Effect of Sugar on the Thickening Time of Cement Slurries

Abstract

Abstract Sugar is widely recognized as a cement retarder by the drilling industry and has been used in cementing operations where cement returns are expected on surface. Experts disagree about the effect that sugar has on cement slurries, a few believe that it acts as both an accelerator and a retarder depending on the concentration, but the majority believe that the sugar acts as a retarder only. Lab tests of thickening time and compressive strength were conducted using different concentrations of sugar. The results indicated that the sugar acts as a retarder of cement slurries when added in small concentrations and as an accelerator when added in high concentration. The compressive strength tests showed that the accelerated slurries developed very little or no compressive strength, indicating that no hydration of the cement grains occurred. The retarding mechanism of the sugar is well documented, but the acceleration effect is not widely known. An attempt was made to explain the mechanisms involved in the shorter thickening time and lack of compressive strength observed at high sugar concentrations. These project findings are of great practical importance to the drilling industry. Sugar is currently used in the field with the idea that it will always retard the slurry. Introduction The author's own experience, while working for a cementing service company, includes the following uses of sugar in the field during well cementing jobs:In Lake Maracaibo, in a zero discharge environment, cement returns were sent to a 25 bbls container or a cistern that already had 1 to 5 bbls of water with 5 Kg (around 0.45 lb/bbl) of sugar in it. The idea was to keep the cement returns liquid for a couple of days until the containers could be sent to land for proper disposal.On land jobs granular sugar (not measured) was added to the cellar on top of lead cement slurry that returned to surface. A top job was going to be done, with good quality tail cement slurry, immediately after the primary job was concluded and the idea was to keep the cement on surface liquid to allow time to pull the tubing after the top job was done and avoid it from being cemented up.The other main cementing service companies have similar applications. From information given to the author from different service companies there are discrepancies between the recommendations of the concentration of sugar used currently in the field in order to retard cement slurries. Schlumberger recommends the use of sugar in a concentration of around 5 lbs of sugar/ bbl of cement slurry.3 BJ Services uses sugar as a retarder in concentrations ranging from 10 to 20 lbs of sugar/bbl of cement slurry.2 Halliburton Energy Services uses 5% BWOW (by weight of water) of sugar as a concentration to delay the set of cement. This concentration of sugar is added to the water and then mixed with the slurry; it is equivalent to 10 lbs of sugar/ bbl of slurry.8 In all these applications sugar is used only as a retarder; however there is some evidence of other effects.