Because of the fact of increasing complexity of well paths (higher deviations, longer horizontal sections), the demand of reasonably priced casingconnections with high capability of torque transmission is rising. On the one hand it would be useful to have the option to turn the casing-string during running in hole, in case it could not be lowered by its own weight, on the other hand the quality of the cement bond should be improved with rotating during cementing. The on the market available flush type connections, are normally high priced and have additional technical disadvantages like difficult handling and low connection efficiency and therefore seem not to be the right choice for marginal field exploration.

The paper shows the connection development and first practical use of a casing-string of the size 4½-in. 13.5 lb/ft of the grade L-80-1, with a torque capacity of 11,000 Nm and additional significant overtorque capacity. The connection efficiency is 100% and the connection is still compatible to standard API Buttress accessories like reamer shoe or landing collar.

Described is the development from the prototype to the serial connection type and its first field trial. Explained are the differences to the API Buttress thread and the performance tests this connection was subjected too. Torque-turn diagrams recorded during make-ups, which were carried out in the mill and in the field, are presented and discussed. Special attention is given to proper connect to API Buttress connections (reamer shoe, liner hanger packer, landing collar).

In the end an outlook about future possible applications and benefits for the oil industry is given. The connection fulfills the features: High robustness, reasonable cost-performance ratio and API Buttress compatibility and can also be used for casing drilling whereas special enhanced tightness due to gas was not a development goal.

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