A Study On The Drag-Reduction Flow Of Viscoelastic Fracturing Fluid

Drag-reduction agent can decrease flow friction of fracturing fluid significantly,but micro mechanism and macro influencing factors of drag-reduction flow are not well understood and it is lack of a numerical model which can describe drag-reduction flow precisely.Therefore,series of drag-reduction flow experiments in tube have been conducted to study the influence of engineering parameters including shear rate and concentration on drag-reducing rate systematically.Next based on experimental results,a three-dimensional numerical model of drag-reduction flow in tube has been established and validated by DNS(Direct Numerical Simulation)and experimental data.Then sensitivity analyses of elastic parameters are conducted by the model.Firstly,series of drag-reduction flow experiments in tube have been conducted to study the influence of engineering parameters including shear rate and concentration on drag-reducing rate systematically as well as the damage of polymer drag-reduction agent caused by the changing of shear rate.Research shows that drag-reduction rate increases at first and then decreases with the raise of shear rate;high concentration of drag-reduction agent solution has lower drag-reduction rate in low shear rate while higher drag-reduction rate in high shear rate;the “instantaneous damage” in high shear rate can obviously decrease drag-reduction rate and the “accumulating damage” during long time shear rate has little influence on the decrease of drag-reduction rate.Secondly,based on experimental result,according to simultaneous equations of RANS turbulence model and FENE-P viscoelastic constitution,a three-dimensional numerical model of drag-reduction flow in tube has been established and validated by DNS and experimental data.Then sensitivity analyses of elastic parameters are conducted by the model.Research shows that drag-reduction rate increases with the raise of both relaxation time and maximum extensibility of molecule;there is an upper limit of the drag-reduction rate increasing with maximum extensibility of molecule;the raise of relaxation time can enhance that upper limit.At last,according to the fracturing fluid test of Well An-XX in Ordos Basin,some suggestions of parameters optimizing are proposed to increase drag-reducing rate: increasing displacement and selecting a drag-reducing agent with higher relaxation time can both improve drag-reducing rate effectively.