Challenges of Reservoir
Characterization
in
Mauddud
Carbonates
: North Kuwait
By
Hussain Al Ajmi1
(1) Kuwait Oil Company, Kuwait City, Kuwait
The Mauddud Formation in North Kuwait consists of Early Aptian carbonates
deposited in a low angle ramp setting. The
reservoir
holds more than 6 billion
barrels of in inplace oil in two adjacent doubly plunging anticlines of
Raudhatain and Sabiriya structures. Initial
reservoir
characterization
of the
field was based on primary depositional characteristics. Static data from a
relatively dense well controls but limited dynamic data were available and made
use of. Availability of more dynamic data necessitated a modified
reservoir
characterization
to account for the fluid flow.
Mauddud formation is under production for last 40 years from 18 wells in
Raudhatain field. Only two wells have cumulative production over 20 million
barrels each while the rest wells have produced less than 1 million barrels.
There is very little aquifer support and the reservoir
pressure had dropped by
1400 psi for a cumulative production of 4% of initial oil in place. An inverted
5 spot water injection pilot was designed and implemented in an unfaulted area
of the field to guide pattern injection for the
reservoir
. Water break through
was observed in the producers within a time range of 2 to 14 months.
Analysis of static and dynamic data from the pilot study broadly associated
primary depositional rock fabric as being the main control over fluid movement.
Rudistic floatstones, deposited in inner-ramp/restricted lagoonal settings was
found to be acting as thief zones. Core recovery across such facies is very
poor. Zones with such lithofacies were identified from cores and electrologs.
The reservoir
was developed with inverted nine spot with 59 producers and 23
injectors. Zones having Rudistic floatstone facies were not perforated in the
injectors.