Biogenic Gas Potential in Abu Dhabi

Abstract

Abstract Recently there has been a growing interest in gas exploration, much of this focus has been directed toward thermogenic gas derived from cracking kerogen in the highly mature kitchens. However, a significant proportion of the global gas reserve is not thermogenic but of bacterial origin (Katz, 1995). Biogenic gas is an important exploration target because it occurs in geologically predictable circumstances, in areally widespread area, and in large quantities at shallow depths as free gas (Schneider et al, 2016). The recent exploration wells drilled in the northeast onshore Abu Dhabi showed elevated total gas readings during the drilling of the Gachsaran formation. Consequently, mud-weight was increased to control the gas flow. In addition, the recorded wireline logs indicate the presence of relatively high hydrocarbon saturations in several high porous zones of Gachsaran and Asmari formations. To assess the productivity and commerciality of the Biogenic gas potential in Abu Dhabi, several exploration wells are planned to be drilled before the end of 2019. The positive results of these wells will open the door for a new era of sweet gas exploration activities in Abu Dhabi and its surrounding areas. The primary gas reservoirs are thin carbonate and clastics layers in the Gachsaran Formation at a depth that ranges between 1600-5200 feet below sea level. Organic carbon isotopes, Rock Eval analysis, TOC log data and gas shows analysis indicated that the methane gas found in the Gachsaran Formation is of a biogenic origin and sourced mainly from the organic-rich argillaceous limestone of the Middle Gachsaran. Gachsaran formation is comprised of alternating thin layers of anhydrite, limestone, marl and shale sediments in addition to the presence of salt layers in the lower part. This mixed lithology resulted in the reservoirs property deterioration in particular by shale and anhydrite nodules cementation. The biogenic basin areal extent, significant thickness of the Gachsaran in this basin and the organic richness distribution, conclude possible generation of a huge volume of biogenic gas in northeast onshore Abu Dhabi. However, additional work is required to estimate the volume of gas that is accumulated and that can be produced from the Gachsaran and Asmari formations.