| The paper analyzes firstly the types of annular flow and the factors systematically, points out six key processes of cementing job that have critical effects on cementing quality. After analyzing the latest developments on the annular flows and their factors, the paper finds out its main researching focus: the mechanism of cement slurry weight-loss during its setting.In order to study the mechanism with weight-loss experiments, the paper, after analyzing the static setting properties of down hole cement slurries, develops a new method to measure the gel strength of setting cement slurries: continuously measure with undestroyed slurry structures in a static setting environment, and a new device that measures the gel strength before initial set truly and continuously at a very low shearing rate. Also, the paper equips previous cement slurry column pressure measuring device with heating barrel, higher column and accurate pressure gauge.In order to understand weight-loss much better, the paper carries out a large numbers of weight-loss experiments. The experimental data show:1) The gel strength correlate initial set very well, so the initial set can be determined by the development of the gel strength directly.2) During the setting process (before initial setting), the relationship between the pressure and the gel strength is not a linear but a staged function composed of two proximate linear with different slope.3) The stabilities of cement slurry can influence its weight-loss badly. More stable the slurry is, less filtration and free water, higher effective column pressure it can remain during its setting, which is helpful to control the formation fluids and prevent annular flow caused by formation fluids invasion during waiting-on-time.4) The time for cement slurry column pressure to drop to water column pressure, influenced by the stabilities and componentive properties of cement slurry, is not always ahead of initial set. It is unreasonable that the water column pressure time is ahead of, after or at initial set.5) Increasing the setting stability or the filtration control ability all can improve the weight-loss, which confirms the commonness of the two cement slurry properties that can be unified on a certain degree.With the large numbers of experimental data and experimental phenomenon, the paper finds out and confirms the limitations of previous cement slurry weight-loss mechanisms, also the causes of the limitations, which can provideiimportant reference information for the paper to study the mechanism ulteriorly.Because of the physical and chemical sorption between the cement grains, water molecules, and additive molecules, the grains and their outer water film constitute a new kind of system grains. The grains constitute the system as elementary structure unit, control the free water, thixotropic properties and the filtration of the system. This is the microstructure model of cement slurry system developed by the paper: "megranate kernel" cement slurry microstructure model. The model accounts for the setting stability, filtrate controlling, thixotropic properties of cement slurry, the relationships between the properties, and the numerous weight-loss phenomenon reasonably, which verifies the model's validity and provide a messiness base for the further studying on the weight-loss mechanism from microstructure angle.The outer water film can transport its weight to the bottom hole by its slipping and shaping, so, though suspension weight-loss lies in the beginning of cement slurries' setting stage, but it is not the cement slurry itself but its skeleton structure that is suspended, and when the skeleton structure can support itself in the equivalent fluid by the suspension force, the skeleton suspension weight-loss is over. Since then, the cement slurry and the two surfaces form a single-direction isolated flexible hydraulic pressure system, the cement slurry enters the volume shrinkage weight-loss stage that will last to the initial setting. The new mechanism takes into...
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