Increasing the Frost- Resisting Properties of Cement Stone in Casing and Cementing of Wells Through the Use of Magnesia Cement Material

Abstract

Abstract In 2012 by request of JSC"TNK-BP Management", in the Scientific laboratory "Technological liquids for well drilling and casing" of the Perm National Research Polytechnic University (PNRPU) works on assessing the properties of the cement materials developed by three foreign and one Russian service companies were carried out. These blends were announced as the cementing materials that had been specially designed for oil and gas well casing and cementing in the areas of Western Siberia and the Far North, where the presence of permafrost (PFR) in well profiles have made their use more complicated. The received testing results of the presented cement slurry – stone indicate that the signs of failure in the samples being tested for frost resistance are first indicated after 2 to 4 cycles of freezing and thawing. The samples showed fractures, flaking or chipping off. The maximum number of the "freeze and thaw" cycles prior to decreasing of cement stone strenght in the most frost-resistant of the blends presented for testing was 5, which is not enough to be able to predict a long-term integrity of cement stone incorporated in casing and cementing of the well. To increase the quality of casing cementing within the intervals of permafrost rock formation, the employees of the PNRPU developed a new cementing blend with higher frost-resistance properties of cement stone. This special cement material is based on a highly active cementitious agent – magnesium oxide. The major advantage of this newly designed magnesia cement slurry is the higher frost resisting ability of cement stone as compared to those being tested. The reason for this is low capillary fluid content. The cement stone in such cementing material endures over 15 cycles of the "freeze" and "thaw" test. Among the positive characteristics of the cement slurry-stone which is viewed as perspective when used for casing cementing in the continuous permafrost zones are as follows: –possibility to achieve a lightweight cement slurry;–zero ice-thawing during putting the slurry into casing string annulus;–low rates on water separation and cement-water sedimentation of cement slurry;–good harden ability of cement slurry and strength development of cement stone at lower temperature;–adhesive bond formation between cement stone and ice. The achieved magnesia cement blend can be used for experimental and industrial testing during casing cementing, when the casing strings extend through the perennially frozen rock deposits.