Summary: FORCE Seminar: Fluid and Lithology Prediction from Seismic, the Current Status

Summary: FORCE Seminar: Fluid and Lithology Prediction from Seismic, the current status September 27-28th 2004 at the NPD

The FORCE Seminar “Fluid and Lithology Prediction from Seismic, the current status” proved to be a very popular event. Attendance was amongst the best ever for a FORCE seminar with a total of 149 attendees (including presenters). The attendance comprised 103 representatives from oil companies and 46 from service companies. Over the two days there were a total of 22 talks including 11 from oil companies (including the key note speech) and 11 from service companies. 87 people attended the seminar dinner at “Røde Sjøhus”, which was a great opportunity to relax and network.

Key Note Terje Dahl opened the conference with an excellent Key Note speech. He described some of Statoils learnings and best practices. To cite a few:  Time-lapse feasibility studies are a default for Statoil – the case has to be made for why not to do so. Statoil have demonstrated $750MM of value creation through time-lapse application.  Historically, many fluid effects were “processed out”. For example the flat spot at Gullfaks only became evident after reprocessing, early processing attempts had largely removed the anomaly largely due to the lack of expectation for such a response.  Amplitude conformance to structure often requires advanced process such as Pre-SDM to become unambiguous.  Use of OBC data has proved highly effective at discriminating fluid effects from pitfalls.

 Split Pdiscovery in a fluid and a lithology part, and show the effect of each type of analysis (e.g. PS, AVO, SBL, etc.) on the posteriori probabilities.  We need continual improvement in data processing and we need more geophysicists!

Seismic Data Processing. Sean McQuaid (Geotrace) and Henning Hoeber (CGG/BP) gave perspectives on data processing best practices for fluid and lithology prediction. In Hennings words the main goal “is to deliver interpretation-ready data”. A synopsis of key points from Sean and Henning’s’ talks is as follows:  Controlled phase processing for all offsets and angles (this is easy to get wrong!).  Ensure that incidence angles are well understood  Offset amplitude scaling via ray-trace modelling to correct for spherical divergence and convert the amplitudes to reflectivity  The importance of getting the phase and timing right and minimize the differences across the offsets.  Q.C. of residuals velocity and time alignments  Bi-spectral picking and sampling density to try to flatten the velocity hockey-stick effects  Amplitude/spectral balancing with offset  Dip-consistent filtering  Integration: necessity for the interpreter to take part in the processing step that will lead to its interpretable cubes. Paddy Smith (WesternGeco) presented a somewhat different approach with WesternGeco’s “well driven seismic” (WDS). This technique incorporates the well log information, velocity, VSP etc. throughout the processing flow to link well and seismic data through a common earth model. The walkaway VSP data allows a measure of the anisotropy. A very good AVO match between the predicted and actual was obtained for an Oseberg field case study.

Inversion Emerging approaches to inverting for the “third term” or a density term in addition to compressional and shear velocity emphasized the importance of anisotropic processing. Peter Mesdag of Fugro-Jason gave an excellent introduction to the theoretical aspects of resolving for the third term and was followed by a Mexican case study from Veritas and further insights from Odegaard. There were clearly some different viewpoints and approaches to this issue and discussions were nicely “tee-ed” up if not resolved. Applications for density inversion have to date more applications outside Norway where amplitude anomalies due to low gas saturations are a common problem – this is less evident in Norway and more common in younger Tertiary basins. Marcel Zwaan (Shell) gave an excellent talk emphasising the importance of proper quality control steps in data processing to effectively invert seismic data.

Non-Seismic Technologies & Data Management Kenneth Duffaut’s paper on well seismic FUSION Statoil's experiences with described the challenges of bringing pre-stack seismic data to the interpreter’s desktop. In 12 months from time it will be an intriguing to hear the results of Statoil’s pilot project involving 30 interpreters and their projects with the software. How effective will the data management be? And how effectively will the interpreters be engaged?

There have been notable successes in application of the Seabed Logging with well results generally validating SBL predictions. However it clear that it is important to understand the appropriate conditions for application of the technology its inherent non-uniqueness.

Rock Physics In the world of rock physics incorporating depth trends and the effects of diagenetic cementation such as quartz cementation is clearly of prime importance for the Norwegian continental shelf. Hans Martin Helset (Geologica/Hydro) and Trond A Seland (Statoil) addressed the technical approach, which tied very well with the practical application to reservoir development at Ellida (Marie Schneider (Statoil) and Brackin Smith (ConocoPhillips).

Case Studies We had the privilege seeing two important case studies in a public arena for the first time. The first was Ellida, a prospect that exhibited a very clear flat spot in the Nise section and attracted strong interest in the Norwegian 17th round. Well results show the anomaly was caused by oil in a very poorly developed reservoir - in contrast with many peoples’ pre-drill expectations. Two papers on Ellida were presented, one by Marie Schneider of Statoil and the second by Brackin Smith of ConocoPhillips which revealed many insights into the causes of the Ellida seismic anomaly. The second case study “first” was Olav Barkved’s paper on the Valhall “Life of Field Seismic” project. The importance of this paper was the clear demonstration of examples of production related time-lapse responses after a 6 month period using the Valhall permanent installation ocean bottom cables. This will surely be good news for the future of time-lapse technology.

Jurgen Hoffman (RSI) discussed the use of seismic attributes for fluid and lithology prediction for the static case and David Gawith (EarthModels Ltd/Paladin) for the dynamic (time lapse) perspective. Both papers discussed the value of a multi-attribute approach with classification techniques such as neural networks and Kohonan self organizing methods.

Seminar Questionnaire A questionnaire was handed out at the seminar seeking feedback on key areas for research focus in the arena of Fluid and Lithology Prediction from Seismic. The “top ten” were as follows: 1. Rock physics – integration of core data and well measurements 2. Integration of geophysical and geological reservoir models 3. Shear wave interpretation 4. Prediction of Hydrocarbon saturation – dynamic 5. Increased resolution 6. Seismic Inversion 7. Prediction of Hydrocarbon saturation – static 8. Handling of overburden effects 9. AVO – processing 10. Shear wave processing

Learnings for future seminars:  There was energy and scope for a lot more discussion than we allowed for  We should strive to have a greater bias in the papers from oil companies.

The challenges of applying best practices:  Effectively integrating data processing, inversion and interpretation to optimize results  Engaging interpreters in using pre-stack data.  How to justify the cost to the decision makers for_ - Walkaway VSP’s (valuable for anisotropic processing) - OBC or SBL to validate hydrocarbon indicators. - Time-lapse surveys.

Acknowledgements: Special thanks are due to:  The organizing committee of John Hughes (ConocoPhillips, Lead), Arild Haugen (NPD), Nils Bakke (Statoil), Per-Gunnar Folstad (BP), Alain Riou (Total), Andy Roberts (Paladin) and Aart- Jan Van Wijngaarden (Hydro)  Gro Galta for looking after many of the administrative details.  Paladin and ConocoPhillips for co-sponsoring the dinner (and Nils Bakke for delivering the “Takk for Maten”).  NPD for hosting the event  To all the presenters including Terje Dahl for the excellent key note speech