Screening And Performance Evaluation Of Supercritical Carbon Dioxide Thickener

Due to unique properties,supercritical CO₂ has attracted extensive attention in the exploitation of unconventional oil and gas reservoirs.However,the using of it is limited in practical application because of its low viscosity and poor performance in carrying proppants.Currently,the viscosity of supercritical CO₂ is generally increased by adding the thickener.Therefore,in this thesis,firstly screens out the thickener SC-T-18 with excellent solubility in CO₂ though experiments.Then,taking the molecular model of the optimized thickener as the research object,by using molecular dynamics simulations.The microstructure is observed,and the viscosity of thickener is calculated.The kinetic structure of thickener was characterized by diffusion coefficient and interaction of polymer groups,so as to have some insight to the microscopic information of the thickener.Finally,through experiments evaluating the rheological property,suspended sand property,friction property and damage to core caused by CO₂ thickening fracturing fluid.The result of the research shows that:?1?SC-T-18 thickener can dissolve in liquid and supercritical CO₂ to form single,homogeneous and stable emulsion micelle.?2?The polymer groups have the different binding capacity to the supercritical CO₂ molecules,which is mainly caused by the thickener molecular space network structure inhibits the movement of CO₂ molecules.Moreover Van der Waals interaction is the primary constraint interaction.?3?The optimal addition amount of SC-T-18 thickener is 2wt%,and the increase amplitude of viscosity is nearly 50 times.The viscosity of supercritical CO₂ fracturing fluid system decreases sharply with the increase of shear rate,indicating that it is a non-newton fluid.Besides,the temperature has a significant effect on system viscosity.The main reason is that the increase of temperature intensifies the destruction of the intermolecular network structure of the thickener,so the viscosity is significantly reduced.When the pressure increases,the viscosity increases.The reasons are as follows:for one thing,the solubility of the thickener in CO₂ increases when the pressure increases.For the other reason,the increase of pressure makes the intermolecular space decrease.?4?Adding a certain amount of thickener is beneficial to reduce the propping agent settling rate and improve the sand carrying performance.It also have the certain drag reduction effect.The average damage rate of CO₂ fracturing fluid system on shale core is 2.1%.CO₂ can be dissolved in water and CO₂ is miscible with crude oil,with excellent formation compatibility.