Study On Leakage And Leakage Technology Of Cementing In Kuqa Mountain

Lost circulation, a complex situation which often happens during drilling,can not only extend the drilling cycle but also lose vast resources and cause the reservoir-damaging. And it may induce serious accidents like well collapse or blowouts once lost circulation cannot be properly controlled. Cementing operation cannot proceed normally once circulation loss happens during casing running, it would affect cementing quality seriously and burys hidden troubles for after exploitation. The situation of lost circulation is very serious in the Kuqa-piedmont-region of Tarim Oilfield.Lost circulation in running casing mainly occurred in the processes of casing running down and after casing was moved to the bottom to open pump to circulate. The thesis analysis that the reasons of loss circulation from the Kuqa-piedmont-region geological conditions, the commonly used well structure, common drilling fluid performance and process of cement casing running. Currently the design method of the speed of casing running and cyclic displacement (Including the decentralization process and circulating after casing was moved to the bottom) in Kuqa-piedmont-region based on the conditions of same returned speed, and ignore the influence of formation pressure ability, drilling fluid properties and the annular clearance. But, as the change of drilling fluid properties and the annular clearance may cause the differences between the design results and the actual situation of underground.Precise formation pressure values are the basis of leakage-proof design, and the formation pressure prediction model currently used in the kuqa-Piedmont-region does not apply. The most accurate method is formation pressure testing, as to those wells cannot do with the formation pressure testing, friction judgment method would be available. Drilling fluid rheological properties can influence its surge pressure in the flowing process, it has carried on experimental study on plastic viscosity change with temperature regulation and set up a prediction model. Irregular caliper caused by inadequate wiper trip can also lead to additional surge pressure in the casing running process. Based on the analysis of the lost circulation affecting factors, casing running speed and cyclic displacement calculation model has been set up by the principle of balancing surge pressure and formation pressure, formation pressure capacity, the change of the annular clearance and the rheological properties of drilling fluid have been considered in this model, and it also considered the plastic viscosity as a variable instead of a ration, which makes the result more accurate.According to the research, the results of thesis spot application was carried out in Kuqa-piedmont-region of Tarim oilfield. The whole construction process went smoothly, circulation loss was avoided successfully in the process of casing. And the critical cyclic displacement was predicted accurately, which has confirmed that the technology has a useful field guiding significance. Research results has provided a technical countermeasures for solving the serious problem of loss circulation during casing running.