Study On Evaluation Method Of Shale Gas Content

With the increasing dependence on energy imports in China,more and more attention has been paid to shale gas exploration and development.Gas content is an important parameter index of shale gas reservoir evaluation.Its value directly affects whether the shale gas block has industrial development value,and plays an extremely important role in promoting the study of shale gas reservoir formation mechanism,and has important guiding significance for improving the accuracy of shale gas resource evaluation.In this paper,the mineral composition,organic matter carbon content(TOC),vitrinite reflectance Ro,porosity,permeability and other basic parameters of shale samples were studied experimentally,and the basic physical properties of shale samples were evaluated.On this basis,the experiments of adsorption and desorption of shale were carried out,the influencing factors of shale gas content were studied,the influencing factors model was established,and the influencing factors of adsorption gas and free gas content were analyzed.Finally,according to the analytical method to measure shale gas content,based on the shale pressure reduction mining experiment,shale samples are selected to carry out natural exploitation simulation experiments at different pressure drop rates.Loss gas and desorption gas are measured by the experiment,and residual gas is calculated by ORIGIN numerical software.The final sum of the three parts of gas content is shale gas content.The law of gas production under different pressure drop rates and the proportion of shale gas loss were compared.The influence of lifting speed on the calculation accuracy of shale gas content and how to quantify the lost gas were discussed.The experimental results show that the shale samples are mainly composed of clastic minerals,clay minerals and brittle minerals,mainly clastic minerals;the TOC content of organic matter is 2.4%-7.6%,and the average vitrinite reflectance Ro is more than 2.5%.The shale samples are in the stage of over-mature evolution and have great potential for development;the porosity range is 2.685%-8.922%,the permeability range is 0.002-0.01?m~2,and the pore-permeability structure is very poor.By establishing the factor model of influencing gas content and calculating the multiple correlation coefficient between each factor and shale gas content,it is known that organic carbon content is the most important parameter affecting shale gas content,and clay mineral content is the minimum parameter affecting shale gas content.The shale samples were subjected to the depressurization desorption experiment.The loss gas volume and the desorption gas volume were measured in turn.The ORIGIN numerical software was used to fit the residual gas volume.The results show that the sample analysis method can be divided into three stages:the initial gas production.The rate is the highest,then the gas production rate shows a relatively stable step,and finally the gas production rate gradually decreases.With the increase of the depressurization rate,the gas production rate corresponding to the step is higher,the gas production end time is shorter,and the loss gas volume ratio is reduced.small.In addition,the average loss of gas in the test sample is 40%-50%.Therefore,in the shale gas content measurement experiment,the core should be lifted quickly to reduce the loss of gas.If the core rate is low,the loss of gas should be restored substantially to ensure the accuracy of gas content measurement.