The increasing global demand for energy has raised interest in unconventional hydrocarbon resources such as shale gas, tight oil, and coalbed methane. A major limitation in exploiting these resources is the insufficient level of thermal maturity of kerogen to generate producible hydrocarbons. The application of thermochemical fluids to accelerate kerogen maturation by generating in-situ heat and pressure was studied to test the ability to enhance hydrocarbon recovery from organic-rich shales. Experiments were conducted on organic-rich shale samples from a Jordanian oil shale. Thermochemical fluids composed of ammonium chloride and sodium nitrite were selected in this work, because they are reliable, provide a controlled heat reaction, and are relatively environmentally friendly. They were injected into shale samples using a core flooding system under high-pressure and high-temperature conditions. The chemicals used can increase the temperature up to 316°C and pressure up to 3100 psi (21.37 MPa). The rock properties were assessed before and after the thermochemical treatment. Rock-Eval pyrolysis, gas chromatography, X-ray diffraction, X-ray fluorescence, computed tomography scans, and elastic wave velocity measurements were performed to evaluate geochemical, petrophysical, and geomechanical changes. Results showed a reduction in total organic carbon from 12.9-15.7 wt.% down to 9.2-13.9 wt.% (18-42%) accompanied by an increase in free hydrocarbon volume from 1.8-2.2 mg/g to 3.6-4.2 mg/g (80-130%). These changes indicate effective kerogen conversion. Porosity increased by up to 20% with treatment effectiveness strongly controlled by pre-existing fractures that enhanced fluid penetration. Additionally, compression and shear velocity ratios and Poisson’s ratios increased by 8-30% and 5-24%, respectively, indicating a significant impact on geomechanical properties. Mineralogical and elemental compositions remained largely unaffected as indicated by the X-ray diffraction and X-ray fluorescence analyses. Ultimately, the effectiveness of thermochemical fluids depends on initial rock characteristics, with high total organic carbon and pre-existing fractures enhancing fluid penetration and treatment performance. Overall, the dual benefits of thermochemical fluids treatment in promoting kerogen thermal maturity and modifying the petrophysical and mechanical behavior of organic-rich shales were demonstrated in this study. By generating in-situ heat and pressure, thermochemical fluids promote kerogen maturation, increase porosity, and induce microfractures, thereby improving fluid mobility and hydrocarbon recovery. These improvements occur without altering the rock’s mineral or elemental composition. As a novel, energy-efficient alternative to conventional maturation methods, thermochemical offers a scalable and effective solution for unlocking unconventional resources while preserving long-term structural stability. • A novel method was developed to accelerate the maturation of immature organic-rich shales by using thermochemical fluid (TCF) injection. • The method reduced total organic carbon (TOC) by 18 to 42% and increased free hydrocarbon content (S1) by 80 to 130%. • Thermochemical maturation enhanced the shale core porosity by 10 to 20% due to the microfracture development and pore enlargement during the treatment. • Gas chromatography confirmed hydrocarbon generation, while XRD and XRF analyses showed minimal changes in the shale mineralogy and elemental composition. • TCF treatment significantly altered the shale geomechanical and petrophysical properties, with initial rock characteristics playing a key role in treatment effectiveness.
Moh-Ali et al. (Sun,) studied this question.