Seismic Characterization of Reservoir Architecture and Facies Distribution in a Carbonate Platform Setting: Dynamic Implications for Production in a Super-giant Middle East Field
Authors: Yin Y. , Lawrence D. A. , Vahrenkamp V. , Kourbaj A. , Helmy H. , Gashut M. , Al-Mehairi Y. 
Published: February 2011

The studied Super-giant Middle East field is producing from the Shuaiba carbonate reservoir of Early Cretaceous (Aptian) age, spanning various depositional environments including platform, margin and clinoforms. The field has been producing for over 40 years and has been under peripheral water injection for more than 30 years. A 3D seismic survey was acquired in the late 1990’s. The overall platform architecture and clinoforms are well imaged by seismic data and were incorporated into the geomodel building; however subtle seismic features and discontinuous intra-reservoir reflectors were not interpreted and not incorporated in the geomodel. With continued field production and injection, several development challenges are apparent including differential sweep in the platform, water fingering along the platform interior / margin boundary, and poor pressure support in the clinoforms. The current reservoir model shows limitations in correctly history matching and predicting field performance. A new geological model with more realistic description of reservoir heterogeneity is needed to improve the future field development strategy. A detailed seismic interpretation was therefore undertaken to extract more geological information from the previously un-interpreted subtle seismic events. This paper presents the results of seismic reinterpretation in the platform interior and margin areas.

The relatively subtle seismic events are complicated by rapid vertical and lateral facies changes, small impedance contrasts and thin layers. Although more challenging to interpret, they contain important information for facies distribution and more detailed strata geometry. Time lapse cased hole saturation logs show water breakthrough along certain intra reservoir surfaces or related to particular facies. These seismic features, once interpreted, should improve the understanding of injected water movement.

Well information was maximized to decrease the interpretation uncertainty. Seismic-well calibration was performed to understand seismic response to different facies and facies associations. Some subtle seismic events are related to significant reservoir facies: the thin coral facies associations, although not resolvable, are detected by subtle amplitude changes. Internal reservoir surfaces show varying seismic character depending on interference from above and below. Resolution is a key issue due to the presence of thin layers. Stochastic seismic inversion was performed to improve resolution. With guidance from seismic-well calibration and the increased resolution from stochastic inversion, the following results have been achieved: Additional intra-reservoir surfaces in the platform area have been interpretedThe distribution of coral-rich facies associations has been mapped3D geo-bodies of the dense ponds and channels have been extractedA new interpretation of the third order MFS (Apt 3) bounding the platform margin has been proposed

The above interpretation results combined with core, log, reservoir monitoring and production data, have given a better understanding of injected water movement. Injection, production, completion and drilling strategies are being adjusted accordingly to smooth the water front advance. Reservoir architecture and facies distribution were refined for incorporation into the new static model building, which will ensure a more realistic dynamic simulation and assist the field optimization strategy.