| Desorption characteristics reflect shale gas enrichment and its preservation conditions indirectly. Marine shale
gas desorption types and their genesis in southern China have been divided and evaluated by thermal variation desorption
test and gas constitution test. There are four marine shale gas desorption types. The atmospheric temperature desorption
shale gas desorbed greatly under atmospheric temperature, the desorbed gas was mainly methane. Its main causes are
ascribed to a good gas generation material base and preservation conditions, as well as well-developed fracture system. The
reservoir temperature desorption shale gas desorbed greatly under reservoir temperature, the desorbed gas was also mainly
methane. Its cause is ascribed to the absence of pressure sealing conditions formed mainly by weak caprock sealing and
lateral dissipation. The high temperature desorption shale gas desorbed greatly under a high temperature above 90 ℃, the
desorbed gas had relatively high O2 and N2 contents. Its causes are ascribed to shallow burial condition and destroyed
preservation condition. High temperature-low content desorption shale gas desorbed a little gas under a high temperature
above 90 ℃, the desorbed gas had little hydrocarbon. Its causes are ascribed to long time deep burial history and destroyed
preservation condition. The atmospheric temperature desorption shale gas had better exploration and development condition,
however, the reservoir temperature desorption shale gas maybe lack of economical development conditions at present. The
other two types of shale gas are not worth further exploration. |
