Willingness to revive production from a High Pressure-High Temperature (HP-HT) well, characterized by poor productivity performance, led to the project of drilling a reentry horizontal drain hole at 5, 500 m TVD. The initial well, drilled and completed in early 1993, hit the target in an area of unusually poor petrophysical characteristics, where the fractures of the dolomitic reservoir were found to be filled with sedimentary dikes.

As a consequence, the well productivity performance was remarkably lower than expected, and the well was soon shut-in.

The well, named Trecate 14, was drilled in the Trecate-Villafortuna field (the biggest and deepest onshore producing oil field in Europe, located in the north-west part of Italy) at 6, 241 m TVD. Wells in this field feature production rates of about 4, 000 bopd, with flowing well head pressures of 400 bar (5, 700 psi) and temperatures of 120°C. The original reservoir pressure is over 1, 000 bar (14, 500 psi) and temperature as high as 170°C–180°C.

Studies undertaken by Geologists and Reservoir Engineers show that an area with suitable petrophysical characteristics could exist nearby the actual bottom hole location, some 150–300 m away.

A technical and economical proposal to recover this multimillion well to profitable production was submitted and approved by Company's Management.

In order to ensure maximum success, as well as achieving a certain offset from the initial wellbore, a certain horizontal displacement was required to increase chances of crossing good producing fractures. Following the 7" casing window milled at 5, 489 m, the drain hole was drilled to 5734 m measured depth; 64 m were drilled horizontally. Drilling was stopped due to repeated heavy mud losses which, on the one hand almost prevented the drilling operations being continued in a safe manner, while on the other hand indicated that potentially good producing fractures were crossed.

The successful conclusion of this project demonstrated the feasibility of ultra-deep drain holes under limited conditions such as those mentioned.

Furthermore, it demonstrated that it is feasible to use currently available technology with only minor modifications, provided that suitable procedures and contingency plans are implemented in advance.

The well was completed introducing modifications in the standard completion design used for other wells in the field. At present, the well is the best field producer.

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