Research On Synthesis Of CO₂-sensitive Hydrogel With High Strength And Application Of The Self-healing Cement Slurry By CO₂-triggered

Annular air channeling is the phenomenon of gas through the poorly cemented interface and cementing micro-fracture channels after well completion.It is an important technical problem of the wellbore.Because it can damage the integrity of the wellbore and affect the quality of cementing.Meanwhile,it poses a great threat to the safety of drilling and production when the toxic gases(CO₂,H₂S,CO,etc.)through the micro-fracture.Therefore,it is of great significance for petrochemical industry to develop a sealing material that can respond to toxic gas after cementing in underground oil field.It is a common technique to block the channeling channel by using polymer materials with responsiveness to underground oil or water in oilfield engineering,but there are lots of shortcomings of technical in the material system.For example,due to the lack of good responsiveness to natural gas,the self-repair of micro-fracture channels cannot be realized.Then,the subsurface small molecular salts have serious damage to the mechanical properties and responsiveness of materials,it will seriously affect the plugging effect.Above all,the material lacks the specific response performance to the underground associated toxic gas,and the toxic gas channeling is easy to lead to lots of accidents.Therefore,a high-strength hydrogel with good sensitivity to CO₂or H₂S is designed and prepared in this paper as a blocking material for channeling micro-fracture.The hydrogel can convert into amphoteric polyelectrolyte hydrogel by CO₂or H₂S to enhance the salt resistance and at the same time to seal the microfractures of the cement column and improve the integrity of the well.The specific research contents of this paper are as follows:1.In our study,chemically cross-linked hydrogels were synthesized by the solution polymerization of acrylamide,acrylic acid,and 2-(dimethylamino)ethyl methacrylate(DMAEMA)with NMBA as cross linker.The mechanical strength of the hydrogel(Cu-PMAD)was significantly improved by complexation between Cu²⁺and the carboxyl group of the hydrogel network.The tensile strength and the fracture strain of the hydrogel is up to 0.65 MPa and 420%,respectively.2.The tertiary amine group of DMAEMA unit in the hydrogel is protonated to form quaternary amine salt with positively charged by CO₂or acidic conditions.Meanwhile.the hydrogel is transformed from anion hydrogel to amphoteric polyelectrolyte hydrogel.The salt resistance of the hydrogel is provided by the anti-polyelectrolyte action of amphoteric polyelectrolyte hydrogel.The hydrogel can swell further through amphoteric structure under CO₂of nature gas and small molecular salts conditions.Meanwhile,the tensile strength and the fracture strain of the hydrogel in 1.0 mol/L saline solution can up to 0.3MPa and 360%.3.The CO₂-triggered self-healing cement slurry is prepared by mixing Cu-PMAD hydrogel powders with cement.The strength of cement stone is reduced with the addition of hydrogel powders,but the toughness of cement is increased.The thickening and water-loss performance of cement slurry can reach the requirements of field application.The experiment of CO₂-induced microcrack plugging and repairing of cement stone shows that the cement stone with hydrogel can repair the microcrack by the triggering of CO₂.The maximum anti-channeling pressure of cement stone can reach 1.94 MPa.However,the self-healing performance of cement is cannot achieve by N₂and its maximum channeling pressure is only 0.32 MPa.The self-healing performance is attributed to the amphoteric structure of hydrogel triggered by CO₂due to the DMAEMA unit of the hydrogel was protonated.