--> --> Abstract: Challenging Innovative Approach for Testing and Development of Zubair/Ratawi Reservoirs of Sabiriyah, North Kuwait, by Ali N. Khan and Sajan Nair; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Challenging Innovative Approach for Testing and Development of Zubair/Ratawi Reservoirs of Sabiriyah, North Kuwait

Ali N. Khan1; Sajan Nair1

(1) Field Development group, North Kuwait, Kuwait Oil Company, Ahmadi, Kuwait.

The Ratawi and Zubair Formation of Cretaceous age belongs to the category of ‘Minor reservoirs’ in Sabiriyah field, North Kuwait and are explored / exploited to limited extend only. Ratawi Formation comprises of Ratawi Limestone section which is dominantly carbonates, overlain by Ratawi Shale section which is an interbedded sand-shale sequence. Overlying Zubair Formation on the other hand is predominantly clastic, with thicker sand-shale interbeds making up a gross thickness of about 1500 feet. The Ratawi Limestone is interpreted to have been deposited on a low gradient carbonate ramp and consists almost entirely of limestone with intermittent beds of calcareous claystone and minor localized thin, very fine grained, argillaceous dolostone layers. Sandstone is very rare. The Ratawi Shale that underlies the Zubair Formation and is marked by flooding event that represents transgression resulting in deposition of shale with intervening shore face sandstone. Sand bodies within Ratawi shale are oil bearing. Zubair Formation is dominantly composed of progradational shoreface sands with interbedded vertical and lateral transmissibility barrier/ baffles.

Paucity of static/dynamic data was the critical part of the study. There were fifteen penetrations over an area of 145 sq kilometer out of which only in five wells these reservoirs were tested. Available static data integrated with seismic and dynamic well data were analyzed critically and few wells primarily meant for shallower reservoirs were deepening down to Zubair/Ratawi. Upon successful completion of drilling these reservoirs were tested. The deepest zone in Ratawi Limestone was tested first time and produced oil of 19 API. Isolated this zone with Bridge plug and a pay in Ratawi Shale was perforated but on activation it was found that bridge plug was moved and both the zones were in communication. Production logging was carried out and zonal contribution was ascertained. In wells drilled subsequently zones from Zubair also produced oil.

Drilling results of few wells during the last few months along with Geological cross section and correlation of logs with seismic interpretation and core study has upgraded the understanding of the reservoir. These static data integrated with dynamic testing data resulted in firming up few sweet locales. Significant quantity of STOIIP and reserves estimated erstwhile have been validated /upgraded. An aggressive development plan with production scheme has been formulated.