Study On Formation Mechanism Of Blockage And Preventions Of Plugging In Polymer Injection Well

Polymer flooding is widely used in tertiary oil recovery.It has significantly improved oil recovery in the application.However,there are many problems in the subsequent process of polymer flooding,such as the increase of polymer injection pressure,the decrease of polymer injection velocity and so on.It seriously affects the effect of polymer flooding.Strong oxidizer is a traditional plugging agent,but Its security is low and the effect is bad.Therefore,it is important for polymer flooding to study the formation mechanism of polymer well plugging and find the chemical method to prevent blocking.By separating the blockage,it was found that the main components of the blockage were sand,dirty oil and volatiles matter including water.Four components and corresponding elements of separated crude oil and reference crude oil were analyzed.The results show that the average structure of asphaltene in the plug is not significantly different from that of asphaltene in crude oil.Therefore,it can be ruled out that the formation of plug is not the selective adsorption of asphaltene on sand surface.In order to further analyze the formation mechanism of blockage,this paper researched on the interaction mechanism between polyacrylamide and sand.Firstly,the properties of polyacrylamide were studied.The difference between nitrogen and hydrogen between the separated polymer and the polymer before polymer injection was obvious.It indicated that the molecular structure of the polymer changed during oil displacement.It should be that part of the acylamino group was hydrolyzed into negatively charged carboxylic acid group,which could be adsorbed on the surface of sand and stone causing a blockage.This paper also researched the agglomeration and sedimentation of polymers by metal ions.It was found that trivalent ions had strong agglomeration and sedimentation.Then the related properties of sandy soil are studied,and the basic components of sandy soil are obtained.It should be that part of the acylamino group was hydrolyzed into negatively charged carboxylic acid group,which could be adsorbed on the surface of sand and stone causing a blockage.Zeta potential experiment of sandstone pro ves that Ca²⁺can effectively reduce Zeta potential of sandstone,which is beneficial for carboxylic acid group with negative charge adsorbing to the surface of sandstone.Considering the salinity of formation water,it further supports that the formation of blockage is caused by selective adsorption of polymer.Therefore,in the follow-up research,the interaction between sandstone and polymer was further studied,including the wettability of polymer solution to sandstone,and the aggregation of polymer to sandstone.Simulated formation temperature and the polymer hydrolyzed at 65℃,and the comparative experiment was carried out.The results show that there is a stronger interaction between the hydrolyzed polymer and the sandstone,which can agglomerate the sandstone more easily.From the comprehensive experimental results,it can be inferred that the formation of the blockage is due to the hydrolysis of the polymer in the formation to form more carboxyl groups,while the metal ions in the formation water reduce the Zeta potential on the surface of the sandstone,making the polymer selectively adsorbed on the surface of the sandstone;at the same time,the presence of high valence metal ions makes the polymer easier to agglomerate and precipitate,thus forming the blockage.