Analysis of dependence of porosity of Lower Cretaceous reservoirs of the Tersko-Sunzhenskaya oil and gas bearing area on petrophysical parameters

Abstract

Relevance. Deep terrigenous reservoirs account for more than 50% of oil and gas deposits. However, these reservoirs are characterized by high clay content, low porosity and high heterogeneity. Nevertheless, the Lower Cretaceous Alb-Aptian reservoirs in the studied area are currently the most promising, but require more in-depth study. The nature of clay particles distribution in reservoir rocks is one of the key problems for the interpreter due to their rather ambiguous influence on reservoir quality. Therefore, the content of clayey, siltstone particles in the reservoir complicates the determination and evaluation of petrophysical parameters of productive strata. Accordingly, analysis of the type, content and mode of clay content distribution in the reservoir is important to assess the oil and gas content of the reservoir. The article contains the results of petrophysical analysis of cores from some wells that penetrated the Lower Cretaceous terrigenous sediments of the Tersko-Sunzhenskaya oil and gas bearing area. Dependence of porosity by impregnation on other petrophysical parameters (clay content, carbonateness, density, total fraction of clay, carbonate and terrigenous substances) was reviewed for the whole set of the corresponding parameters. Purpose of the study. To obtain dependences of saturation porosity on carbonateness, siltstone fraction and clay content, in order to evaluate the influence of petrophysical parameters on the reservoir properties of terrigenous deposits of the Lower Cretaceous. Methodology of the study. The results of laboratory analyses of cores of terrigenous Cretaceous sediments collected during the years of the study were used to establish pairwise relationships between porosity on the one hand, and the total parameter, which simultaneously takes into account the characteristics of terrigenous, carbonate and clay parts of the rock on the other hand. Results. The obtained dependences are given in tabular and graphical forms. The most stable of them can be applied for forecast calculations. Establishment of similar dependencies is recommended in all cases of mass core sampling during drilling, both for forecasting and for recognizing and checking anomalous results of petrographic parameters. Also, the results obtained can be used in the future in creating a three-dimensional model of the Lower Cretaceous deposit of the Tersko-Sunzhenskaya oil and gas bearing area.