Experimental investigation of thermal decomposition of Bazhenov formation kerogen: Mechanism and application for thermal enhanced oil recovery

Abstract

Bazhenov formation is the key kerogen-bearing oil shale reserve in Russia. Therefore, as recovery from conventional reservoirs decreases, the need to find enhanced oil recovery (EOR) techniques in order to develop Bazhenov formation becomes evident. Despite the huge amount of reserves, oil shales in Russia have not been developed extensively due to the absence of suitable recovery technique. High pressure air injection (HPAI) is one of the recovery techniques that has a potential to become the main recovery method. In order to design this method correctly, different aspects must be investigated. To do that, thermal analysis methods should be implemented. In this work, thermomicroscopy, simultaneous thermal analysis and open system pyrolysis were performed to investigate kerogen conversion process.The optical thermomicroscopy showed changes in the macrostructure and the morphology of the Bazhenov shale sample during heating up to 720°C with the heating rate 10°C/min. It was demonstrated that the conversion of kerogen into hydrocarbons caused increasing in sample porosity. Geometrical characteristics of pores such as size and shape were determined, dynamic events during the heating were investigated. During the air purge, intensive fracturing occurred along the voids formed due to oxidation of organic matter at 450°C. The simultaneous thermal analysis (STA) revealed linear relationship between TOC and heat value for single well samples. Interval of oxidation reactions was determined.Bulk-kinetic parameters (activation energy and frequency factor) were calculated by numerical inversion of pyrolysis data using the Kinetics2015 optimization software. Fixing the A factor to a 2×1014s−1 and using a spacing of 1kcal/mole in the discrete activation energy distribution were investigated. In result, solution for different samples along the well was rather stable comparing to traditional approach.