Lithological and Geochemical Heterogeneity of the Organo-Mineral Matrix in Carbonate-Rich Shales

Abstract

The paper discusses the issues of interaction of the organic matter and the siliceous-carbonate mineral matrix in unconventional reservoirs of the Upper Devonian Domanik Formation of the Upper Kama Depression of the Volga-Ural Basin. The Domanik Formation is composed of organic-rich low-permeability rocks. Lithological and geochemical peculiarities of rocks were studied using light microscopy, X-ray diffraction analysis (XRD), scanning electronic microscopy (SEM), and evaporation method. Organic matter was examined by the Rock-Eval pyrolysis with quantitative and qualitative evaluation of generation potential and maturity degree. Integrated analysis of results of lithological and geochemical studies allowed identifying intervals in the studied section where organic matter can form a complex association with the siliceous-carbonate matrix. It was fixed experimentally that in some cases the mineral carbonate matrix and the organic matter form a one-whole high-molecular compound. The authors supposed that in the course of sedimentation, organic matter is immobilized into the structure of the mineral carbonate matrix. At the deposition and diagenesis stage, the carbonate matter interacts with acids of the organic matter and forms natural organo-mineral polymers. Special physicochemical properties of such organo-mineral associations shed new light onto the problems of producing from hard-to-develop nonconventional carbonate reservoirs and evaluating the associated risks.

Alterations of Carbonate Mineral Matrix and Kerogen Micro-Structure in Domanik Organic-Rich Shale during Anhydrous Pyrolysis

“…According to pyrolytic studies, the DF refers to mature oil-producing rocks [38]. The DF shales are characterized by extremely low permeability and porosity (0.66 to 1.87), fractures and cavities in carbonate mineral matrix, inter-and intraparticle pores predominantly in the carbonate mineral matrix, and pores in the organo-mineral part of the rock [10,39,40]. The Domanik Formation is often considered as an analogue of the Eagle Ford Formation [32,41].…”

Application of X-ray Diffraction (XRD) and Rock–Eval Analysis for the Evaluation of Middle Eastern Petroleum Source Rock

“…Different authors have shown how geochemical trends allow scientists to improve the productivity evaluation of the formation [9]. Integrated lithological and geochemical studies allow scientists to identifying intervals, where organic matter can form in association with the siliceous-carbonate matrix [10,11] Rock-Eval methods are usually used as quick, inexpensive, and reliable screening options for source rock/reservoir rock characterization. There could only be occasionally available geochemical results due to the limitations and utility.…”

A Summary of “Petrophysics and Geochemistry of Unconventional Reservoirs”

“…Much attention is paid to the study of the kerogen chemical structure [7], variation of kerogen type on the depth [8], the interaction of the organic matter and mineral matrix [9], void space [10], and the kerogen-related multiscale heterogeneity and anisotropy [11] of the Bazhenov formation sediments.…”

“…Bogdanovich et al [9] discuss the issues of interaction of the organic matter and the siliceous-carbonate mineral matrix in organic-rich low-permeability rocks of the Upper Devonian Domanik Formation (Upper Kama Depression, Volga-Ural Basin, Russia). The authors identify intervals where organic matter can form a complex association with the siliceous-carbonate matrix using results of a complex study with light microscopy, X-ray diffraction analysis, scanning electronic microscopy, evaporation method, and the Rock-Eval pyrolysis.…”