Geochemical assessment of the Paleozoic hot shale in Ahnet Basin Algeria, and its implications in unconventional resource development.

Abstract

This study presents a comprehensive geochemical and geomechanical assessment of Frasnian shale from three wells situated in the Ahnet Basin, southwestern Algeria. Through Rock- Eval analysis and palynofacies examination, the Gas Ratio technique, the rock’s mechanical elastic properties, and mineralogical properties. The research explores the thermal maturity, organic richness, and hydrocarbon potential of the shale, while also shedding light on the depositional environment, sources of organic matter, and preservation conditions. At the same time, confirming these results by identifying the tendency, types, and contacts of hydrocarbon fluids. Also illuminating Brittleness indices through several methods. The findings offer a comprehensive understanding of the organic matter within the Frasnian shale, which could significantly boost the exploration and exploitation of unconventional resources in the region. In the first well, most samples revealed medium to excellent total organic carbon (TOC) content, but with limited potential hydrocarbons, indicating varying stages of gas-phase maturation. Conversely, the second well showed good to excellent TOC content with low hydrocarbons potential, indicating a more advanced stage of maturation, particularly within the dry gas phase. In contrast, the third well displays core samples rich in organic matter. However, both free and residual hydrocarbon potentials are low, suggesting potential for gas or dry gas. Microscopic analysis further confirmed the wells' maturity levels, with the organic material primarily originating from mixed marine Type II sources. Geomechanically, the first well exhibited the highest brittleness among the three wells, followed by the second well, while the third well showed the lowest values. These insights are crucial for assessing the hydrocarbon potential and maturation stages in the Ahnet Basin, as well as the rock brittleness potential for hydrofracturing and identifying optimal completion areas, or "sweet spots," making them essential for practical resource evaluation and exploitation. The evaluation results of wells X1, X2, and X3 concluded that X1 and X2 have better petroleum potential and fracking suitability than X3.