oa What would be the minimum subsurface information before making a decision to develop the field? A case study from El Toor field, Muglad Basin, Sudan

The El Toor field was discovered in 1996 and oil production started in early 2000. Cumulative production as of 2004 was 34 million stock tank barrels (MMSTB). El Toor is a fault-bounded anticlinal structure in the Muglad Basin, Sudan. The main reservoir consists of the sandstones of the Lower Cretaceous Bentiu Formation. The Upper Cretaceous Aradeiba E and F sands are secondary oil accumulations. Both sandstone reservoirs are layered and separated by continuous barriers over most of the field. After one year of sustained production, wells started to produce water. Both PCP and ESP are used for artificial lift. A team from the Sudanese Petroleum Corporation (Sudapet) has conducted a field development plan (FDP) to evaluate long-term production, reserve<br>estimation and techno-economics. The El Toor field FDP will be presented as a case study. The FDP study maximized our geological and reservoir knowledge of the field and specifically the lateral quality of the reservoirs. The subsurface information that was required for the FDP included: (1) seismic data control; (2) structure maps; (3) pay-zone thickness; (4) facies information; (5) petrophysical data; (6) core analysis; (7) fluid contact; (8) fluid properties; (9) water salinity; (10) estimated original-oil-in-place; and (11) well test analysis. The Greater Nile Petroleum Operating Company provided Sudapet with all the available subsurface data. The main problem was the lack of core and VSP data and accordingly data from neighboring fields was used. This resulted in uncertainty for the seismic velocity and difficulty in correlating core porosity to log porosity. The study recommended cutting cores and running vertical seismic profiles (VSP) in the future infill wells.