Wintershall Dea, one of Norway’s largest oil and gas producers, turned to Cegal to improve their understanding of the subsurface geology in the Nova field. 

Applying an innovative approach to seismic inversion, Wintershall Dea was able to build a robust and comprehensive model of the subsurface and produce high-quality reservoir property estimates with associated uncertainties.

A Need for Better Subsurface Predictions

Wintershall Dea, a long-standing customer of Cegal and operator of the Nova field, aims to maximize production with an effective development strategy. To do this, a clear understanding of subsurface geology – in particular, sand body connectivity and relationship to other boundaries – was required. 

To gain a better understanding of the subsurface, Wintershall Dea, looked to build upon previous studies with a new approach. As a provider of modern Reservoir Characterization and Inversion Software, Wintershall Dea turned to Cegal for help.

Applying QI Techniques

We began our work by applying particular Quantitative Interpretation (QI) techniques on Wintershall’s seismic data. First, we performed a Colored Inversion to improve the resolution of the seismic data and convert it to relative band-limited impedance. This helped us make the visual comparison with geology more accessible.

Then, we used the Extended Elastic Impedance (EEI) seismic projection method to discriminate between sand and shale and water and oil. This helped Wintershall connect the seismic inversion results with porosity, fluid content, and lithology. This further enhanced the visual representation of the various reservoir properties.

Colored Inversion and EEI provided Wintershall with a better understanding of the subsurface geology and an improved interpretation of certain surfaces. The process could have ended here, but to improve the accuracy of our predictions in even more detail, we turned to a more advanced seismic inversion method: One Dimensional Stochastic Inversion (ODiSI).

Using One Dimensional Stochastic Inversion (ODiSI) for Improved Insights

Initially developed by BP and later commercialized by Cegal, ODiSI is a novel approach to seismic inversion. ODiSI uses all known information about the target field and enables the user to create thousands of realizations of seismic trace locations within a Bayesian framework, one trace at a time and independent of the previous trace. These realizations are known as pseudo-wells, which are based upon lithology columns created from bed thickness statistics, a geological model, and individual facies-based rock physics models.

The primary output from ODiSI is probability curves for each facies, from which we could derive specific reservoir properties. Using ODiSI on the Nova field, we were able to generate several output volumes successfully, including net-to-gross cubes, lithofacies, and various percentiles.

Deeper Insights and Reduced Risks with ODiSI

Developing an oil or gas field is always associated with risks and uncertainties. With the help of Cegal and ODiSI, Wintershall has considerably reduced these risks and gained new and improved insight into the subsurface geology of the Nova field. 

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