Salem G. Aljuhani¹

(1) Saudi Aramco, Dhahran, Saudi Arabia

ABSTRACT: Data Integration for Unayzah Reservoir Characterization: Saudi Arabia

A set of well logs and 3-D seismic data from a new oil field in Saudi Arabia was utilized to characterize Unayzah reservoir and to evaluate the detectability of fluid-anomaly signal. Unayzah reservoir consists of two sandstone compartments that are thoroughly separated by a siltstone layer and sealed by the base Khuff shale. Production is controlled by a combination of structural and stratigraphic trapping.

I studied in detail the nature and degree of the correspondence between the seismic data and the wireline log data in this field. The gamma-ray logs provide a high-contrast sharp definition of the Unayzah units, and they provide valuable information on the reservoir quality. The impedance logs and synthetic seismograms provide some relevant information on the reservoir quality. The seismic amplitude is locally deteriorated by strong amplitude interference from the overlying Khuff Formation, but it can provide fair description of the reservoir properties. The seismic time picks can be used for structural mapping purposes along with known depth control.

A plane fit of the estimated oil-water-contact (OWC) seismic times produced a tilted OWC time map that indicates a simple velocity gradient. This procedure of estimating the OWC does not require information on velocity nor seismic reference datum. It provides an improved picture of the relationship between the lithologic units and OWC. The OWC time at the well locations was estimated within ±2.5 ms (±17 ft depth error). This adequately accounts for lateral velocity variations and datum plane adjustment for improved time to depth conversion.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado