Wells in kuqa foreland area of Tarim Basin are mostly ultra-deep and HTHP wells. The well depths vary from 6000 m to 8000 m. The reservoir temperature and pressure are between 135-180℃, 100-135MPa respectively. Coiled tubing was introduced to conduct the down-hole operations in this field. Through improvements of many technologies, six operations were successfully conducted and operating time was saved by more than 50%.
CT operations in HTHP wells were made available by carefully evaluating and selecting the proper CT assembly and operating parameters. A standardized modeling workflow was established, including force analysis, hydraulic analysis and fatigue analysis, to systematically evaluate the operation, and then optimize the CT assembly, the wellhead equipment, the operating parameters, etc. A real-time CT detector was also developed to monitor the properties of CT while operating. Besides, a series of on-site operation criteria were established to control the process of CT operations.
With these modeling, optimizing and monitoring technologies, CT operations were firstly tried in ultra-deep wells in the basin area of Tarim Basin, whose well depths are more than 6000m but with normal pressure and temperature systems. Drilling and milling, acidizing, jet perforating, and staged proppant fracturing were all realized in these wells. Well YM704, with down-hole pressure of 82MPa and down-hole temperature of 148℃, was acid pickled with CT at vertical depth of 7287m. Afterwards these technologies were introduced to kuqa foreland area, where the wells are mostly HTHP gas wells. Six down-hole operations have been tried and only minor troubles occurred. Well KS2-2-12, whose down-hole pressure is 102MPa and down-hole temperature is 160℃, was sand flushed by CT at the depth of 6182m, and a 46m sand plug in the wellbore was cleaned out. Well DB101-1, with down-hole pressure of 92MPa and down-hole temperature of 130℃, was conducted workover by CT. CT was run to 5373m and successfully drilled and milled the bridge plug. By using CT operations in these wells, more than 50% of the operation time was saved.
CT has been proved to be an efficient tool for down-hole operations. It can reduce the cost of operations significantly. However, the use of it was restricted to conventional wells. This paper introduces trials of CT operations in ultra-deep and HTHP wells, providing a reference for CT operation design in tough conditions. Resistance of running in hole was also encountered occasionally, but it is hopefully to be avoided by optimizing run-in modeling.
