Accounting for Deep-Water Reservoir Heterogeneities Through 3D/4D Seismic-Guided Reservoir Model Petrophysical In-filling
Authors: Amoyedo Sunday , Buraimoh Muse , Atoyebi Haraya , Modiano Thierry , Atewologun Adetayo , Soudani Mohamed-Amine , Piquet Gregoire , Vacheyrout Alain , Nateganov Arthur 
Published: September 2015

Adequate representation of reservoir heterogeneities in deep-water turbiditic systems presents a significant challenge in reservoir model building. Reservoir models are often too homogeneous, thus, making history matching not only difficult but sometimes less predictive and unreliable for long term production planning. In this paper we present a methodology to adequately capture and preserve variability in reservoir quality seen on well logs and seismic-derived reservoir properties inferred from 3D and 4D seismic. We demonstrate this technique in a deep-water field, offshore Niger delta.

In the first segment of the paper, we show the use of time-lapse seismic (4D) to update seismic-derived facies proportion cubes. Such update ensures consistency between the predicted facies proportions and 4D results. We further present a workflow to combine well results and the updated seismic facies probabilities to produce a geologic facies proportion cube that preserves heterogeneities and respects all available data (well results, 3D/4D seismic). The methodology involves the use of weighting factors on 3D-propagated well data (reference cube) and the 4D-updated seismic facies proportion cubes (auxiliary cubes). We conclude the study with the use of seismic loop-back as a quality control tool to check the overall consistency of the static model petrophysical infilling with seismic-derived reservoir properties.

We observed that most of the 4D-updated grid cells in the reservoir model are within the channel levees and lobe fringes, where seismic characterization might be less reliable but sometimes contributes significantly to oil in place (and reserve) in the field. The result highlights a useful application of 4D seismic for facies characterization in addition to reservoir monitoring. Also, the integrated facies proportion cube (well facies & seismic facies) not only retains known heterogeneities, it is consistent with 4D seismic. In conclusion, the seismic loop-back procedure, which involves the use of a calibrated petro-elastic model to generate reservoir elastic properties from model properties, shows that in most reservoir units in the field an overall good match was achieved between the reservoir model infilling and well data/seismic-inferred properties. In the field example, we observe that while a good match exists between the model and inverted parameters, nonetheless, important discrepancies have been found in areas lying mostly in wet channel levees. Careful analysis of such areas provides some insights about ways of improving the initial reservoir model infilling.

The paper presents a unique technique to account for heterogeneities (in 3D sense) in reservoir models. It showcases a pathway to integrate and maintain consistency among well data, 3D and 4D seismic towards building a consistent, reliable and robust reservoir model.