The GIG Consortium is hosted by the Norwegian Computing Center.

The GIG Consortium will develop new understanding, new methods and software for obtaining reservoir properties from geophysical measurements such as seismic surveys. Important reservoir properties are zonation, lithology and fluid classes, and petrophysical properties such as porosity and saturations. Methods will be based on established geophysical understanding and empirical rock physics relationships. The connection between reservoir properties and geophysical measurements is non-unique so developed inversion methods will utilize probabilistic models to quantify uncertainty and risk. Developed methods can be used for hydrocarbon exploration and field development.

Invitation

The GIG Consortium is open to oil and gas companies. There is a yearly fee and an initial enrolment fee. New consortium sponsors get immediate access to the software PCube and PCube+ and other consortium results.

Sponsor benefits:

• Early access to research results and new methods
  • Reports (only available to sponsors)
  • Software prototypes
• Immediate access to PCube+ and PCube executable and source code
  • Immediate access to updates, maintenance and support
• Influence on priorities
  • Direct influence on the Working Plan by voting for your favorite research and development tasks
  • Access to bi-weekly meetings with presentations and discussions

Better Geophysical Inversion

Geophysical inversion is a non-unique ill-posed inversion problem; many geometric configurations of geological properties can give identical measurement response and the resolution of the measurements makes it impossible to observe all relevant details. Unguided inversion is therefore impossible and some kind of regularization must be used. A cornerstone in all inversion techniques that will be investigated by the GIG Consortium is that the regularization is determined by geological constraints: gas is on top of oil, oil is on top of brine, the stratigraphy follows certain rules, et cetera. This will dramatically limit the search for the correct inversion result and give higher accuracy. The PCube+ software demonstrates this very clearly.

Traditional geophysical inversion focuses on the parameters that can be measured. For seismic inversion these are the elastic parmeters (V_p, V_s, ρ) and for EM inversion this is resistivity. Relevant geological properties such as lithofacies and fluid fractions are related to these parameters by rock physics relationships. The standard seismic inversion approach is to focus on elastic parameters and occasionally relate the background model to geological properties. Since geological properties are the main interest, the inverted elastic parameters are often transformed into geological properties using, again, rock physics relationships. We believe this can be done simpler and better. By focusing on geological parameters we can propagate the geological constraints consistently from the prior model to the final inversion result. This is illustrated here:

The scheme on the left is the traditional approach whereas the GIG Consortium will follow the Integrated inversion scheme to the right. Rock physics relationships are an important part of the Integrated inversion scheme but they are not separated from the seismic inversion process, the geological properties and the elastic parameters always exist side-by-side. The Integrated inversion scheme bypasses the stepwise approach and this has many advantages:

• It is simpler
• It is more accurate
• It propagates the uncertainty and ambiguity in each step
• Uncertainty in the rock physics relationships is handled properly
• Geological constraints are honored all the way and not forgotten in the intermediate steps
• It focuses on the end product, the geological properties relevant for exploration and production of hydrocarbons
• Geophysical parameters such as V_p, V_s and ρ are by-products and can easily be generated for QC

We have great expectations for this approach and have already proven that it works for elastic inversion. In the future we plan to improve the technology, expand it to new survey types, document its advantages and limitations, and make userfriendly versatile tools for the GIG Consortium partners.

Knowledge background

The GIG Consortium was formally started in March 2016. However, the Norwegian Computing Center and personnel at the partners have been deeply involved in developing methods and software for geophysical inversion for many years.

The GIG Consortium builds directly on the PCube software that has been implemented by the Norwegian Computing Center and Statoil ASA. PCube is a seismic inversion software that computes lithology and fluid probabilities from seismic AVO data. The PCUBE source code will be used as a platform for further development. The current version has a GUI on Windows. An invention by Norwegian Computing Center and Statoil is used by the PCube+ software. The invention is protected by Patent GB2463242 (Kolbjørnsen, O., R. Hauge and A. Buland 2012) held by Statoil. The source code repository for the PCube software and any use of this is to be considered as initial Consortium Results together with the rights to use this invention.

The Consortium will also benefit from the experience at Norwegian Computing Center from a range of projects involving geophysical data. The most prominent besides PCube is the development of the elastic inversion software called CRAVA based on Buland, Kolbjørnsen and Omre (2003). See also Ng, Dahle, Hauge and Kolbjørnsen (2008) for an application of CRAVA.

Norwegian Computing Center has developed and published various techniques for seismic inversion including Kjønsberg et al. (2010) and Hammer et al. (2012). Other relevant studies that Norwegian Computing Center has been involved in are inversion of CSEM (Kolbjørnsen et al. 2008 and 2012) and gravimetric data (Hauge and Kolbjørnsen 2015).

The use of geological knowledge to constraint the inversion results is a key element to obtain robust and fast results. Norwegian Computing Center has a long history of making stochastic models for geological surfaces, faults, depositional geometries and petrophysical properties. Background information can be found on Petroleum reservoir models (depositional geometries and petrophysics), COHIBA (surfaces), and HAVANA (faults).

The Uncertain Reservoir Evaluation (URE) initiative at NTNU is working with similar problems, and we follow their work closely. Both CRAVA and PCube are built on extensions of the theoretical framework developed there (Buland, Kolbjørnsen and Omre 2003 and Buland and Omre 2003). More recently, Rimstad, Avseth and Omre (2012) introduce theory that might be considered for inclusion in PCube, in particular depth trends for rock physics (already present in CRAVA) and wavelet uncertainty.