Soap-Free Latex Cement And Preflush Research Enhancing The Interface Cementing Strength

The interface cementing strength in well cementing is closely related to zonal isolation capabilities which is an integrated problem related to the production safety, efficiency of resource development, economic benefits and ecological environment protection. Enhancing or improving the interface cementing quality is a systematic project, which needs to study the performance of different working fluids and the performance of the interaction of these fluids during the drilling and well completion. If study a single working fluid, it is difficult to improve the interface cementing quality. In this paper, three working fluids as a whole including the drilling fluid, preflush, and the cement slurry, were researched the influence of the interface cementing quality by a way of the longitudinal system.A soap-free latex was synthesized utilizing the ionic comonomer (AMPS/NaSS) and can be used in the oil well cement system. The code of the soap-free latex is ASL? ASL soap-free latex has good emulsion stability, film-forming properties and thermal stability. The chemical composition and microstructure of ASL soap-free latex were analyzed by using infrared spectroscopy and transmission electron microscopy methods. Compared with the THD-818 commercial latex and the NSL traditional latex, ASL soap-free latex without stabilizer have a good ion stability.When the dosage of AMPS/NaSS was 1.3%?1.9%, the compressive strength and the cementing strength of ASL soap-free latex cement were higher. ASL latex cement using the right amount of defoaming agent can improve the density of the cement slurry and the cementing strength of the cement stone. The suitable dosage of D50 defoamer was 0.8%. When the amount of ASL-13 latex was 10% to 20%, the latex grout had a good performance and the cement stone had high compressive strength and cementing strength. When the thickening temperature were 70? and 90? respectively, ASL latex grout had good thickening time curves. With the curing temperature (70??90?) increased or curing time (1 day to 15 days) increased, the compressive strength and cementing strength of ASL latex cement were increased.Used X-ray diffraction analysis and thermal analysis method to research the ASL-13 latex cement and the blank cement, the cement compositions of hydration products between the bulk cement and cementing interface were diverse. In the bulk cement, ASL-13 latex cement contained latex and more calcium carbonate, while the blank cement samples contained more calcium hydroxide. At the cementing interface, ASL-13 latex could suppress the growth calcium hydroxide crystals, and promote the growth calcium carbonate/ettringite (AFt) content and gels hydration products. These hydration products can improve interface cementing strength. The membrane-like substances were observed at both ASL-13 latex cement sample and THD-815 latex cement sample by using scanning electron microscopy. the surface roughness of ASL latex cement decreased significantly.The mechanism of ASL soap-free latex in oil well cement can be divided into two aspects:Firstly, in the cement slurry, the traditional latex adsorbed on the surface of cement particles relying on Van der Waals forces between the emulsifiers and the cement particles. The ionic bond was formed between the ionic groups on the ASL soap-free latex and the cement particles. The ionic bond was formed ionic bond was formed between the ionic groups on the ASL soap-free latex and the crystal surface. The growth of crystal was changed because of the steric hindrance, so the volume of these crystalline hydration products was decreased. Secondly, at the cement stone, the ionic bond was formed between ASL latex membrane and cement interface, while the emulsifiers were populated between traditional latex membrane and cement interface. So the soap-free latex cement exhibited higher compressive strength and cementing strength.A biphase preflush was prepared, which has good pre-cleaning ability for a variety of drilling fluid. The preflush had good thermal stability, rheology and suspension stability at room temperature and high temperature. The preflush mixed with drilling fluid and cement slurry had good compatibility and stability. When both biphase preflush and ASL latex cement were used, the interfacial cementing strength was the highest.At the interface, the silica fume and slag in the biphase preflush take place hydration reaction with cement, consume calcium hydroxide,and the crystalline class products with expansion increase. Using both biphase preflush and ASL latex cement, a large crystalline substances and gel materials generate at the interface to enhance the cement quality.These results illustrate that ASL soap-free latex cement has good performances. When both biphase preflush and ASL latex cement are used, the interfacial cementing strength could improve significantly which can improve the zonal isolation capacity of the cement sheath and the cementing quality.