Recipes of cement slurries for sealing casing in deep wellbores

Abstract

The authors of this paper discuss issues connected with the sealing of deep casing columns. The results of analyses of cement slurry recipes recently used for sealing wellbores in Poland have been presented. Laboratory experiments were performed on samples at temperature 90–120 degrees of Cesius and pressure 60–70 MPa. Recipes of slurries were worked out at the Oil and Gas Institute Section in Krosno and Cement Services (EXALO group). Slurries were based on 10% NaCl brine with such additives as: – 20–25% of latex (prevents gas migration and lowers filtration); – silica powder (increases thermal resistance of hardened cement slurry at high temperature); – hematite (weighing material: 30–110% of cement mass); – microcement (sealing up the cement matrix). The G type HRS drilling cement, meeting standard ‘PN-EN ISO 10426-1 »Oil and gas industry« – Cements and materials for cementing wellbores’, was used as a binder. The density of the presented slurries ranged between 2050 and 2350 kg/m$^{3}$, plastic viscosity a hundred or so mPa·s and thickening time from 3.5–6 hrs. The filtration of slurry oscillated between 30 and 40 cm$^{3}$/30 min, with zero water settlement. The compressive strength of hardened sealing slurries was high (frequently over 30 MPa). The detailed analyses of slurries and hardened cement slurries as well as works on the improvement of recipes, resulted in the systematic improvement of the quality of cementing jobs on production casing in deep wellbores on hydrocarbon deposits.