Abstract
In this study, collected samples of nine different wells from the Middle East are used for various geochemical analyses to determine the hydrocarbon generation potential. The determination is carried out following the grain density, specific surface area, XRD, and Rock–Eval pyrolysis analyses. Four different types of kerogen are plotted based on the Rock–Eval analysis result. Kerogen type I usually has high hydrogen index (e.g., HI > 700) and low oxygen index, which is considered oil-bearing. Kerogen Type II has hydrogen index between type I and type II and oxygen index higher than type I (e.g., 350 < HI < 700) and is also considered to have oil-bearing potential. Kerogen type III has a lower hydrogen index (e.g., HI < 350) and is considered to have a primarily gas-generating potential with terrigenous organic matter origination. Kerogen type IV has a very low hydrogen index and higher oxygen index (compared with other types of kerogen), which is considered the inert organic matter. The kerogen quality of the analyzed samples can be considered as very good to fair; the TOC content ranges from 1.64 to 8.37 wt% with most of them containing between 2 and 4 wt%. The grain density of these examined samples is in the range of 2.3–2.63 g/cc. The TOC and density of the samples have an inversely proportional relationship whereas the TOC and the specific surface area (BET) has a positive correlation. The specific surface area (BET) of the examined samples is in the range of 1.97–9.94 m2/g. The examined samples are dominated by clay, primarily kaolinite and muscovite. Additionally, few samples have a higher proportion of quartz and calcite. The examined samples from the Middle East contain kerogen type III and IV. Only two samples (JF2-760 and SQ1-1340) contain type I and type II kerogen. Considering Tmax and Hydrogen Index (HI), all of the samples are considered immature to early mature. Rock–Eval (S2) and TOC plotting indicate that most of the samples have very poor source rock potential only with an exception of one (JF2-760), which has a fair-to-good source rock potential.
Highlights
Global interest is growing around shale and conventional gas resource availability and extraction due to energy transitions to low-carbon energy systems to limit global warming to below 2 °C
The total organic carbon (TOC) values of the examined samples range from 1.64% to 8.37% with most of the samples ranging between 1.6% to 3.5% (Table 4)
Kerogen has a lower density compared with others; the higher the TOC content, the lower is the density
Summary
Global interest is growing around shale and conventional gas resource availability and extraction due to energy transitions to low-carbon energy systems to limit global warming to below 2 °C. Investigations suggested that global shale gas availability would not make a significant (positive or negative) impact on the cost and feasibility of an energy system transition consistent with the goal, nor does it significantly affect the cost-optimal decarbonization pathway globally [1]. Organic matter evolves through different geochemical (diagenesis, catagenesis, and metagenesis) processes due to primarily increasing temperature. Thermogenic hydrocarbon (oil, condensate, and dry and wet gas) generates through the kerogen cracking at higher temperatures and pressure. Geochemists have explained dry gas generation primarily in two ways: direct kerogen yield and trapped oil secondary cracking. Rock–Eval pyrolysis allows the quantitative and qualitative evaluation of OM generation potential, migration, accumulation, and degree of maturity. Integrated lithological and geochemical studies allow scientists to identifying intervals, where organic matter can form in association with the siliceous-carbonate matrix [10,11]
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