Reservoir forming characteristics and favorable area evaluation of deep coalbed methane in southeastern Chongqing
The coalbed methane Y2 well of the Permian Longtan Formation in Nanchuan Block of southeastern Chongqing has a daily gas production of 1.3 X 104 m3,demonstrating good exploration potential for deep coalbed methane.However,the reservoir characteristics of deep coalbed methane are not yet clear.Taking Nanchuan-Xinchang-Dingshan block as the research objects,the reservoir characteristics and sweet spot areas of deep coalbed methane was researched based on the data analysis of coalbed methane well test,testing and production test.The results showed that the deep coalbed methane in Longtan Formation in the study area is controlled by sedimentary differences.Nanchuan Block develops tidal flat carbonate platform deposits,with 2～4 coal seams and a total thickness of 2～4 m.Dingshan Block is tidal flat deposits,with 6～8 coal seams and a total thickness of 5～10 m.Deep coal reservoirs have high evolution,with Ro ranging from 1.7％to 2.4％.Pores and fractures are developed,and adsorbed gas is stored in micropores.Free gas is mainly stored in macropores and cleavage fractures.The reservoir has the conditions for the co occurrence of adsorbed gas and free gas.The top and bottom plates are mainly composed of limestone and mudstone,with strong sealing ability.The mineralization degree of the formation water is greater than 10 g/L,and the water type is CaCl2,with good preservation conditions.Deep coalbed methane has the characteristics of medium to high evolution,high gas content,high saturation,and abundant free gas in favorable preservation areas.We have established 16 evaluation indicators for deep coalbed methane geological engineering double sweet spots,divided them into 3 types of sweet spot areas,and selected a favorable area of 2 599 km2 with a depth of 1 500 m.The estimated resource amount is 5 457 × 108 m3,which has guiding significance for the exploration of deep coalbed methane in the south.
deep reservoircoalbed methanereservoir forming characteristicgeo-engineering sweet spot
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