Change of early compressive strength under the influence of selected agents improving sedimentation stability

Low density cement slurries are the most commonly used formulas for sealing casing pipe columns in conditions of reduced reservoir pressure or in low-density zones. Appropriately reduced cement slurry density allows the hydrostatic pressure of the cement slurry to be reduced, so that there is no risk of cement escaping into areas with poor compactness. Lightweight cement slurries can be also successfully used for sealing deep wells, where it is necessary to press the cement slurry to a great depth. Two recipes are used in such a case: the first cement slurry is lightweight slurry, followed by a cement slurry of higher density. In order to reduce the density of the slurry, various types of light fillers are used, whose presence in the slurry reduces its density. However, when lightweight filler materials are used, the slurry fractionates, which is manifested in the separation of light fractions in the upper part of the cemented annular or space between particular casing and settling to the lower parts of the heavy slurry fractions. In order to eliminate this undesirable phenomenon, agents are used which, due to the increase in the viscosity of the mixing water, followed by an increase in the structural strength of the stone, result in improved sedimentation stability of the developed cement slurry recipe. However, the presence of these agents changes the value of early mechanical strength formed from the cement slurry sheath, and this parameter is particularly important for this type of cement slurries. In addition, antisedimentation agents cause a change in the cement slurry setting time, and this parameter is important from a technological point of view (adjusting the circulating time to the time necessary to carry out the cementing operation). Therefore, this publication discusses the issue of changing the value of early compressive strength under the influence of selected agents improving sedimentation stability. The article discusses the results of testing four types of agents that improve sedimentation stability. Tests were carried out for control cement slurries prepared on the basis of two types of cement, CEM I 42.5R cement and aluminum-calcium cement. The tests included mainly the thickening time, transition time from the value of the thickening start to the value of the thickening end and compressive strength after 24 hours of sample hydration. Based on the research carried out, the impact of agents improving sedimentation stability on the value of early compressive strength was determined