Technical Research And Application On The Anticorrosion Cement Slurry System

Cement Rock is liable to be corroded and its properties could be changed when in a sour environment, which will cause it to lose isolated capability, accordingly lead to annulus gas migration even entire well scrap. This scenario will cause great economic loss. For example, corrosion from CO₂ will reduce the compression strength and increase the permeability rate of the cement rock, forming an access for gas migration. Ferric aluminate is more likely to be corroded by H₂S. Cement Rock could disintegrate for volume expansion of ferric aluminate and aluminate after being corroded by H₂S for three months. Cement with the compression strength and permeability rate measures up to API recommendation will be seriousely corroded by liquid rich in CO₂ in several months. H₂S is an extremely toxic substance, soluble in water. The ionization constant of H₂S lower than H2CO3. When CO₂ exists in the corrosion medium, the ionization constant of H₂S becomes higher, making all hydration products of cement rock appear alkalescence. Thus, it can destroy all composition of cement rock.In order to solve corrosive problem in cementing, we developed to special study according to the actual formation condition in northeast of Sichuan oilfiled. Research has been carried out on the corrosion mechanism and influencing factors caused by CO₂ and H₂S through performance compare test before and after corrosion with high temperure and high pressure and content of two type gas. The test content include: CO₂ corrosive rule for cement rock, H₂S corrosive rule for cement rock and both contain H₂S and CO₂. Based on the research result, develop DC200, DC206 and so on anticorrosion additives and technique which can effectively prevent CO₂, H₂S or other gases to corrode down hole cement, also to improve the anticorrosion capability of cement rock and cementing success. Lab test evaluation proves that the additives produced have relatively good anticorrosion capability, which will help extend the production cycle of wells and improve economic efficiency.Now the additives and relative technique have been utilized to cementing operation for three wells. Cementing quality are all beyond bond qualified.