Effects of Paleozoic carbonate rock on shale gas accumulation and exploitation in southern China

The dark shale of Paleozoic is widely present in southern China, but little progress has been made in exploration of shale gas. One reason for this is the co-existence of carbonate that complicates the geological condition. Based on experiences from abroad and southern China on this issue in recent years, this paper discusses five problems,(1) How the surface or nearsurface karst geology poses impact on exploitation of shale gas; (2) the influences of roof and floor of a shale layer and carbonate within the layer on the accumulation and mining; (3) the effect of carbonate mineral content in the shale on fracturing during production; (4) the influence of natural cracks in shale formation with calcite filling on gas accumulation; and (5) co-accumulation of conventional and carbonate reservoirs and unconventional shale reservoirs. Finally, this work suggests to make an comprehensive consideration on the exploration of shale gas in southern China, involving accumulation of carbonate itself and its effect on accumulation, exploitation, and drilling of shale gas. Thus a new line of thought on the hydrocarbon system can be established, which will guide reasonable deployment of drill holes and further exploration of shale gas.