Print this pageAAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Using Spectroscopy Logs to Enhance Formation Evaluation and to Guide High-Resolution Facies Determination in the Nile Delta, Egypt
(1) Schlumberger, Cairo, Egypt.
(2) RWE, Cairo, Egypt.
A wide variation in rock quality exists in the sands and shaly sands of the Nile Delta. The mineralogy is complex, including the presence of feldspars, calcite, heavy minerals, and several different clay types. To improve evaluation of these gas-bearing reservoirs, neutron capture spectroscopy data is routinely acquired. The spectroscopy tool measures elemental concentrations, which are then converted into mineral concentrations.
Comparison of core mineralogical data with log spectroscopy data showed that the clay content from the standard clay matched the core data in the clean sand zones. However, in the more shaly parts of the reservoir, clay content from the spectroscopy model was overestimated.
Because of the relatively complex mineralogy, a linear calibration of minerals log data to core data was found not to be appropriate. It was, however, found that the clay volume could be more accurately computed from a multimineral solver using the elemental spectroscopy logs (rather than the mineral volumes output from the spectroscopy model). The computation process is described. It was also found that the aluminum log from direct aluminum yield measurement leads to the best clay estimation, as opposed to using the aluminum log from the aluminum emulator algorithm.
Results of the clay volume computation were used to calibrate the NMR clay cutoffs.
The mineralogical evaluation was further combined with calibrated microresistivity image data to generate a high-resolution lithofacies column, generating an accurate stratigraphic interpretation. Moreover, cutoffs were applied to generate a high-resolution sand count, sorting the reservoir units from the poorest to the best quality sands.
Examples illustrate how the use of the spectroscopy data enhanced standard formation evaluation in these shaly sand reservoirs. The examples also demonstrate that combining mineralogical information with high-resolution images can improve the understanding of the distribution of the best reservoir quality in the well.