The Experimental Research Of The Effect Of Slick Water On The Wetting And Swelling Of Shale Formation

As the gas reservoir of the unconventional natural gas,the shale has the advantages of the coexistence of adsorbed gas and free gas,the severe heterogeneity,low porosity and low permeability.In order to exploit the shale gas efficiently,the massive volume fracturing was widely used to increase the seepage area.However,the study found that the flowback rate of the fracturing fluid in the Fuling site is less than 10 %,indicating that a lot of Slick water was detained in the reservoir.As one of the crucial factors in the fracturing,the fracturing fluid was affected by its formula.The additives in the fluid formula have the core influence on the result of fracturing and gas deliverability because the additives affect the reservoir properties of wettability and dilatability.So the influence of slick water detained in the reservoir was particularly important.Through the study of factors affecting the smooth water retention in the reservoir,the Fuling Jiao Shi Longmaxi black siliceous and carbonaceous shale outcrop samples,in different systems,different concentration of shale wetting liquid,swelling experiment,and get the influence of permeability change.The results of the experiments can be listed as follow.(1)The rock specimens the scanning electron microscope and the x-ray diffraction.The mineral components and the pore structure of the rock were analyzed.The results of this study are consistent with the geological characteristics of the core rocks in the fracturing zone of Fuling gas field,which lays the foundation for the study of wettability and expansibility,and provides a scientific basis for field application.(2)The measure of the hydrophilic-hydrophobic property of the LLE shale particle indicated that the shale was serve heterogeneous soaked.The wettability of the shale surface soaked by the distilled water is better than the quick water because the matrix of the shale is hydrophilic.The extension of the soak time made the shale more hydrophilic which was beneficial for the the quick water to enter the formation,extend the micro fracture and increase the permeability.The drag reducer had the most obvious effect on the wettability.Before and after 0.05%~0.1% concentration,the wetting angle decreased first and then increased.The matrix permeability of the soaked shale increased about 1 time.(3)The ratio of hydrate swelling and swell capacity of the shale increased with the rising temperature and decreased with the rising pressure.And the influence of the temperature was strong than the pressure.With the increasing time of the quick water detained in the shale,thefunction of the hydration and swelling was stronger,the water saturation was higher and the extension of the pore and crack was more obvious.The experiment found that shale swelling rate is not as high as possible,the actual effect of fracturing additives increase the fracturing fluid intake,increase the permeability of shale swelling caused by broken,and at the same time,can also cause clay mineral swelling decreased pore circulation,blocked pores.Among all additives,the drag reducer had the most important effect on the expansion rate.The change of the concentration of anti swelling agent has the greatest influence on the expansion rate of shale,and the expansion rate is the best under the condition of 0.2% concentration,and the others are drag reducing agent,synergist and defoaming agent.In this paper,the formula of fracturing fluid additive The research reveals the influence mechanism that.the quick water affects the permeability of the shale gas.In addition,the research has the theory and practice significance on the optimization design of the fracturing fluid in Fuling.