The crossing of a series of high, parallel, elongated and with steep scarp mountains in the Serrana Province, between Ca´ceres and Cuiaba´, Mato Grosso State, Brazil, constituted a great technical challenge for implementation of the Bolivia - Mato Grosso gas pipeline. Due to environmental preservation, the gas pipeline could not cross the crest of some of these mountains using conventional surface methods and the alternative of surrounding the mountains would have caused an extended additional path, with appreciable additional cost. The economically viable alternative was the horizontal directional drilling through the most critical mountains: Piraputanga Ridge with 850m, Cachoeirinha Ridge with 943m and Palmeiras Ridge with 867m. One of the difficulties was the drilling of the very compact and abrasive Alto Paraguay Group Proterozoic low metamorphic rocks intercalated with clastic sedimentary rocks. The horizontal directional hole intersects in high angles the strongly dipping layers of rocks. The layered sequences of sandstone capped by siltstones provide the aquifer condition to Raizama Fm. with strong water flow. To prevent any environmental damage, the conventional hole design was modified, which allowed the drilling with water, instead of bentonitic drilling fluid. The horizontal directional drilling consisted of a pilot hole with 10.14 inches diameter, drilled with down hole motor and an electromagnetic steering system. The first enlargement of the pilot hole went to 22” diameter and the last one to 30” using special reamer tools. The pipes of the Bolivia - Mato Grosso gas pipeline have 18” diameter, with a special line coating to prevent damages during pulling in contact with rocks. No problems occurred during the pulling operation of the pipes along the holes. The proposed three horizontal directional holes were very successful and the projected designs of the well were fully achieved, with a very small offset in the forecasted exit points. After long weeks of hole opening and preparatory works, all three pulling operations of the pipestrings along the holes went very smoothly.

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