Methane Gas seeps in the southern Bangladesh: Origin and Distribution

English Abstract:

Recent studies shows remarkable amounts of methane, are naturally released into the atmosphere from the Earth’s crust through faults and fractured rocks. The main source is natural gas, both microbial and thermogenic, produced in hydrocarbon-prone sedimentary basins and injected into the atmosphere through macro-seeps and micro-seepage, an invisible but pervasive flux from the soil. Eastern part of Bangladesh, a proven gas rich province has a few gas fields with surface seepages. Among them, two gas fields Titas and Shahbazpur show significant gas seepages for more than a decade. While Titas gas field (5.5 Tcf) seepage is anthropogenic i.e. due to drilling problem, the gas seepage in Shahbazpur gas field (0.5 Tcf) is natural. Historical data based on the community interaction suggests Shahbazpur gas field has been seeping gas through the surface for more than 30 years. There are 6 major gas zones in the shahbazpur gas field. But only 3 gas zones are now producing gas. The average thickness of the gas zones is about 50 m and the depth of the gas zones ranges from 3248 m to 3355 m. There has been no work or research done on the origin and extent of the seepage in Shahbazpur gas field to date. The main objective of this research is to systematically documenting the nature, distribution and degree of seepage in Shahbazpur area and to find out possible outcome. Microbial degradation produces hydrocarbon gas with C1/ (C2 +C3) ratios*greater than 1000, i.e., almost exclusively methane. This methane products usually have carbon isotope ratios lighter than -60%. The analysis of gas sample can be done by compositional gas analysis and isotopic analysis. We are expecting the source of the gas is shallow microbial decomposition of organic matter that is biogenic because its low flow rate to the surface and dry nature. The seepage gas can be found by local deep water well. Deep deposits of hydrocarbons, including varied reservoirs of petroleum and natural gas, represent the most economically important component of the deep carbon cycle.