Develpment And Performance Of Polymer Nano/Micro Composite Hydrogel For Well Killing Application

During the processes of underbalanced drilling,completion and workover,composite gel is applied as gel valve to realize well kill successfully through balancing formation pressure and pluging the wellbore to prevent oil and gas leakage.Gel valve mainly relys on mechanical strength and adhesion with wellbore to complete well kill.Therefore,it is the key to characterize the mechanical strength of composite gel and to quantitatively study its adhesion force with contacting substrate.In this paper,nano/micro particles including nanosilica,starch and montmorillonite?MMT?are introduced to enhance the strength of composite gel.Electronic universal testing machine,rheometer and compression testing device are performed to study the influence of the addition of particles on mechanical properties such as stress-strain,viscoelasticity and compressive strength of the composite gel.X-ray diffraction?XRD?,fourier transform infrared spectroscopy?FTIR?and differential scanning calorimetry?DSC?are carried out to study the interaction between enhancer particles and polymer.On the basis of the above interaction analysis,environmental scanning electron microscopy?ESEM?and transmission electron microscopy?TEM?are adopted observing the distribution of enhancer particles and the microstructure of composite gels to further reveal the enhancement mechanism of particles on composite hydrogel.The results showed that nano-silica could significantly improve the mechanical strength of composite gel.Compared with the conventional gel without silica,the viscoelastic moduli of composite gel with the silica content of 10wt%was increased by three orders of magnitude,and the compression strength was also increased from 70.8kPa·m^-1 to 196.64 kPa·m^-1.The as-prepared composite gel was compressed to irreversible or reversible deformation as compared to cracking of conventional gels without silica.The addition of starch also contributed to the improvement of mechanical strength for composite gel,and the resulted starch composite gel displayed excellent dynamic restructure ability.The composite gel with starch content of 10wt%could restore to its initial viscoelastic value within 3600s after suffering a high oscillation stress of 1000Pa for 60s,with a strain just of 0.00097.The hydrogen bonding between starch and polymer chains prompted their interaction thus the starch particles were able to enhance the macro properties of the composite gel.In view of the silimar enhancing mode from nano-silica and starch,a mechanism of?adsorb-fill?was proposed to illuminate the enhancement according to the distribution of nano/micro particles of silica and starch in the three-dimensional network of composite gel.Such?adsorb-fill?mechanism stated that most of the particles selectively adsorbed onto network skeleton,inducing the enhanced network of gel to present stable hexagon,meanwhile a small part filled in the network pores,decreasing the network porosity,which distributing mode enhanced the microstructure of composite gel,and thereby improved the macro performance of composite gel.MMT was also introduced to improve the macro mechanical properties of composite gels.The way of interaction between MMT and composite gel was strongly dependent on the concentration of MMT.When the concentration of MMT lied between 1wt%and 3wt%,MMT dispersed in the composite system in the form of exfoliation.With the concentration increasing to 5wt%,a specific proportion of MMT was intercalated by polymer chains,also the interlamellar spacings of MMT enlarged.While the concentration of MMT continued growing to 7wt%,MMT was mainly exfoliated blending with the polymer chain.We self-designed a set of device and method for adhesion force measurement with the assist of texture analyzer.The adhesion force between composite gel and different contacting substrates was investigated,and the relationship of compression strength for composite gel with its own mechanical strength and adhesion force was also investigated.It was found that the peeling adhesion was affected by the enhancer particles and the texture of contacting substrate.Compared with MMT and starch,the nanosilica composite gel presented the largest peeling adhesion with substrates.The adhesion of composite gel with stainless steel and polymethylmethacrylate?PMMA?was stronger than that with teflon.Mechanical coupling,wettability and molecular interaction between two mutual adhesive substances were applied for explaining the adhesion mechanism.In addition,the compression strength of composite gel was found a collective effect of mechanical strength and adhesion of gel.When the adhesion with wall of tube was strong,the compose gel with relatively low mechanical strength was fractured through internal bubbling,while the composite gel with increasing strength would be broken as a result of gas channeling or gel being peeled from the wall of tube and moving upwards as a whole bulk.