The B24 well in the Fidaa Field was the first dual-lateral, underbalanced
horizontal well drilled in Libya and the second well of Zueitina Oil Company’s
(ZOC) underbalanced drilling (UBD) campaign.
The targeted hard dolomite reservoir, "Facha," is partly depleted
after 23 years of production to a 7.2 lbm/gal equivalent mud weight. Nitrified
diesel, a two-phase drilling fluid, was used to drill the reservoir section of
the B24 well underbalanced to avoid circulation losses and formation damage.
Real-time logging while drilling (LWD) was crucial for geosteering the well
path in a complex reservoir structure, and real-time annular-pressure
measurement also was necessary to ensure that the underbalanced condition was
maintained throughout the entire UBD phase.
Two 6-in. horizontal drains were drilled successfully with 2,053- and
1,517-ft drain lengths. Integrated efforts of ZOC and service companies of
various disciplines during planning and operation stages of the well led to the
success of the project. No quality, health, safety, and environment (QHSE)
incidents were reported, and the productivity of the well was enhanced
The B24 well's production alone contributes more than 30% of the total Fidaa
The Fidaa field in the north of Muelah graben at the western edge of Sirt
basin was discovered in 1979. The structural map of the Facha reservoir (Fig.
1) shows the structure to be northwest/southeast trending with approximately a
9.5×2.5-km size and a pay zone thickness of 28 ft. A total of 23 vertical wells
were drilled to date in the Fidaa field. Well B24 was the last one drilled
horizontally with two lateral legs. It was completed in May 2005.
Facha reservoir "C" layer is dolomite with vuggy porosity of 23% on
average, and logs indicate extensive fracturing. The reservoir pressure of the
upper Facha ranges from 1,600 to 2,330 psi, and the average pressure along the
planned drainhole in the Facha C was 1,900 psi at 6,085 ft total vertical depth
(TVD) (6 lbm/gal equivalent mud weight). The Facha reservoir is an oil-bearing
pay zone with a stock-tank oil gravity of 41.7°API, a gas/oil ratio of 68
scf/STB, and water cut ranging from 6 to 70%.
Because of a partially depleted pressure of the Fidaa field, lost
circulation and other drilling problems were encountered in the field.
© 2009. Society of Petroleum Engineers
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- Original manuscript received:
24 January 2007
- Meeting paper published:
30 April 2007
- Revised manuscript received:
6 February 2008
- Manuscript approved:
8 February 2008
- Published online:
1 June 2009
- Version of record:
1 June 2009