Enhanced Productivity of Carbonate Reservoir by Cross-Dipole Shear-wave Logging in the Bakr/Amer Field, Gulf of Suez, Egypt
By
Taher El-ZefZaf1, Maher Omara1, Theodore Klimentos2
(1) General Petroleum Company (GPC), Cairo, Egypt (2) Schlumberger, Cairo, Egypt
Earth stress patterns give a general indication of the most likely fracture
orientation or maximum stress trend. Nonetheless, local variations and the
effects of localized structures
, such as large faults, can modify the stress
pattern, counteracting or adding to the regional stress. Thus, such a local
stress and fracture profile information can be very meaningful to many petroleum
exploration and development related aspects, such as, selecting perforation
intervals and strategy, planning hydraulic fracturing operations, optimum well
placement, wellbore stability, sand production, and hydrocarbon migration.
In this study, cross-dipole shear-wave anisotropy logs, acquired in several
wells of the Bakr/Amer field (Gulf of Suez), were used to enhance the
productivity of the Nullipore carbonate reservoir by determining
the orientation
and magnitude of the principal horizontal stresses and detecting major fractured
intervals. Currently, the Bakr/Amer field accounts for 55% of the General
Petroleum Company’s (GPC) daily oil production. Approximately, 40% of this
amount is solely produced from the uppermost reservoir known as the “Nullipore”.
The cross-dipole shear sonic data was processed to obtain oriented fast and slow
shear waves. This information was then used to determine the direction and
magnitude of the in-situ earth stresses, and the orientation of fractures. Zones
showing significant shear-wave anisotropy were detected as open fracture
systems, using the shear-wave anisotropy data in conjunction with the Stoneley-wave
chevron patterns and other available logs. These intervals were subsequently
perforated and produced significant amounts of hydrocarbons. Further application
of this technique in several wells of the Bakr/Amer field proved that the
Nullipore reservoir productivity is primarily controlled by the
flow
contribution from natural fractures. New highly deviated wells were completed
over the Nullipore on the basis of the newly acquired information and excellent
results were obtained. Moreover, older wells were restudied and recompleted on
the same basis and a large increase of production was attained.