Application of Different Seismic Reservoir Characterization Methods to Real Cases: a Powerful Combination.

Summary

The present studies quantify the benefits of integrating, by means of statistical and geostatistical methods, 3D seismic attributes and well data to predict reservoir properties and reduce volume uncertainties. A clear complementarity exists between well data (which are few, biased in location but accurate) and 3D seismic data (which are dense, regularly sampled but noisy and ambiguously related to reservoir parameters). The basic principle of seismically supported reservoir characterization is to find seismic attributes which show good correlation with the desired geological parameters (porosity, net sand, HPM, presence of gas,…).

Using 3D seismic attributes, to guide the mapping of well data values, may bring substantial reductions (up to 50 % in the shown case) bf predictions errors. Geostatistical methods allow the evaluation of uncertainties associated to predictions by means of conditional simulations which reproduce the variability measured in the data.

Associating uncertainties to the prediction is the key element for the credibility a reservoir characterization methodology.

In complement to the above approach, Total has developed a statistical method of cluster analysis for the automatic research of discriminant seismic attributes. Theoretically, the number of involved seismic attributes is not limited. The prediction is not linear. As the approach is more global, only few wells may be used.

The combined use of this approach and geostatistics leads to a further reduction of uncertainties: the optimum attributes found with our approach are then injected in a geostatistical software.

Statistical and geostatistical methods provide the mathematical framework to quantify uncertainties, leading to a better assessment of the Exploration and Development risks. This data integration has great cost savings potential. in particular in the delineation phase of a field, and will play an important role in certification exercises.

Introduction

In a world of severe economic constraints on projects, it has become essential for Oil Companies to obtain, as early as possible, an accurate assessment of the reservoirs characteristics and the hydrocarbon volume available in the subsurface. Towards that goal, 3D seismic and Geostatistics are playing paramount roles (Ref. 1).

3D Seismic & Geostatistics

3D seismic has been successfully used for over a decade to define reservoir boundaries and the geometry of sedimentary bodies. But it is only recently, due to the progress of seismic processing (amplitude preservation. zero-phasing…) that the quantitative utilisation of seismic attribute was made possible.

By their nature, seismic data are complementary of well information. Wells are typically scarce over a field. They have been spudded, at least at the exploration stage, with the specific objective of finding hydrocarbons. They are therefore likely to provide a biased image of the reservoir. The wells informations are rather accurate but only representative of a limited zone around the wells bores.

On the other hand, 3D seismic data are dense and equally sampling the subsurface.

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