Characterization of Pore Structure and Fluid Saturation of Organic-Rich Rocks Using the Set of Advanced Laboratory Methods

Abstract

The global shift in energy reserves structure, including Russia, is moving towards the effective development of unconventional oil and gas reservoirs (EIA 2013). However, the problem of assessing hard-to-recover reserves in low-permeability, organic-rich reservoirs still lacks a comprehensive solution. This is primarily due to the lithological, physicochemical, and reservoir properties of the rocks, and often results from the utilization of a limited set of laboratory techniques that yield different values for the same measured property. Several studies on various aspects of unconventional reservoirs also emphasize the necessity of employing alternative techniques for laboratory analysis of core samples (Handwerger et al. 2012; Yuan et al. 2019; Curtis et al. 2012). Currently, the depletion of oil and gas reserves in traditional sandy reservoirs has made the search for new hydrocarbon deposits increasingly important. A significant area of focus in this regard is the study of potentially productive intervals within unpromising kerogen-clay-siliceous strata that are rich in organic content. One notable example of such intervals is the high-carbon Bazhenov formation in West Siberia (Ulmishek et al. 2003; Kontorovich et al. 1997). Modern field development methods, such as hydraulic fracturing (HF), the use of organic solvents, and thermal recovery, have enabled increased production from high-carbon formations with low reservoir properties. However, in order to make accurate predictions for the development of high-carbon formations using modern methods, it is crucial to accurately describe the complex void space system and understand the relationship between hydrocarbon compounds, water, and the solid rock matrix. Otherwise, it is impossible to predict the behavior of the void space following anthropogenic interventions using modern field development techniques. To date, several methodological recommendations and approaches have been developed for assessing oil resources and calculating reserves in Bazhenov formation deposits (Bilibin et al. 2015; Petersilye, Komar, et al. 2016; Prishchepa et al. 2015). However, these methodological recommendations should be carefully adjusted depending on the type of formation, the degree of organic matter (OM) transformation in high-carbon formations, and other factors. Factors such as macro- and microlithological characteristics of the section, mineral composition, reservoir properties, type, maturity, and amount of OM in the rock, morphology of the pore space and its hydrocarbon (HC) filling, the presence of free and bound water, and wettability, among others, should be initially included in the fluid dynamic model. These factors form the basis for refining existing methodological recommendations.