Controlling Factors And Evaluation Of Marine Shale Reservoir Capacity In The East Of Chongqing

Shale reservoir is the main factor controls shale gas occurrence state and gas content,which is the main constitution of shale gas resources assessment and sweet spot prediction.However,few studies focused on quantitative evaluation os shale gas reservoir capacity.In this manuscript,geology and geochemistry characters and micro-nanopores structure of the two target intervals,the lower Cambrian Niutitang Formation and lower Silurian Longmaxi Formation in the east of Chongqing,have been detailed studied by data investigation,core observation,experiment test,theoretical analysis and modeling assessment.Accordingly,controlling factors of reservoir capacity have been analyzed,calculated model of shale gas reservoir capacity is proposed and the reservoir capacity has thus been evaluated.Results show that,there are three kinds of micropores developed in the two studied shale intervals with apparently different characters and connectivity.Basically,organic pores developed in the bitumen are better than those in kerogen,interparticle pores are better than intraparticle pores.Besides,the average porosity,pore volume and surface area of Longmaxi shale reservoir are higher than those of Niutitang Formation.Pore volume of Longmaxi Formation are mainly provided by mesopores while Niutitang Formation by mesopores and macropores;surface area of the two formations are provided by micro and mesopores.It can be indicated that the mesopores of Longmaxi Formation are mainly constituted by pores with diameters of 30~50nm while Niutitang Formation by pores with diameters of 10~30nm.As for shale reservoir of one specific interval in the particular area,reservoir capacity of different shale lithofacies are distinctly different: mud/siliceous rich mixed shale and mud rich siliceous shale are the most favorable lithofacies for Longmaxi Formation while mud/siliceous rich mixed shale and siliceous shale are the most favorable lithofacies for Niutitang Formation.It could be concluded that reservoir capacity would be extremely different as a result of differences of preservation condition and thermal evolution,even for the same favorable lithofacies.Reservoir capacity are mainly affected by TOC content,thermal evolution degree,mineral compositions and preservation conditions which have been detailed discussed in this article,and a pore evolution model to reveal the process of pores evolution.Furthermore,a predict model for reservoir capacity has been thus modeled by the factors discussed above,and as a conclusion,reservoir capacity of Longmaxi Foramtion shale in the east of Chongqing is level ?,superior to that of Niutitang Foramtion shale(level ?).Adsorption gas reservoir capacity of both formations are the main reservoir capacity compared with other marine shale formations.