1． Development of cementing slurry system

1.1 .Ultra high density cement slurry

According to the theory of tight packing, ultra-high density cement slurry with a density range of 2.60-3.10g/cm³ was developed in the laboratory. Through reasonable deployment of weighting materials and particle size optimization, the pump ability and stability of cement slurry were coordinated and unified. The field application density was up to 2.72g/cm³, which solved the problem of ultra-high pressure cementing.

1.2 .Ultra low density cement slurry

In view of the difficult problem of cementing in low-pressure and leaky formation and long seal solid section, the objective of minimizing the accumulation void ratio of spherical particles with different particle sizes and improving the solid phase in unit volume of cement slurry is realized by using reasonable particle grading, which effectively improves and improves the comprehensive performance of cement slurry and forms a denser cement stone. The developed ultra-low density cement slurry has the advantages of high compressive strength and rapid development of cement paste, easy to adjust the thickening time of cement slurry, anti channeling and anti leakage, which is beneficial to resist corrosive fluid and increase the sealing quality. The minimum density of field application is 1.10g/cm³.

1.3. Cement slurry system with large temperature difference

Through the design of molecular structure and the mechanism of water loss reduction and retarding, a high temperature resistant water loss reducing agent and a large temperature difference retarding agent were developed, which solved the problems such as the poor ability of water loss reducing agent to resist high temperature and salt, the narrow range of temperature difference for the retarding agent, and the poor stability of the slurry under high temperature. Based on a series of additives with high temperature and large temperature difference resistance, four sets of cement slurry systems with large temperature difference suitable for different temperature ranges (50-120℃, 80-180 ℃, 90-190℃, 70-180℃) are formed through the optimization design of close packing theory. The system has a wide range of applicable temperature, wide range of applicable temperature difference and rapid development of cement slurry column top strength, which is conducive to ensuring the cementing quality of deep well long sealing section with large temperature difference. In recent three years, PetroChina has promoted the application of more than 1000 wells.

1.4 . Salt resistant latex cement slurry and supporting additives

In view of the technical problems of high-pressure channeling prevention, salt gypsum layer and salt water layer cementing in complex formation, through the design of latex particle structure and the use of special emulsifier system, the problem of latex stability in salt water and high price ion cement slurry was solved, and the salt resistance of cement slurry reached saturation. Latex can form film in cement, increase gas channeling resistance and improve the anti channeling performance of cement slurry. At present, the latex is resistant to 15% calcium, 30% salt and 180℃.

1.5. Ductile cement slurry

Based on the study of the toughening mechanism of cement stone, the stress model of cement ring is established. On the basis of improving the mechanical properties of cement stone, the developed cement series toughening materials can ensure the construction safety and meet the needs of annulus sealing, forming two sets of ductile expansion cement slurry systems, i.e. medium temperature (30-100℃) and high temperature (100-200℃). The application scope of ductile expansion cement has been extended from gas storage well to shale gas and tight oil and gas well cementing.

1.6. Anti CO²corrosion cement slurry

The underground acid gas will corrode the cement sheath in humid environment, which will reduce the compressive strength of cement stone and increase the permeability, so as to shorten the production life of natural gas wells. Aiming at the problem of cementing in high CO²gas field, the anti- CO² corrosion material was developed, and the anti-CO²corrosion cement slurry system with high temperature (70-180℃) and medium temperature (< 70℃) was formed. The comprehensive cost of the system is low, and the anti-corrosion effect is good, which can effectively guarantee the long-term sealing performance of cement stone under the condition of rich CO.

1.7. Phosphate brine mud

The phosphate cement slurry system was developed in combination with the matched water loss reducing agent and retarder, which provided a new technical way for cement ring anti-corrosion and cementing under high temperature in CO² environment. The cement slurry has good fluidity and channeling resistance, rapid development of compressive strength, good slurry stability and water loss control effect. The thickening time can be adjusted within the range of 50-150℃, with good comprehensive performance. At present, two wells have been tested on site.

1.8. Self repairing and self-healing cement

In order to solve the problem of gas channeling or annulus pressure after well cementation, the research of self repairing and self-healing cement has been carried out in recent years. The expandable core-shell polymer repair agent developed has a temperature resistance of 150℃. The repair agent has the structure of "core-shell" microcapsule, and the double functions of expansion and adhesion. According to the different underground environment, one or two of the effects of activating the expansion and adhesion of the repairing agent play a role at the same time. The repairing agent has the repairing ability to the broken cement stone and has no effect on the construction performance of the cement slurry.

1.9. Low hydration heat and low temperature cement

The main difficulties of cementing in deep water are low temperature on the surface, narrow safe density window, easy pressure leakage of formation, potential shallow water channeling or gas channeling problems, and high requirements for short-term and long-term sealing of annulus. Low density, short transition time, rapid development of compressive strength and low hydration heat in mud line are the requirements of cement slurry system. In recent years, great progress has been made in the laboratory research of deep-water low-temperature cementing slurry system. The hydration heat is more than 35% lower than that of ordinary cement, and other comprehensive properties meet the requirements.