In this paper,marine shale cores taken from Zhaotong,Changning and Weiyuan Blocks in South China were used as samples to investigate the interaction between fracturing fluids and shale and the retention mechanisms.Fir...In this paper,marine shale cores taken from Zhaotong,Changning and Weiyuan Blocks in South China were used as samples to investigate the interaction between fracturing fluids and shale and the retention mechanisms.Firstly,adsorption,swelling,dissolution pore,dissolution fluid mineralization degree and ionic composition were experimentally studied to reveal the occurrence of water in shale and the reason for a high mineralization degree.Then,the mechanisms of water retention and mineralization degree increase were simulated and calculated.The scanning electron microscopy(SEM)analysis shows that there are a large number of micro fractures originated from clay minerals in the shale.Mineral dissolution rates of shale immersed in ultrasonic is around 0.5-0.7%.The ionic composition is in accordance with that of formation water.The clay minerals in core samples are mainly composed of chlorites and illites with a small amount of illites/smectites,but no montmorillonites(SS),and its content is between 18%and 20%.It is verified by XRD and infrared spectroscopy that the fracturing fluid doesn't flow into the space between clay mineral layers,so it can't lead to shale swelling.Thus,the retention of fracturing fluids is mainly caused by the adsorption at the surface of the newly fractured micro fractures in shale in a mode of successive permeation,and its adsorptive saturation rates is proportional to the pore diameters.It is concluded that the step-by-step extraction of fracturing fluids to shale and the repulsion of nano-cracks to ion are the main reasons for the abrupt increase of mineralization degree in the late stage of flowing back.In addition,the liquid carrying effect of methane during the formation of a gas reservoir is also a possible reason.Based on the experimental and field data,fracturing fluid flowback rates and gas production rates of 9 wells were analyzed.It is indicated that the same block follows an overall trend,namely,the lower the flowback rates,the more developed the micro fractures,the better the volume simulation effect and the higher the gas production rates.展开更多
It is widely stated that most organic contaminants could be completely mineralized by Advanced Oxidation Processes(AOPs). This statement means that the concentration of the organic contaminant at equilibrium(limiting ...It is widely stated that most organic contaminants could be completely mineralized by Advanced Oxidation Processes(AOPs). This statement means that the concentration of the organic contaminant at equilibrium(limiting concentration,LC)is low enough to be neglected.However,for environmental safety,especially drinking water safety,this statement needs to be verified from chemical engineering thermodynamic analysis.In this paper,trichloromethane(CHCl3)and dichloromethane(CH2Cl2) are selected as the model systems,and the equilibrium concentration(theoretical limiting concentration,TLC)for the mineralization of chlorinated methanes in aqueous solutions at the different initial concentrations of chlorinated methanes,pH values and·OH concentrations by AOPs are investigated by thermodynamic analysis.The results in this paper show that the TLC for the mineralization of CHCl3 and CH2Cl2 with·OH increases with increasing initial concentrations of CHCl3 and CH2Cl2,decreases with increasing concentration of·OH,and the TLC for the mineralization of CHCl3 decreases with increasing pH values except that the pH value changes from 3.0 to 3.5.For the mineralization of CH2Cl2 with·OH,at the concentrations of·OH obtained from the literature,there is no obvious change of the TLC with pH values,while as the concentrations of·OH increase by 10 and 100 times,the TLC decreases with the increasing pH values from 2.0 to 3.0 and from 3.5 to 4.5,and increases with the increasing pH values from 3.0 to 3.5 and from 4.5 to 5.0.The investigations in this paper imply that high concentration of·OH,a bit higher pH values(4.0–5.0)in acid environment and low initial concentrations of the organic contaminants are beneficial for the complete mineralization of chlorinated methanes by AOPs.展开更多
基金Project supported by National Key Basic Research Program of China(937 program)“Basic research of high-efficiency marine shale gas development in South China”(No.2013CB228000).
文摘In this paper,marine shale cores taken from Zhaotong,Changning and Weiyuan Blocks in South China were used as samples to investigate the interaction between fracturing fluids and shale and the retention mechanisms.Firstly,adsorption,swelling,dissolution pore,dissolution fluid mineralization degree and ionic composition were experimentally studied to reveal the occurrence of water in shale and the reason for a high mineralization degree.Then,the mechanisms of water retention and mineralization degree increase were simulated and calculated.The scanning electron microscopy(SEM)analysis shows that there are a large number of micro fractures originated from clay minerals in the shale.Mineral dissolution rates of shale immersed in ultrasonic is around 0.5-0.7%.The ionic composition is in accordance with that of formation water.The clay minerals in core samples are mainly composed of chlorites and illites with a small amount of illites/smectites,but no montmorillonites(SS),and its content is between 18%and 20%.It is verified by XRD and infrared spectroscopy that the fracturing fluid doesn't flow into the space between clay mineral layers,so it can't lead to shale swelling.Thus,the retention of fracturing fluids is mainly caused by the adsorption at the surface of the newly fractured micro fractures in shale in a mode of successive permeation,and its adsorptive saturation rates is proportional to the pore diameters.It is concluded that the step-by-step extraction of fracturing fluids to shale and the repulsion of nano-cracks to ion are the main reasons for the abrupt increase of mineralization degree in the late stage of flowing back.In addition,the liquid carrying effect of methane during the formation of a gas reservoir is also a possible reason.Based on the experimental and field data,fracturing fluid flowback rates and gas production rates of 9 wells were analyzed.It is indicated that the same block follows an overall trend,namely,the lower the flowback rates,the more developed the micro fractures,the better the volume simulation effect and the higher the gas production rates.
基金supported by the Chinese National Key Technology Research and Development Program(2006AA03Z455)NSFC-RGC(20731160614)+2 种基金Program for Changjiang Scholars and Innovative Research Team in Univer-sity(IRT0732)National Basic Research Program of China(2009CB226103)the National Natural Science Foundation of China(20976080)
文摘It is widely stated that most organic contaminants could be completely mineralized by Advanced Oxidation Processes(AOPs). This statement means that the concentration of the organic contaminant at equilibrium(limiting concentration,LC)is low enough to be neglected.However,for environmental safety,especially drinking water safety,this statement needs to be verified from chemical engineering thermodynamic analysis.In this paper,trichloromethane(CHCl3)and dichloromethane(CH2Cl2) are selected as the model systems,and the equilibrium concentration(theoretical limiting concentration,TLC)for the mineralization of chlorinated methanes in aqueous solutions at the different initial concentrations of chlorinated methanes,pH values and·OH concentrations by AOPs are investigated by thermodynamic analysis.The results in this paper show that the TLC for the mineralization of CHCl3 and CH2Cl2 with·OH increases with increasing initial concentrations of CHCl3 and CH2Cl2,decreases with increasing concentration of·OH,and the TLC for the mineralization of CHCl3 decreases with increasing pH values except that the pH value changes from 3.0 to 3.5.For the mineralization of CH2Cl2 with·OH,at the concentrations of·OH obtained from the literature,there is no obvious change of the TLC with pH values,while as the concentrations of·OH increase by 10 and 100 times,the TLC decreases with the increasing pH values from 2.0 to 3.0 and from 3.5 to 4.5,and increases with the increasing pH values from 3.0 to 3.5 and from 4.5 to 5.0.The investigations in this paper imply that high concentration of·OH,a bit higher pH values(4.0–5.0)in acid environment and low initial concentrations of the organic contaminants are beneficial for the complete mineralization of chlorinated methanes by AOPs.
