A new type of the 8000m drilling rig ZJ80/5850 has been researched, manufactured and successfully applied for ultra-deep well drilling in the submountain region of China's Tarim oilfield. The new kind of rig was developed to deal with the problems of load incapacity of drilling with the 7000m rig and high cost of drilling with the 9000m rig in ultra-deep well drilling.

Deep or ultra-deep well drilling operations in the piedmont area were predominated by the 7000m rigs. In order to tackle the situation of ultra-deep well drilling in the piedmont zone in Tarim oilfield, primary technical parameters of the rig had been enhanced with maximum hook load capacity 5,850kN, 52MPa high pressure rig pumps were equipped, compacted strands high tension wirelines were first used, derrick structure of the rig was optimized, and high strength material was selected for the main structure. Thereby a perfect general technical scenario of rig and associated techniques were formed.

The Tarim basin in northwestern China featured complex geological conditions and deep buried reservoirs. The potential risk of the 7000m rig safety as drilling around 8,000m ultra-deep wells emerged and the rig accident occurred as the big-size casing was deeply set due to the bare weight of the casing exceeding the load capacity of 4,500kN. Drilling efficiency has significantly been enhanced after 22 rigs of the type 8000m rig were applied for ultra-deep well drilling in the Tarim oilfield in less than three years. The 8000m rig has become prevailing equipment for drilling operations in the submountain region of Tarim. The procurement cost of roughly USD2.5bln was cut down per set of the 8000m rig as compared to that of the 9000m rig. The daily drilling rate per rig was saved by 20%-30%. Total amount of USD36.8bln for integral cost of drilling was saved per rig per year.

The optimization of the 8000m rig parameters and advanced associated technologies have filled in the gaps of China's rig standards and perfected the standard series of China's rigs. R&D of the new type 8000m rig was a result of market demand and satisfied by clients for the exploration and production of ultra-deep buried reservoirs.

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