Mud gas isotope logging application for sweet spot identification in an unconventional shale gas play: A case study from Jurassic carbonate source rocks in Jafurah Basin, Saudi Arabia

The Jafurah basin is a new frontier unconventional exploration play equivalent in size to the successful Eagle Ford play in south Texas. The basin is located immediately east of the adjacent supergiant Ghawar Oil Field. The middle to upper Jurassic organic-rich mudrocks are recognized as the source of Ghawar hydrocarbons and are being extensively evaluated across the Jafurah basin for shale gas potential. These source rocks, notably the Jubaila and Tuwaiq Mountain, and to lesser extent Hanifa Formations possess excellent hydrocarbon attributes such as high total organic content (TOC), and sufficient maturity, combined with a relatively shallow burial depths, allowing for economical unconventional shale gas and shale oil exploitation. Mud gas isotope logging (MGIL) data obtained from recent exploration wells revealed important characterization potential enabling clear distinction between Tuwaiq Mountain, Hanifa and Jubaila Formation gases based on their isotopic signature. A new methane carbon isotopic maturity correlation for the main Tuwaiq Mountain source rock has been calibrated and successfully tested:. VitriniteReflectanceEquivalent(Vre). =.069 × δ13 C1 + 5.13. This finding has permitted accurate maturity assessments providing identification of the best sweet spots predicted for optimal Tuwaiq Mountain production potential. Next stage lateral drilling developments will leverage MGIL technology to assess the effectiveness of future hydraulic fracturing treatments in this formation and ensure maximum in zone completions for best production potential.