Results of cement-to-rock contact study
- 1 — Saint-Petersburg Mining University
- 2 — Jilin University
The paper focuses on the problems of oil and gas well cementation. It has been established that the main reason why formation fluids leak behind the casing is due to poor isolation of the annulus caused by incomplete cleaning of the filter cake, which results in weak or absent adhesion between the cement and the rock. The authors demonstrate that adding polymer modifier GM-II to the spacer fluid strengthens the cement-to-rock contact by several times. Moreover, mixing spacer with cement slurry does not degrade such important properties as spreadability and consistency of the latter. The paper contains investigation results on the content of polymer spacers that improve cementation quality of oil and gas wells. Spectral infrared and X-ray analysis allowed to define the impact of phase composition and mineral structure of the system «cement stone-filter cake-formation rock» on improving leak tightness of the annulus. Electron microscopic study showed that the use of polymer spacers facilitates formation of felted net-like structures between hydrated minerals. The composition of these structures, binding cement grains and clay minerals, has been studied by means of energy dispersive X-ray microanalysis. Obtained results allow to come to the conclusion that these structures mostly consist of hydrated calcium silicate (more than 77% by mass), which agrees well with the findings of infrared and X-ray analysis. Pilot tests, performed at the Shengli oil field in China, have confirmed efficiency of developed spacer fluids.