Development And Evaluation Of Device Measuring Coagulation Process Cement Slurry Volume Change

When cement system goes into solidification stage, the absolute volume caused by matrix is reduced, the molecular volume of the reaction products are always smaller than that of the reactant volume and the water, this is known as cement chemical shrinkage, the volume shrinkage rate of the ordinary Portland cement can reach5%～6%.Cement volume contraction can cause an effective on column pressure, on the other hand, because the gel suspension to prevent the slurry, according to the principle of minimum energy of cement stone will happen to racial shrinkage casing, cementing interface will appear at the section of micro annulus, it may lead to gas channeling.At home and abroad for cement paste volume expansion and shrinkage properties mainly depend on the evaluation method evaluation instrument, but these methods have some drawbacks, during the whole period of continuous determination of changes in experimental conditions of cement plastic body and hardening volume production with time, it can’t meet the demand of further study.In this paper, the volume change of cement slurry simulation evaluation device based on previous practice, the high temperature, high pressure cement slurry volume expansion and shrinkage simulation device has carried on the overall structural design, the kettle system design, wellbore simulation system design, control system design, measurement system design and other auxiliary system design, and manufacturers together a device for processing, has conducted tests on sealing performance, temperature control, pressure control. The equipment realizes the formation temperature (room temperature to130℃), pressure (0～80MPa) simulated downhole conditions.By expanding the preliminary evaluation proved shrinkage performance of different system of cement slurry volume, all aspects of the device performance is good, have basically reached the design requirement, the equipment can be in stimulating the formation environment, on the basis of different well conditions, in variable temperature and pressure conditions set, automatic and continuous measurement of cement slurry from the liquid to the plastic body again, to the whole process of hardening body volume change with time and at the same time monitoring of cement hydration heat. And the different cement slurry system for the volume expansion and contraction evaluation, experimental effect on the cement hydration process and the factors with expansive cement slurry system agent were evaluated, draws the following conclusion:(1)The water cement ratio is an important factor affecting the volume shrinkage of cement slurry before initial setting, with water-cement ratio increases, the plastic stage time, initial and final setting time delay, early coagulation volume shrinkage;(2)Temperature is an important factor affecting the cement hydration rate, with the increase of temperature, the initial setting time of cement slurry and the final setting time gradually shortened, and the higher the temperature, the faster the hydration rate of cement is, more uniform particle size distribution of cement slurry, interfacial hydration reaction more quickly, resulting in the initial and final setting time to shorten the interval; as the temperature increases, the greater the volume shrinkage of cement and the final setting time are;(3)Cement with foaming agent KQ in plastic stage, cement slurry by chemical gas can play compensation cement slurry volume loss, delay the pore pressure decreases effect, even in the50MPa under the condition of high pressure, with cement slurry2%KQ foaming agent could markedly reduce the volume before the initial setting shrinkage;(4)Slurry with a lattice expansion cement agent, the expansion is mainly caused by crystallization later produce crystallization pressure, promote the macroscopic volume expansion of cement, cement slurry early plastic shrinkage of volume did not significantly improve, pore pressure cannot volume shrinkage compensation cement slurry decrease, this can be of no use to the early period of gas channeling prevention.