Abstract
Discovered in 1949 with a rate of (195,000) bbl/day from pay zones in Mishrif and Zubair Formation, the expected production of Zubair field is anticipated to be 1125 million bbl/day. Despite this production history, there is a major deficiency in detailed petrophysical analysis of the producing zones. In the present study well log data of 7 wells, selected from numerous wells, are investigated in details to examine the reservoir properties and characterize the reservoir architecture. The petrophysical analysis of Mishrif Formation indicated two or three pay zones. Lithologically, all zones of Mishrif Formation are dominantly clean limestone to dolomitic limestone with zone 2 and 3 reporting higher dolomitic content (20% to 40%) compared to zone 1 (6% to 13%). Mishrif pay zones indicated a relatively good porosity (18% - 24%) with zone 2 predominant in secondary porosity associating dolomitization processes. In Zubair Formation one pay zone is identified but locally could separate into two zones. The clay content is generally low with average content between 2% and 3% while the average porosity showed slightly better values in zone 1 (~0.20) compared to average porosity of zone 2 (0.17) that is rich in silt content associating deposition at a relatively deeper parts of the shelf. The average water saturation shows distinct lower values that vary between 15% and 18.7%. The petrophysical results are statistically analyzed and property histograms and crossplots are constructed to investigate mutual relationships. Such analysis is essential for understanding the reservoir architecture and calculations of reservoir capacity for future development.
Highlights
Log data from seven wells producing from Mishrif Formation (Zb216, Zb225, Zb280, and Zb302) and Zubair Formation (Zb229, Zb278, and Zb309) (Figure 1) are numerically processed and verified consistent for petrophysical analysis
For each pay zone or reservoir interval in any well, the statistical analysis provides a set of outputs including tabulated values, histograms, and cross plot for each property involved in reservoir characterization
Zubair field produces oil from two packages; Mishrif Formation normally encountered at the depth of 2200 - 2600 m and Zubair Formation located at the depth of 3000 - 3600 m below land surface
Summary
This requires the conjugated efforts of geoscientists and engineers in a multi-disciplinary synergistic approach to recognize the complex variations in reservoir heterogeneity and its associating hydraulic properties [1]. Such synergistic approach is discussed by Harris et al in [2] and emphasized the importance of geological and engineering approaches for reservoir characterization. Worthington and Cosentino in [4] presented the effect of cutoffs value on integrated reservoir studies and highlighted the importance of petrophysical cutoffs on reservoir characterization for both static and dynamic models that inconsequence lead to realizations of the asset value
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