Cement systems for well cementation in gas fields with high pressure, high gas production rate and high sulfur concent

Key words:  "three　high" gas field  cementing  cement slurry  set cement  cement corrosion

Abstract:

In view of the cementing difficulties in high production gas wells with high pressure and high sulfur content (three high), related requirements for cement slurry were discussed. On the basis of the analysis of the cement corrosion mechanism, the antiseptic strategy for cement system in "three high" gas fields was proposed. An appropriate particle size distribution philosophy was used for different blending component of cement slurry to optimize the design of cement slurry formulation. Orthogonal experiments were conducted, and four kinds of formulation for two cement systems, the lightweight highstrength cement system and the fiberlatexmicrodilatancy cement system, were screened out with densely packed cement sheath and favorable corrosion prevention capability. In addition, evaluation tests on the corrosion resistance of set cement against H₂S and CO₂ were carried out, including the strength, permeability, loss in weight, corrosion depth and internal structure alteration before and after corrosion. The life span of set cement under corrosion was predicted in the light of the experimental data. The application results of Longgan gas field show that the qualification for cementing can be obviously improved by using the technology. Research results can be used to provide guidance for cementing in "three high" gas fields, and to prolong the life span of gas well.