Development And Performance Evaluation Of Composite Gel For Killing Well Based On Xanthan Gum

In the process of underbalanced drilling,to balance the formation pressure and seal the upper drilling fluid and the lower oil and gas layers,the gel valve technology is adopted.The mechanical strength of the pure polymer gel cannot meet the requirements of the field application.Therefore,it is necessary to add toughening material to enhance the mechanical strength of the gel valve.After the completion of drilling,the gel breaker should be added to destroy the structure of the gel valve and the gel breaker flowback can be realized.Usually oxidative breakers are used for traditional polyacrylamide gels.During the breaking process,oxygen is continuously generated and enriched.It is easy to cause explosion when mixed with natural gas.The gel glue valve made of biopolymer utilizes bio-enzyme as the glue breaker,while ensuring the safety of the glue breaking process,it could be naturally degraded and had no pollution to the environment.For this reason,xanthan gum was used as polymer,chromium acetate as crosslinking agent,starch,nano-silica and montmorillonite as toughening materials to prepare composite gel.HAAKE rheometer,Texture tester,pressure test device and adhesion test device were used to characterize the rheological properties,compressive stress-strain properties,pressure resistance,also the relationship between adhesion strength and the addition of toughened materials.The enhancement mechanism of composite gel was studied by scanning electron microscope and Fourier transform infrared spectrum,which provided the basic theory for the application of the composite gel in the field.The results showed that xanthan gum with a relative molecular mass of 18 million was more suitable for preparing high-strength xanthan gum composite gel.After adding starch,silica nanoparticles and montmorillonite into the xanthan gum-chromium acetate cross-linking system,the viscoelasticity of the composite gel was increased significantly.The viscoelasticity of the composite gel with silica addition was optimal.The elastic modulus of the composite gel reached 14740 Pa,the viscous modulus was 1933 Pa,and the elastic modulus was much larger than the viscous modulus,which showed an elastic solid behavior.The compressive strength of the composite gel increased first and then decreased with the increase of the amount of toughened material.When the amount of silica was 7 wt%,the compressive strength of the composite gel reached the maximum112545.1 m N.After adding three toughening materials,the adhesive force of the composite gel increased significantly,and the adhesion force of the 5 wt% silica xanthan gum composite gel was 40842 m N.After adding 10 wt% montmorillonite,the compressive strength of 300 m composite gel reached 105.5 MPa.The composite gel formulation with the best performance was 3 wt% xanthan gum +0.4 wt% chromium acetate +10 wt% montmorillonite.The three toughening materials enhanced the mechanical properties of the composite gel in a physical way.Starch granules were mainly attached to the crosslinking point and pore wall of the composite gel network by physical adsorption,and nano-silica was attached to the network structure of the composite gel by agglomeration.After adding montmorillonite into the gel,xanthan gum was intercalated into the lamellar structure of the montmorillonite.The starch-xanthan gum composite gel was broken by adding ammonium persulfate and xanthan gum enzyme respectively,and the breaking rate became faster after the xanthan gum enzyme was added.