Research And Application On Thixotropic Cement Slurry

Many blocks contain leakage zones in Dagang oilfield, which can cause lost circulation in cementing and affect cementing quality. The thixotropic cement slurry which is one of the technology used in cementing leakage zones has some distinctive advantages, such as good leak protection and sealing, good gas block and low cost.In view of the defect of present thixotropic cement slurry, this paper chooses gel which has more performance as thixotropic agent. Then the mechanism of thixotropic agent gelling and the compatibility between thixotropic agent and cement additive are studied. At last, a new type of thixotropic cement slurry is developed by putting thixotropic agent into slurry and evaluated.(1)The gelling time and gel strength of several types of gels in different salinity and pH is explored in laboratory. The result shows AM gel has more performance than three else gel and is suitable as thixotropic agent.(2)The mechanism of AM gel is explored by IR spectroscopy. The acrylamide which has conjugative structure get together to form long molecular by ammonium persulfate and N,N'-Methylenebisacrylamide. Then the N,N'-Methylenebisacrylamide randomly reacts with long molecular and generate three dimension and net shaped structure.(3)The result shows that the amount of dispersant affects AM gelling more than AM, MBA, SG and fluid control agent. The dispersant inhibits the AM gelling. The performance of AM gel can be improved by changing the way of incorporating additive and adding more SG.(4)The formula of slurry is determined by adjusting the thickening and thixotropic performance of slurry. The thixotropic cement slurry has good thixotropic performance. The weight loss rate is high and the leak protection ability is good. The API fluid loss is 21ml in 75℃. The stability of slurry is very good and the free fluid is 0.2%. The permeability of set cement is very low. The compressive strength increases quickly in 0~3 days and is about 16 MPa after 3~4 days. The time waiting on cement is proposed to prolong to 48 hours.(5)Three wells in Dagang oilfield are selected to cement with thixotropic cement slurry developed in this paper. The cementing quality is quantification.