation of GWS data. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 1, рр.54-63. In Rus. The relevance of the considered topic is related to the problem of searching for missed productive low-resistance sand intervals, the existence of which is caused by the presence of surface electrical conductivity in the pores of sandy rock. The purpose of this work is to illustrate briefly the results of using the technology of statistical-correlation interpretation of geophysical well logging in the search for implicitly missed low resistivity oil and gas reservoirs. Method. This paper briefly shows the method of statistical-correlation interpretation of well logging materials. Theoretical physico-chemical and formal-logical justifications of the method of statistical-correlation interpretation are presented. This method is based on the principles of correlation of measured and calculated geophysical and petrophysical parameters of the studied sand interval, which changes along the well are caused by dominant geochemical processes of superimposed epigenesis in a certain local interval in the territory of deep fluid penetration. The product of the approximation coefficient and the statistical interval parameter of two samples of measured characteristics corresponds to the statistical intensity of sand interval transformation processes. On the basis of a standard set of geophysical well logging data, using the method of statistical-correlation interpretation of well logs in sandy formations it is possible to determine the intensity of secondary processes such as pyritization, kaoliniteization, pelitization, carbonatization and formation of a double electric layer in clays, some of which may be the cause of an implicit decrease in the electrical resistivity of the rock. Certain boundary values of the intensities of these secondary processes may serve as an indicator of the presence of hydrocarbons in the studied formations. Results. The validity of the statistical-correlation method of well logging data interpretation was confirmed when comparing the results of calculating the intensities of transformation processes with the results of petrographic core analysis. By determining the intensities of mineral transformation processes affecting the increase in surface electrical conductivity of sandy rocks in the Nizhneluginetskaya well, promising Jurassic reservoirs were identified, which were confirmed by the results of core alcohol-benzene extraction. In the Vakh field, the results of identifying promising Cretaceous reservoirs on the basis of the use of technology of statistical-correlation interpretation of logging data were confirmed by the results of formation tests. In the previously missed sand interval oil was obtained. And, secondary carbonatization was an indicator of the presence of hydrocarbons with a probability of 80 %. Conclusions. If we use well logging data (both old and new fund) to calculate the intensity of geochemical processes as an indicator of the presence of hydrocarbons and the boundary values of these intensities in the sandy formations, it is possible with ~80 % probability to reveal the implicitly missed low-resistance oil and gas reservoirs.

Keywords

• Low-ohmic reservoir
• geophysical well surveys
• hydrocarbons
• secondary processes
• superimposed epigenesis
• missed oil deposits