Reservoir damage caused by guar gum fracturing fluid and slick water seriously affects the subsequent oil and gas production. However, the invasion characteristics and retention mechanisms of fracturing fluids in the ...Reservoir damage caused by guar gum fracturing fluid and slick water seriously affects the subsequent oil and gas production. However, the invasion characteristics and retention mechanisms of fracturing fluids in the fracture-matrix zone are still unclear. In this work, a microscopic model reflecting the characteristics of the fracture-matrix zone was designed. Based on the microfluidic experimental method, the process of fracturing fluid invasion, flowback and retention in the fracture-matrix zone was investigated visually and characterized quantitatively. The factors and mechanisms affecting fracturing fluid retention in the fracture-matrix zone were analyzed and clarified. The results indicated that in the invasion process, the frontal swept range of slick water was larger than that of the guar gum fracturing fluid, and the oil displacement efficiency and damage rate were lower than those of the guar gum fracturing fluid under the same invasion pressure. With the increase in invasion pressure, the damage rate of slick water increased from 61.09% to 82.77%, and that of the guar gum fracturing fluid decreased from 93.45% to83.36%. Before subsequent oil production, the invaded fracturing fluid was mainly concentrated in the medium-high permeability area of the fracture-matrix zone. The main resistance of slick water was capillary force, while that of the guar fracturing fluid was mainly viscous resistance. The fracturing fluid retention was most serious in the low permeability region and the region near the end of the fracture.The experimental and numerical simulation results showed that increasing the production pressure difference could improve the velocity field distribution of the fracture-matrix zone, increase the flowback swept range and finally reduce the retention rate of the fracture fluid. The retention mechanisms of slick water in the fracture-matrix zone include emulsion retention and flow field retention, while those of the guar gum fracturing fluid include viscous retention and flow field retention. Emulsion retention is caused by capillary force and flow interception effect. Viscous retention is caused by the viscous resistance of polymer, while flow-field retention is caused by uneven distribution of flowback velocity.展开更多
The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir r...The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir remain unclear. The flowback efficiencies of different types of surfactant micellar solutions were evaluated by core experiments, a multi-level pore-throat system micromodel characterizing pore-throat structures of low permeability reservoir was made, and flooding and flowback experiments of brine and surfactant micellar solutions of different salinities were conducted with the micromodel to show the oil flowback process in micron pores under the effect of surfactant micellar solution visually and reveal the mechanisms of enhancing displacement and flowback efficiency of surfactant micellar solution. During the displacement and flowback of brine and low salinity surfactant micellar solution, many small droplets were produced, when the small droplets passed through pore-throats, huge percolation resistance was created due to Jamin’s effect, leading to the rise of displacement and flowback pressure differences and the drop of flowback efficiency. The surfactant micellar solutions with critical salinity and optimal salinity that were miscible with crude oil to form Winsor Ⅲ micro-emulsion didnot produce mass small droplets, so they could effectively reduce percolation resistance and enhance oil displacement and flowback efficiency.展开更多
Immiscible displacements in porous media are fundamentally significant for many natural processes and industrial applications.Although extensive work has been done in this field,some limitations still exist due to the...Immiscible displacements in porous media are fundamentally significant for many natural processes and industrial applications.Although extensive work has been done in this field,some limitations still exist due to the difficulty to cover the large number of influencing factors.In this paper,we present a systematic study involving the coupled influence of capillary forces,viscous forces,wetting properties and pore geometries.By microfluidic experiments with high resolutions,both residual fluid distributions and dynamical invasion processes were clearly captured and quantitatively characterized.A void-filling behavior was identified for drainage as the capillary number Ca increased.An anomalous void-leaving behavior was found for the case of imbibition with an unfavorable viscosity ratio M,representing many ribbon-like regions invaded at intermediate Ca turned to be not accessible at high Ca.A pore geometry with a large typical pore-throat ratio seemed to enhance the void-leaving behavior.During the dynamical invasion processes,an intermittency behavior was captured in the form of a fluctuation of the increasing rate of the invading saturation with time.The intermittency dynamics were most evident for drainage with an unfavorable M.A pore geometry with high porosity acted to suppress the intermittency behaviors.Our experimental results sketched out a full view of immiscible displacements in porous media under different conditions,and provided a complete dataset which could be used to test the rapid developing pore-scale models.展开更多
基金supported by the National Natural Science Foundation of China (No. 51874330, 51974341)the Fundamental Research Funds for the Central Universities (No. 20CX06070A)the Opening Fund of Shandong Key Laboratory of Oilfield Chemistry and the Fundamental Research Funds for the Central Universities(No. 19CX05006A)。
文摘Reservoir damage caused by guar gum fracturing fluid and slick water seriously affects the subsequent oil and gas production. However, the invasion characteristics and retention mechanisms of fracturing fluids in the fracture-matrix zone are still unclear. In this work, a microscopic model reflecting the characteristics of the fracture-matrix zone was designed. Based on the microfluidic experimental method, the process of fracturing fluid invasion, flowback and retention in the fracture-matrix zone was investigated visually and characterized quantitatively. The factors and mechanisms affecting fracturing fluid retention in the fracture-matrix zone were analyzed and clarified. The results indicated that in the invasion process, the frontal swept range of slick water was larger than that of the guar gum fracturing fluid, and the oil displacement efficiency and damage rate were lower than those of the guar gum fracturing fluid under the same invasion pressure. With the increase in invasion pressure, the damage rate of slick water increased from 61.09% to 82.77%, and that of the guar gum fracturing fluid decreased from 93.45% to83.36%. Before subsequent oil production, the invaded fracturing fluid was mainly concentrated in the medium-high permeability area of the fracture-matrix zone. The main resistance of slick water was capillary force, while that of the guar fracturing fluid was mainly viscous resistance. The fracturing fluid retention was most serious in the low permeability region and the region near the end of the fracture.The experimental and numerical simulation results showed that increasing the production pressure difference could improve the velocity field distribution of the fracture-matrix zone, increase the flowback swept range and finally reduce the retention rate of the fracture fluid. The retention mechanisms of slick water in the fracture-matrix zone include emulsion retention and flow field retention, while those of the guar gum fracturing fluid include viscous retention and flow field retention. Emulsion retention is caused by capillary force and flow interception effect. Viscous retention is caused by the viscous resistance of polymer, while flow-field retention is caused by uneven distribution of flowback velocity.
基金Supported by the China National Science and Technology Major Project (2017ZX05009-005-003)Research Fund of China University of Petroleum (Beijing)(2462019QNXZ04)。
文摘The existing researches on surfactant micellar solutions mainly focus on the formulation optimization and core flooding test, and the types and mechanisms of cleanup additives suitable for low permeability reservoir remain unclear. The flowback efficiencies of different types of surfactant micellar solutions were evaluated by core experiments, a multi-level pore-throat system micromodel characterizing pore-throat structures of low permeability reservoir was made, and flooding and flowback experiments of brine and surfactant micellar solutions of different salinities were conducted with the micromodel to show the oil flowback process in micron pores under the effect of surfactant micellar solution visually and reveal the mechanisms of enhancing displacement and flowback efficiency of surfactant micellar solution. During the displacement and flowback of brine and low salinity surfactant micellar solution, many small droplets were produced, when the small droplets passed through pore-throats, huge percolation resistance was created due to Jamin’s effect, leading to the rise of displacement and flowback pressure differences and the drop of flowback efficiency. The surfactant micellar solutions with critical salinity and optimal salinity that were miscible with crude oil to form Winsor Ⅲ micro-emulsion didnot produce mass small droplets, so they could effectively reduce percolation resistance and enhance oil displacement and flowback efficiency.
基金supported by the National Natural Science Foundation of China(51876100)the Science Fund for Creative Research Group(No.51621062).
文摘Immiscible displacements in porous media are fundamentally significant for many natural processes and industrial applications.Although extensive work has been done in this field,some limitations still exist due to the difficulty to cover the large number of influencing factors.In this paper,we present a systematic study involving the coupled influence of capillary forces,viscous forces,wetting properties and pore geometries.By microfluidic experiments with high resolutions,both residual fluid distributions and dynamical invasion processes were clearly captured and quantitatively characterized.A void-filling behavior was identified for drainage as the capillary number Ca increased.An anomalous void-leaving behavior was found for the case of imbibition with an unfavorable viscosity ratio M,representing many ribbon-like regions invaded at intermediate Ca turned to be not accessible at high Ca.A pore geometry with a large typical pore-throat ratio seemed to enhance the void-leaving behavior.During the dynamical invasion processes,an intermittency behavior was captured in the form of a fluctuation of the increasing rate of the invading saturation with time.The intermittency dynamics were most evident for drainage with an unfavorable M.A pore geometry with high porosity acted to suppress the intermittency behaviors.Our experimental results sketched out a full view of immiscible displacements in porous media under different conditions,and provided a complete dataset which could be used to test the rapid developing pore-scale models.
