Applying Adsotption Isotherms To Research Characteristics Of Pore Structure Of Shale

In recent years,shale gas revolution has already spread all over the world.And eight shale gas production areas has formed in North American such as Eagle Ford,Barnett,Marcellus and Green River.The proved recoverable reserves is about 24 trillion cubic meters.From 2006 to 2012,the total natural gas production in American has increased from 5232 trillion to 6814 trillion cubic meters.Shale gas production in the proportion of the total gas production is from 2 percent rise to 37 percent.China,India,Europe,New Zealand,Australia and other countries or regions launched pilot experiments of shale gas exploration and Selection evaluation in session.Sinopec and Petrochina has made a breakthrough in shale gas exploration in SiChuan basin,upper Paleozoic continental shale and marine shale.And Strengthened in shale gas evaluation method and the accumulation mechanism research.The core issue of unconventional shale gas exploration is searching for shale reservoir.Understanding of shale micron and nanoscale pore structure characteristic is an emphasis and difficulty in researching shale reservoir.This is of great significance on selecting shale gas well horizontal,evaluating potential of development and calculating of gas seepage ability.Analyzing the pore structure features is an important part of shale reservoir evaluation.Shale lithology is tight.Shale reservoir has a great deal of micro-pore.Analytical methods on regular pore structure has limitations on shale.In the study of shale reservoir pore characteristics,using the combined of mercury intrusion method and adsorption method more.For shale adsorption,different core samples vary in pore characteristic,has led to the difference of its adsorption performance.This will reflect on the type of isothermal adsorption curves.The technology of shale reservoir evaluation is a key skill of shale gas exploration and exploitation.This article is based on the traditional classification of isothermal adsorption curves as BDDT classification,De Bore classification,IUPAC classification and Gibbs classification.Then absorbing the achievements of predecessors' experience,combining with Thommes adsorption theory and Peter adsorption experiment to analyze the characteristics of shale pore structure in reflection of isothermal adsorption curves.Establishing a new classification for shale isothermal adsorption curves to evaluate the characteristics of shale pore structure.Including: pore shape,pore size,and pore segregation.This work provides a methodology system in application of analyzing isothermal adsorption curves to discuss the characteristics of shale pore structure.From the low temperature of nitrogen isothermal adsorption experiment,obtaining the isothermal adsorption curves of liquid nitrogen adsorption and adsorption quantity in the shale as well as the corresponding relative pressure data.Priority from the method of classification of isothermal adsorption curves,qualitative analyzing the pore structure characteristics of shale samples.According to the new classification for shale isothermal adsorption curves,analyzing the pore shape,pore size and pore segregation three factors for shale samples.Combining with scanning electron microscopy(SEM)and aperture frequency histogram to auxiliary analysis and verification.Combining BET linear equation with Halsey equation to analyze capillary condensation phenomenon according to each shale samples' isothermal adsorption curves.Then finding its initial relative pressure points and adsorption layer thickness under a certain relative pressure for each shale samples.Through the modified BJH algorithm to recalculate the distribution of pore size from isothermal adsorption experiment.To achieve the quantitative analysis of pore size for shale samples.At last combined with two methods to reach the effect of evaluating the characteristics of shale pore structure from the qualitative to the quantitative through isothermal adsorption curves.And compared research methods of pore structure between this paper and predecessors.