B.  Al-Qayim*+ and F.  Rashid*

* Department of Geology, College of Science, Sulaimani University, Kurdistan, Iraq.

+ corresponding author,

The Albian Upper Qamchuqa Formation in NE Iraq is part of an extensive dolomitized carbonate platform developed during the BarremianAlbian over the passive continental margin of NE Arabia. Recent drilling at the Taq Taq oilfield in Kurdistan has renewed interest in this formation as a reservoir unit. In this paper, the reservoir and petrophysical characteristics of the Upper Qamchuqa Formation at Taq Taq are described using data from wireline logs, cores and thin-sections from four wells.

At Taq Taq oilfield, the Qamchuqa Formation can be divided on the basis of lithology into two units: an upper Dolomite Unit and a lower Limestone Unit. The Dolomite Unit is 140-190 m thick and is dominated by massive dolomites and dolomitic limestones. High porosity values (up to 26%, estimated from well logs) were recorded in intervals comprising fine to medium crystalline planar-e to planar-s type dolomite which were frequently oil stained. Pore types include microvugs, moulds, fractures, stylolites and intercrystalline porosity. The Limestone Unit is 72-55 m thick and is composed mainly of bioturbated bioclastic limestones with minor dolomites. A wide range of carbonate facies are present and are dominated by foraminiferal wacke-packstones and rudist packstones.

Wireline log data was used to characterize the reservoir quality of the Qamchuqa Formation at Taq Taq. Four porosity units were recognized. The upper porosity units has the best reservoir quality with average porosities of 15 %, compared to the second unit (7.5%), the third unit (7%) and the fourth unit (4%).

Different cut-off values were estimated, and related petrophysical parameters were evaluated and were used to subdivide the reservoir succession into three reservoir units. The uppermost of these units was found to have the best reservoir characteristics and represents the upper part of the Dolomite Unit. It has a thickness of 31-43.5 m with 25-41 m of net pay and  82% oil saturation. Flow in this unit is dual, dominated by fracture flow superimposed on matrix flow.

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