Planning And Drilling A World-Record Water Depth Horizontal Drain
Authors: Girola Giorgio , Newton Grahame , Ciprigno Maurizio 
Published: October 2008

DESCRIPTION

Horizontal drilling technology has been extended significantly by a recent breakthrough in an offshore short radius project in Italy. This paper will discuss the tools, technology and operational aspects of drilling an unconventional large-diameter short radius drain hole in competent formation and in an extremely deep water environment. Several world records were established and horizontal drilling technology milestones were achieved during the drilling of a drain hole by AGIP in the southern Adriatic Sea between Italy and Albania. Aquila 2, the name of this well, is the first short radius drain hole drilled from a semi-submersible rig. The well was drilled in 830m water depth, which is a world record for any kind of horizontal well. The drain was built to horizontal at 3953m TVD and achieved a horizontal displacement of 200m drilled in fractured limestone. A newly designed 6-1/2" OD, field adjustable, short radius drilling system, incorporating a near bit inclination sensor and a short radius MWD tool was used in the project and achieved a radius of curvature of 30m in 8-3/8" borehole.

Besides these technological achievements this project involved reservoir characterization, evaluation of the formation petrophysical properties and production performances from the appraisal well. Taken together, these efforts make the project a uniquely, multi-disciplined endeavor.

Encouraging production rates were achieved during an 85-day, Long Production Test (LPT) which will be used in planning and implementation of future activity in the basin.

INTRODUCTION

The Aquila field/structure is located in the southern Adriatic Sea between Italy and Albania, approximately 45 km east of the Italian city of Brindisi, in 830m water depth. Hydrocarbon potential in the area was appraised since the late seventies. In particular, exploration wells showed the importance of the Scaglia Limestone as a reservoir.

Data from the reference wells indicated that the most suitable zone for further investigation was the top 50m of the fractured Scaglia Limestone. However, due to substantially higher pore pressures above, and the fractured nature of the zone of interest, it was necessary to plan any future activity with a 9-5/8" casing shoe set at the very top of the Scaglia. Drilling without severe losses cuuld then proceed in 8-1/2" or 8-3/8" hole size.

Data from reservoir engineering studies indicated that a 150m to 200m horizontal drain drilled perpendicular to the fracture system would be necessary for a meaningful long production test (LPT). To enable intersection of the top 50m of the Scaglia with an 8-1/2" or 8-3/6" horizontal drain, it became necessary to design a short radius drilling system that would allow kick-off below the 9-5/8" casing shoe and build angle so that no more than 35m of True Vertical Depth (TVD) was consumed prior to achieving 90 degrees of hole inclination.

A 6-1/2" OD, field adjustable, short radius drilling system along with the associated measuring instrumentation (MWD) was designed and tested prior to being applied in the Aquila 2 wellbore.

Aquila 2 was subsequently planned and drilled utilizing the semi-submersible drilling rig, Reading & Bates "Jack Bates".