Preparation Of Temperature-responsive Shape Memory Materials And Research On Its Mechanism Of Loss Prevention And Plugging

The Lost circulation of drilling fluid will greatly increase the non-production time of oil and gas wells and the cost of comprehensive well construction.It is a global problem in drilling engineering that has not been well solved.Although the traditional inert bridging material still occupies the main position of lost circulation material on the oilfield due to the variety and inexpensive characteristics.Meanwhile,there is a shortcoming of weak deformability that leads to a limited application.In this paper,the prepared one-way/two-way shape memory intelligence materials have developed a shape memory lost circulation material with temperature-sensitive expandable/reversible expansive characteristics.The comprehensive performance is systematically evaluated,and its mechanism of loss prevention and plugging preocess is revealed.First,a series of thermosetting one-way shape memory epoxy resin materials are synthesized by epoxy resin E51 and 4,4’-diaminodiphenylmethane(DDM)and hollow glass beads(HGB)through high temperature cross-linking curing reaction.A temperature-sensitive expandable shape memory lost circulation material SMP-LCM with adjustable response temperature,and expansion rate is prepared.Infrared analysis shows that the active hydrogen in DDM and the epoxy group in E51 undergo a ringopening reaction to complete the curing.HGBs are inertly filled to provide compressible pore space.The dynamic thermomechanical analysis shows that the internal molecular chain of the material will transform from a glass state to a rubber state during the heating process.The shape memory test shows that the shape fixation rate of the material is close to 100%,and the shape recovery rate is greater than 90%.The response time will decrease with the increase of temperature;The efficient recovery of the internal compressed space driven by the entropy elasticity of the internal molecular chain after thermal excitation results in the macroscopic volume expansion.The material expansion rate is2.58%～125.50%,and has a good correlation with the amount of HGB.Thermogravimetric analysis shows that the initial decomposition temperature of the material is greater than 230 ℃ indicating good thermal stability.Plugging experiments show that SMP-LCM has a good sealing effect on large-porosity sand beds and sand discs,and the bearing pressure of the sealing layer can reach 5MPa.Before SMP-LCM is activated,it can pass through the narrow downhole channel and enter the depth of the loss layer with a small volume.When activated at the formation temperature,the volume expands and elastically adapts to the loss channel and forms a tight pressure-bearing sealing layer,to strengthen the wellbore effectively without tripping after the loss occurs.Secondly,two-way shape memory poly(acrylamide-propylene)cross-linked hydrogels are synthesized by free radical polymerization with acrylamide(AAm)and acrylonitrile(AN)as functional monomers and N,N′-methylenebisacrylamide MBA as a cross-linking agent and potassium persulfate as initiator.A temperature-sensitive reversible expansion shape memory lost circulation material UCST-LCM is prepared.Infrared analysis shows that the monomers are successfully polymerized;shape memory tests showed that the molar ratio between AAm and AN and the MBA cross-linking agent ratio are the main controlling factors for the reversible swelling performance of the hydrogel.When the monomer molar ratio is 0.50-0.65 and the cross-linking agent content is 1.5-3.5%,the hydrogel has the best reversible expansion performance under high-and low-temperature cycles of 20-90 ℃.The reversible swelling rate can reach 24.06%,and the response temperature is 64.61-97.84 ℃.When the temperature is high,the hydrophilic effect of the hydrogel enhances the extension of the internal molecular chain and swells by water absorption,and the hydrophobic effect enhances the molecular chain curling and drainage shrinkage when the temperature is low;the viscoelastic test shows that the storage modulus of the hydrogel is always higher than the loss modulus,showing solidlike characteristics,and has a wide linear viscoelastic region and high critical stress and strain;Scanning electron microscope observation shows that the hydrogel has a large number of three-dimensional pore structures with an average pore size is 5.70 μm;thermogravimetric analysis shows that the hydrogel decomposition temperature is greater than 251.18 °C;UCST-LCM has a good salt resistance,and can significantly reduce drilling fluid medium pressure and high temperature and high pressure fluid loss and improve filter cake quality;The plugging experiments of the visible sand bed and the high temperature and high pressure sand disc filtration apparatus show that the UCST-LCM has a good effect of reducing permeability.When circulating to the lower well section at high temperature,UCST-LCM swells to help elastically squeeze into the lost pores and fractures to form a low permeability sealing layer.When circulating to the upper well section with low temperature,UCST-LCM drainage shrinks to help pass the vibrating screen to truly improve the lost circulation effect while drilling.In summary,this paper has carried out a certain exploration and research on the application of temperature-responsive shape memory materials in the field of lost circulation.The research ideas and methods formed and the results obtained have a certain reference value.It is expected that it will be helpful for the further research and development of the follow-up intelligent lost circulation materials.