Geo Trivia

(6) What happen to the gas reservoirs in Khorat Plateau during “TSR” ?
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"TSR" is the process of selective consuming hydrocarbon (Zhu Guang You et al., 2007). During "TSR" process, the chemical activity of methane (C1) is weaker than that of C2 and C3 … etc… Meaning the heaviest hydrocarbons must be altered first and C1 is the last. This process decreases the amount of heavy hydrocarbons. In addition, the high temperature condition also increases the thermal maturation and increases the thermal cracking of heavy hydrocarbons. Hence,at the end, the gas pool will become very dry.
By the fact that one field here is producing methane and condensate. It can simply be explained that the “TSR” had stopped before the gas was completely turned to methane (C1) either by the use up of sulfates or the thermal maturation was disrupted.
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This article is a series of “Gas Fields onshore Thailand”. It is my personal interpretation. The onshore gas fields mentioned here are located in the NE of Thailand where known as Khorat Plateau.
(1) Gas Fields onshore Thailand
(2) Gas Characteristics in NE Thailand
(3) Origin of H2S
(4) Why I believe “TSR” is the major mechanism to generate the H2S
(5) How “TSR” works?
(6) What happen during “TSR”?

Gas fields in Khorat, NE Thailand
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5. How “TSR” works ? …. .. “TSR” ทำงานอย่างไร?
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Three factors are vitally and inevitably needed to ignite “TSR” to begin. They are: (1) sulfates, (2) hydrocarbons and (3) high temperature. The gas traps must be subsided to a great depth where the temperature is more than 100 degC. The gas traps in NE Thailand are at depth 3 km at the 120 degC. This is perfect for the “TSR”. However, at high temperature, the thermal cracking also begins. Therefore, while H2S is forming by TSR process, the thermal cracking is also working and cracking down the hydrocarbon molecules from wet gas to dry gas.