Study On The Quantitative Relation Between Pore Size Distribution And Geological Parameters In Marine And Continental Shales Of China

The pore size distribution(PSD)plays a crucial role in researching pore structure,and it controls the flow and storage capacities of shale gas reservoirs.The main factors affecting the PSD are total organic carbon,mineral compositions,organic matter maturity,permeability,porosity,etc.So far many scholars at home and abroad have studied these geological parameters of shale reservoirs,and there has been considerable literature about experimental research on the pore structure of shale gas reservoirs.However,most of these studies are limited to a certain shale gas reservoir,only analyzing the individuality of this reservoir,and the generality of different shale gas reservoirs hasn't been summarized in a comprehensive way.The PSD of different types of shale is still not well understood.This dissertation first introduces the procedure of deriving multi-peak pore size distribution fitting model which is based on probability density function,then conducts experiment to analyze the geological parameters and pore structure of samples from two typical shale gas reservoirs of China.In addition,the geological parameters and pore structure of another four marine and continental shales of China has been investigated.And two shale gas reservoirs of North America are added to be compared with.Finally,the model is used to quantitatively fit the PSD function,therefore the regular pattern of PSD of marine and continental shale can be researched.The aim of this study is to explore the relationship between the PSD and the geological parameters,consequently the pore structure of shale is able to be predicted by measuring some of the geological parameters,thus helping the exploitation of shale gas.Meanwhile the application of the model is proposed to the prediction of flow capacity in shale reservoirs.It is found that the microscopic pore structure of different shales shows a multimodal distribution.The peaks of fitting curves are concentrated in the radius of 0.5-10 nm,which is consistent with the multi-scale microscopic pore structure characteristics of shale.There is a great difference in the height of the peaks of different shale gas reservoirs.Mesopores occupy the largest proportion of pore volume;besides,micropores and macropores have a much less proportion of pore volume than mesopores do.These three types of pores have a different proportion in different shale gas reservoirs and the micropore volume of the marine shales is larger than that of the continental shales.Shales have complex mineral compositions with a large quantity of clay minerals and brittle minerals.While marine shales have a higher quartz content than continental shales do,continental shales have a higher clay content.Organic matter contributes much to micropores,and clay minerals contribute a little to micropores.Micropore volume shows a good correlation with total organic carbon and thermal maturity.Mesopores mostly develop in clay minerals while macropores mainly develop in brittle minerals.With the increase of clay content,pore volume decreases;on the contrary,a larger percentage of brittle mineral content is correlated with higher pore volume.