Composite well cementing prepad fluid system and flushing method thereof

Abstract

The invention provides a composite well cementing prepad fluid system and a flushing method thereof. The system comprises an acidic flushing liquor, a chemical flushing liquor and a spacer fluid, which are pumped into the system alternatively. Acids in the acidic flushing liquor can react with calcium carbonate in mud cakes in drilling fluid on a shaft wall to generate calcium ions and carbon dioxide; the calcium carbonate particles in the mud cakes are decomposed, the mud cakes become loosen and can be easily washed off and peeled off, at the same time, generated calcium ions can promote thehydration reactions of cement slurry, and the two interface cementing quality is further improved. A surfactant in the acidic flushing liquor can enhance the flushing and washing effect on interfaces,the wetting property of the interfaces is improved, the penetrating effect on the mud cakes on the shaft wall is strengthened, and thus the mud cakes on the shaft wall can be easily washed off and peeled off. The chemical flushing liquor is used to remove oil films on the shaft wall, and isolates the drilling fluid from the acidic flushing liquor so as to prevent the drilling fluid from being polluted by the acidic flushing liquor. The spacer fluid can effectively isolate cement mortar from the acidic flushing liquor. At the same time, the spacer fluid can support calcium carbonate and clay particles that are separated from the mud cakes, and the safety of the well cementing construction is guaranteed.

Description

technical field [0001] The invention belongs to the technical field of oil and gas well cementing, and in particular relates to a composite cementing prefluid system and a flushing method thereof. Background technique [0002] In the oil drilling process, the mud cake is formed when the free water of the drilling fluid enters the formation during the filtration process, and the solid phase particles in the drilling fluid adhere to the well wall. After the drilling is completed, the residual drilling fluid and mud cake will affect the bonding strength of the cement sheath to the casing and the well wall during the cementing process. [0003] In cementing engineering, the interface between the casing string and the cement slurry becomes the first interface, and the interface between the cement slurry and the well wall becomes the second interface. The main reason for poor cementing quality at the cementing interface is that there is undisplaced drilling fluid and filter cake ...

AI Technical Summary

Problems solved by technology

Therefore, the main factor affecting the failure of the cementing interface is the existence of drilling fluid and filter cake, which makes the oil well cement-mud cake-formation unable to achieve integral solidification, which leads to a serious decrease in the cementing interface bond strength

[0004] The flushing fluid is usually mixed with surfactants, oxidants or diluted with drilling fluid. However, the traditional flushing fluid has a weak ability to wash away the drilling fluid mud cake and cannot efficiently clean the drilling fluid on the well wall. , it is impossible to effectively remove the thin, tough and dense mud cake formed on the well wall

Images