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Kelasu gas field in Tarim Basin is characterized by ultra-deep (6500-8000m), ultra-high temperature (160-19°C) and ultra-high reservoir pressure (110-136MPa). The wellhead pressure during production is also as high as 80-100MPa. Rigless well intervention is always difficult to perform because of the high well control risks. Slickline testing, electric line testing and optical fiber monitoring have all been tried, but problems like breaking of slickline, loss of signal, falling of instruments into well, etc. were encountered. A slickline fishing technology has been used for bottom hole well surveillance in this area with many optimizations on the instruments. Grease injection sealing assisted by packing sealing is used to reduce friction of slickline and to guarantee well safety during operation; a choke tube stabilization device is invented to deal with the eccentric wearing of slickline and choke tube; self-supporting lever together with 8 anchor ropes are used to stabilize the blowout prevention tube assembly to withstand the high wind in the mountainous area; grease collection device is used to avoid the discharge of grease into the environment. The technology has been successfully used in more than 70 wells in Kelasu gas field. The interventions include production testing, pressure built up (PBU) testing and well interference test. The maximum setting depth of the manometer reaches 7189 m. The highest wellhead pressure during testing reaches 90 MPa. Longest pressure survey time comes up to 52 days. No surface or downhole problems have been encountered and all the required data have been acquired. The wells were not killed during the intervention so the reservoir is well protected. Well interference tests were conducted in Keshen 8 block using this technology. The results showed very good interwell connectivity and suggested that well spacing should be enlarged. The development program of this block was adjusted accordingly and it turned out that the expected production rate was achieved with 4 less wells. Besides, the drilling thickness of the target formation was reduced from 200m to 130m and the same well productivity was also obtained. Now the slickline fishing bottom hole pressure survey technology has been extensively used in the ultra-deep HTHP wells in Kuqa Foreland Area. It has been field proven for simple operating, less cost and formation protection. It can be used anytime in the life cycle of a well to evaluate the reservoir dynamic data, to deploy new wells and to optimize the production system of existing wells. |
