Experimental study on the stress sensitivity of coal and its impact on the filtration of the fracturing fluid

The filtration coefficient of fracturing fluid is an important parameter in fracturing design.If the per-meability and porosity values obtained from well testing and logging are directly substituted into the equation of calculating filtration coefficient,the results calculated may be entirely different from the practical case,because the petrophysical parameters such as permeability and porosity,etc.are very sensitive to the stress in coal bed.Coal bed reservoir,fractured reservoir and tight sand reservoir are typical sensitive reservoirs.So it is necessary to study the stress sensitivity in coal bed.In the article the relationship between the stress and permeability in the coal res-ervoir was set up by simulating the coal reservoir pressure suffered by the overlying formation.And the method of calculating overall filtration coefficient during fracturing in coal bed is also generally discussed.The results show that both the overall filtration coefficient and permeability accord with the exponential decline law.Besides,on the basis of fitting of the dynamic permeability,the overall filtration coefficient under the consideration of stress sen-sitivity is higher than that which doesn't consider the stress sensitivity,which is more practical and can describe the actual situation.