Geochemical, Mineralogical, and Spectral Analysis of Oil Shale Deposits at Wadi Ashallala in Northeastern Irbid, Jordan

Technical Summary: Geochemical, Mineralogical, and Spectral Analysis of Oil Shale Deposits at Wadi Ashallala in Northeastern Irbid, Jordan

Problem Statement
Oil shale represents a critical energy resource for Jordan, with estimated reserves exceeding 70 billion metric tons. However, traditional methods for characterizing these deposits—such as the Fischer assay and Rock-Eval pyrolysis—are often expensive, time-consuming, and resource-intensive. While reflectance spectroscopy offers a rapid, non-destructive, and cost-effective alternative for identifying mineralogical and organic components, its application in Jordanian oil shale studies remains limited. Furthermore, no previous study had integrated geochemical, mineralogical, and spectral characterization approaches specifically for the oil shale occurrences in the Wadi al-Shallala region of northeastern Irbid. This study addresses this gap by providing a comprehensive analysis of these deposits to better understand their composition, origin, and resource potential.

Methodology
The research focused on oil shale samples collected from two locations: Wadi Kharja and Al-Wehdah, situated approximately 13 km and 20 km northeast of Irbid city, respectively. These sites are part of the Wadi Al-Shallala Chalk Formation (WSC) and the Muwaqqar Chalk Marl (MCM) within the Balqa Group.

The study employed a multi-analytical approach:

1. Geochemical Analysis:
   • Organic: Rock-Eval pyrolysis was conducted at APT Company (Oslo, Norway) to determine Total Organic Carbon (TOC), S1 (free hydrocarbons), S2 (pyrolysis hydrocarbons), S3 (oxygen index), Tmax, Hydrogen Index (HI), Oxygen Index (OI), Production Index (PI), and Genetic Potential (GP).
   • Inorganic: X-ray Fluorescence (XRF) using an EDXRF system (NEX QC+ QuantEZ) was utilized to quantify major oxides (CaO, SiO2, P2O5, Al2O3, SO3, etc.).
2. Mineralogical Analysis:
   • X-Ray Diffraction (XRD): Performed using a Rigaku Ultima IV Powder Diffractometer to identify crystalline phases.
   • Fourier Transform Infrared (FTIR): Conducted using an ALPHA FTIR Spectrometer (400–4000 cm⁻¹ range) to identify functional groups in organic and inorganic materials.
3. Spectral Analysis:
   • Reflectance Spectroscopy: Laboratory measurements were taken using an Analytical Spectral Devices (ASD) Field Spec 4 spectroradiometer (0.35–2.5 µm range). Data processing included continuum removal to normalize spectra and isolate diagnostic absorption features.

Key Results

• Geochemical Characteristics:
  • TOC: Values ranged from 0.44% to 19.70%. The Al-Wehdah section generally exhibited lower TOC values (mostly <6%) compared to Wadi Kharja.
  • Kerogen Type: The majority of samples were classified as Type I kerogen (lipid-rich, derived from algae/plankton), with some Type II present. This was evidenced by high Hydrogen Index (HI) values (ranging from 51 to 806 mg HC/g TOC) and S2 values.
  • Thermal Maturity: Tmax values ranged from 412°C to 437°C, and Production Index (PI) values were below 0.1. These indicators confirm that the source rocks are thermally immature.
  • Hydrocarbon Origin: S1 vs. TOC plots indicated indigenous (autochthonous) hydrocarbons with no evidence of migration.
• Mineralogical Composition:
  • XRD: Calcite was the predominant mineral phase in both locations. Minor amounts of quartz, montmorillonite, kaolinite (notably in Wadi Kharja sample 9), dolomite, and gypsum were identified.
  • XRF: Calcium oxide (CaO) was the most abundant oxide (averaging 68.9% in Wadi Kharja and 71.92% in Al-Wehdah), followed by Silicon dioxide (SiO2) at an average of 10.8%.
• Spectral Signatures:
  • FTIR: Identified hydroxyl groups (3399/3397 cm⁻¹), kaolinite (3600 cm⁻¹), saturated C-H bonds (2925 cm⁻¹), carbonate vibrations (2513, 1424, 875 cm⁻¹), and carbonyl groups (1796 cm⁻¹).
  • ASD Reflectance: Diagnostic absorption features were observed at 1.40 µm and 1.90 µm (hydroxyl/water), 1.70 µm (organic compounds/C-H overtones), 2.20 µm (clay minerals/Al-OH), and 2.30 µm (carbonates).

Significance and Claims
The authors assert that this study provides a valuable baseline for understanding the composition and resource potential of oil shale in the Wadi al-Shallala region. By integrating spectral data with traditional geochemical and mineralogical analyses, the study demonstrates that reflectance spectroscopy can effectively identify key constituents such as carbonates, clays, and organic compounds.

The paper claims that the methodologies employed are beneficial for:

• Enhancing the accuracy of hydrocarbon resource assessments in arid and semi-arid environments.
• Contributing to the development of spectral libraries specific to Jordanian oil shale deposits.
• Supporting future mineral exploration, environmental monitoring, and sustainable resource management strategies in Jordan.

The authors note that while the study offers significant insights, future work should focus on integrating these laboratory spectral measurements with high-resolution satellite imagery and machine learning to develop more reliable predictive models for oil yield and sulfur content. The study modestly positions itself as a step toward optimizing resource assessment techniques beyond traditional, costly methods.