Engineering incidents frequently happened at the top formation of natural gas exploration wells and development wells in south Los Tan blocks of Turkmenistan, one of the reasons is the difficulty of conditioning drilling fluid technology. By laboratory studies & evaluations and field applications, strong inhibitory polymer and polysulfide drilling fluid used at Well's section I and section II to overcome the problems, which are included poor diagnostic grade, clay stone, unconsolidated cements for sand and clay stone, high clay content (more than 50%), serious mud-making, bit balling, sloughing and shrinking of hole, etc completely meet the need to drill big hole(26" and 17-1/2") in long open hole, as well as to deal with the downhole complexities for a long time(the longest up to 4 months) in TD 3700m wells, and they ensured the downhole's safety, made the logging and running 13-3/8"casing in long open hole with one time successful.How to achieve the performance were discussed as conclusion, for instance, polymer glue for earlier stage, polysulfide for later stage, removing useless solids effectively while highlighting inhibition, reducing dispersing agent as low as possible, keep good rheological property and carrying cutting capability, etc. These are important to process the drilling fluid, and build a a technological package of drilling fluid for the top claystone formation of natural gas well with big holes and long open hole, in south Los Tan blocks of Turkmenistan. This drilling fluid system improved the exploration &development technology in South Los Tan blocks of Turkmenistan, which well guide and offer support to explore big hole and long open hole in clay stone formation.

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