In the HP-HT field of Villafortuna Trecate, located in northern Italy, five horizontal drain holes have been drilled in the last few years. Existing wells have been sidetracked to access trapped reserves and to enhance production. Since the field is the deepest onshore European field, these wells are amongst the deepest horizontal wells ever drilled.

Final measured depths are over 6300 m with an average true Vertical Depth of about 6000 m.

Several technical problems related to the extremely severe HP-HT environment were met, both in drilling, completion and stimulation phase.

This paper briefly describes the Trecate 9 drain hole drilling and completion execution, with emphasis on the stimulation technique adopted to obtain an effective acid diversion along 250 meters of open hole section, the longest in the field.

Without getting into complicated analysis involving fluodynamics, kinetic of chemical reactions, effects of bridging and chemical diverting agents that would necessitate separate studies, the description of this technique is focused on basic design concepts and how operations have been carried out on this field application. Nevertheless we believe that this simple and cost effective technique represents a real opportunity in all the cases when diversion of treating fluids is a concern, and hope that in the future, more work done following this basic guideline will lead to many other successful field applications.

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