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.