This paper presents a case history on drilling of an ultra-deep exploratory well with a lot of problems and final solution in a complicated K structure in Uzbekistan. Drilling troubles include serious stuckpipe resulted from drilling-in the unexpected high pressure brine formation, malfunction of the high density drilling fluid system, and subsequent failure of the fishing jobs, unsuccessful sidetracking, bad job of cementing, etc.

After the drilling fluid system was improved, the high pressure layers were isolated, and the proper drilling measures were carried out, the second sidetracking gained success and the well was completed. Afterwards, an adjacent ultra-deep well in the same structure was smoothly drilled and completed by means of optimization of the casing programs, drilling fluid system and technical measures.

Drilling practices of previous offset well indicated that the formation is pay zone and produced oil, while the same formation at the same depth in the well JD3# produces brine water, which resulted in overflow during twice sidetracking of the same formation. The high and low pressure layers existed in the same section after drilling-in brine formation would produce complex against drilling and subsequent operations, therefore a 7-inch liner was set to isolate the high pressure formation, so as to create a good condition for deeper drilling operation. High-density drilling fluid with good precipitation stability and lubricant anti-sloughing properties also contributed to the success in drilling of high pressure brine layer and salt gypsum formation.

Accurate determination of the must-be-blocked point is the key to the success. Drilling of the well with problems and its final solution could be used for a technical reference as drilling in deep or ultra-deep wells in similar geologically complicated oil and gas fields.

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