Geochemical and petrophysical characterization of the Midra Shale, Qatar

Shale gas is considered one of the promising unconventional gas reservoirs that would help meet the current demand for natural gas as a clean energy resource. Qatar has several shale gas reservoirs from diverse epochs, including the Eocene Midra Shale. Outcrop samples of Midra Shale were collected from the Umm Bab and Dukhan areas, and multiple measuring and geochemical analysis techniques were utilized to characterize the mineralogy, microstructure, and pores type. X-ray diffraction (XRD) mineralogy analysis and X-ray Fluorescence (XRF) indicated that palygorskite is the dominant clay in Midra Shale. The mineralogy of Midra Shale includes other minor minerals such as calcite, quartz, and halite, as well as low content of other clays, including sepiolite, smectite, and illite. Although the Midra Shale contains many elements, such as shark teeth and large foraminifera that support deposition under marine conditions, the existence horizons of laminated shale designate mixed marine continental depositional settings. Scanning electron microscope (SEM) images revealed various types of pores in Midra Shale, such as intragranular, intergranular, and organic pores. The geochemical analysis revealed that the Dukhan section is poor in organic matter and has low potential as a source rock for oil or gas. In contrast, the Umm Bab Section has a relatively high amount of organic carbon, making it a potential source rock.