Vanoil sees Sudan-like features on Rwandan seismic

By OGJ editors

Vanoil Energy Ltd., Vancouver, BC, said that 2D and 3D seismic to be shot in the second and third quarters of 2012 will lead to more advanced reservoir characterization techniques being applied for the purpose of choosing an optimum drillsite on blocks 3A and 3B in Rwanda.

Vanoil in 2011 contracted Sproule International Ltd. and Geoseis Inc. to interpret 2,850 line-km of seismic data. The data included 2,000 line-km of legacy seismic shot in 1975 by Chevron that has proved to be of immense value after reprocessing for structural analysis but lacking the offset range for amplitude analysis.

Vanoil acquired 850 line-km of prospect grade seismic data in 2010 and 2011 at a cost of $8.5 million that has adequate offsets for the purpose of mining geological data from seismic amplitudes. The data have been relative amplitude and amplitude versus offset processed by Statcom Ltd.

Structural leads identified by Sproule and Geoseis are coincident with some of the AVO anomalies. This correlation has derisked and ranked the Sproule-identified 27 leads. The complete seismic data set has been further subjected to advanced reservoir characterization techniques ranking the 27 leads by their fault sealing and hydrocarbon charge attributes.

This has led to delineation of a 1,700 sq km area on the south and southwest flanks of the South Anza basin. The area is an analog to the Melut basin in Sudan and is characterized by 15 leads that are grouped into eastern, southern, and western lead areas.

The eastern lead area bears strong similarities to Adar-Yale oil field in Sudan. It is composed of a string of six leads that start from the South Anza basin depocenter up along rollover structures and ending on a horst block of a Karoo graben. Stratigraphic sequence analysis of seismic data and correlation near the Bahati and Endela wells, which are 15 km from east focus leads and 20 km from the western focus leads, respectively, clearly correlates the likely source and possible reservoir facies.

This is a fundamentally different interpretative approach, AAPG approved, from past practices due to advent of seismic sequence and facies analysis techniques in the 1980s. The structural considerations alone have been the criteria for choosing drillsites in past failed exploration programs, Vanoil said.

In order to properly place the more than 75 sq km, $3.5 million 3D seismic survey on one or two of the 15 leads, a 78 km, $800,000 2D seismic survey has been designed and shot in Block 3B along a string of six leads identified 15 km from the Bahati well. The 2D survey was to be shot in the last quarter of 2011, but heavy rains and adverse health and safety issues led to its postponement.

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