A Comparative Analysis of Pre and Post Stack Lithology Prediction: Pre-Stack Wide Angle AVO Inversion and Post-Stack Sweetness Seismic Cube in Block 14, Offshore Angola

Mark Smithard¹ and Guy Delorme^2
1 ChevronTexaco, Luanda, Angola
² ChevronTexaco, Lagos, Nigeria

Angola Block 14 discoveries comprise Lower Miocene turbidite channel sands, which have proven to be prolific reservoirs; with one major field having just passed it's 100 MM Barrel milestone, and another six development areas approved and in varying stages of development.

Accurately predicting pre-drill the presence and depositional systems of these Lower Miocene sands has been the key' to success in Block 14,and various techniques have been brought to bear on the excellent quality 3D seismic to achieve the historic success of 5 billion barrels oil in place discovered in 10 years of exploration.

ChevronTexaco has developed a number of proprietary techniques for lithology and fluid prediction. Two such techniques are the Sweetness Seismic Cube, first described by Radovich & Oliveros in the Leading Edge; September 1998, and Wide Angle AVO to Lithology Inversion, described by Delorme & Smithard at AAPG International, Barcelona, 2003.

Both of these techniques have been utilised in the exploration of Block 14, maximizing success whilst minimizing expenditure. The theory behind each is elegant in its simplicity, and the resultant 3D lithology cubes startling in their resolution. However, no lithology prediction technique is a panacea, and none should be used in isolation. Each has its strengths and weaknesses.

Well results have proven the effectiveness of the lithology prediction cubes, allowing confident and high resolution volume interpretation, ready to be carried through to the development phase of the Block 14 fields.