Study On Evaluation Method Of Anti - Channeling Ability Based On Gypsum Performance

The phenomenon of gas migration during the cementing process, which affected the high pressure gas well cementing quality and safety seriously, is a potential problem that almost all gas well must be faced with, particularly in the Gulf of Mexico, Tarim oilfield, etc. It is the key technology to prevent the potential risk of gas channeling effectively that evaluating the anti-gas migration ability of cement slurry in the process of condensation accurately. Existing evaluation methods mainly take into consideration the prat performances of slurry, such as filtration, static gelling strength transition time and so on, ignoring the effect of the special condition of formation, casing, etc. and solving the gas migration ineffectively. Therefore, it is of great significance for preventing the gas channeling that studying the anti-gas channeling performances of plastic-state slurry and establishing a more comprehensive, integrated, stronger maneuverability new evaluation based on the existing.This thesis puts forward the key performance indicators for preventing the early gas channeling form the angle of cement hydration mechanism based on the overseas and domestic research status. Combining with the research status of plastic-state slurry permeability, this thesis has explored the experiment testing methods of plastic-state slurry permeability, and developed a corresponding special test device. Basing on the test principle of soil-porosity, the experiment testing methods of plastic-state slurry porosity has been formed combining with the similarities and differences during the plastic-state slurry and soil. It is provide according to confirm the gas migration risk time under the actual condition that deducing the quantitative relation model between the volume shrinkage of plastic-state slurry before initial set and pore pressure. This thesis established the gas migration physical mathematical model and the new method to evaluating anti-gas channeling ability based on the displacement process.The paper compiled the anti-gas migration evaluation software with the experimental data processing, model and evaluation method, enhancing the operability and practicability of the evaluation method. Based on the experimental method research, theoretical research and software programming, the results formed as follows:(1) The performances of static gel strength, plastic-state slurry permeability, porosity and plastic-state volume shrinkage, which is material physical and chemical properties of cement slurry, were put forward as the key performance indicators for preventing the early gas channeling based on analyzing the slurry’s hydration mechanism.(2) Basing on the study of plastic-state slurry permeability, the test method of plastic-state slurry permeability was formed and a corresponding special test device was developed. Study thought that plastic-state slurry permeability declining over time and tending to become stable gradually after condensing into cement stone.(3) The test method of plastic-state slurry porosity has been formed in this paper combining with the particularity of cement hydration and the testing principle of soil porosity. Study thought that plastic-state slurry porosity declining over time and tending to become stable gradually after condensing into cement stone.(4) This thesis deduced the relation model between plastic-state slurry volume shrinkage and pore pressure based on establishing the physical model of "casing-slurry-formation". Study thought that gas migration risk time is from pressure balance to initial set combining with testing the gas channeling start-up pressure of mud cake.(5) The new method to evaluating anti-gas channeling ability bas been established and the anti-gas migration evaluation software has been compiled based on researching on the gas migration physical mathematical model. This new method can evaluate the anti-gas channeling ability of cement slurry effectively considering the actual working state parameters oil and gas well of and the performances of plastic-state slurry.