“To produce the most viscous oil from completely unconsolidated sandstone in ultra deep waters”. This summarizes the challenges to construct the wells to exploit the Atlanta field, Santos Basin, Brazil. The ultra deep water of 1550m, the use of a powerful subsea ESP with 1,600 HP, the need of long (850 m) open hole horizontal gravel pack (OHHGP), the low burial depth (800 m) resulting in low reservoir temperatures (100 F) and extremely low fracture gradient (0.50 psi/ft), the highest acidity of a crude (TAN=9.8) are some of the difficulties that had been overcome to drill, complete and test the first 2 production wells of the Atlanta Field.
Atlanta is a post-salt oil field located 185 km off the coast of Rio de Janeiro. The field was discovered in 2001 and during the same year a deviated well was drilled to test the eocenic sandstones. A cased hole gravel pack was installed in 90m of perforated interval. The completely unconsolidated sandstone showed high porosity (36%) and high permeability (5D). While the rock properties are excellent, the oil is heavy and viscous (14° API and 228 cP in reservoir conditions), with the highest acidity registered (TAN=9.8).
In 2006, a horizontal well was drilled to test the full potential of this kind of construction, which included and OHHGP, and to validate the field development concept. However, crucial problems were faced during the drilling and completion phase. Directional control problems led to two sidetracks. The horizontal section experienced massive fluid loss. Only part of the screens was run in the open hole. The attempt to pack the screens, with alpha-beta waves, resulted in a premature screen out leaving a SAS completion. Even after these problems, the well was tested, with solid production causing the ESP failure. The partially conclusive DST showed a severe damaged well, with high skin of 40.
The bad experience in constructing a horizontal well in these challenging conditions compromised the reliability of the project. But in 2012, a new operator decided to revisit this project. After considering technology improvements, an extensive preparation and a complete assessment of past operations were performed. Finally, in 2013 and 2014, 2 wells were drilled and, using the best technologies, 100% packed in the full horizontal length (800m) drilled. Both wells were tested showing zero skin.
This paper presents the main challenges and how they were overcome by using the best sand control techniques, resulting the successful construction, gravel packing and testing the first two production wells, recovering the reliability of the project and encouraging to move on to the next phase.