Testing a Heavy Oil Well in Ultra Deep Waters: Challenges Overcome by the State of Art Technology in Atlanta Project, Santos Basin, Brazil

Abstract

Testing heavy oil in offshore wells is, by itself, a challenge. But testing heavy oil, highly viscous (220 cP at the reservoir temperature), in ultradeep waters (1550 m), in a horizontal well equipped with a long open hole horizontal gravel pack (800m), using an electrical submersible pump (ESP) deployed in a slant section at 75 degrees is really a big challenge. Atlanta is a post-salt oil field located 185 km off the coast of Rio de Janeiro. The field was discovered in 2001. The appraisal plan, started at the same year, included a deviated well to test the eocenic sandstones. A cased hole gravel pack was installed. The 90m interval tested, showed an unconsolidated sandstone, with high porosity (35%) and high permeability (5D). However, the oil is heavy and viscous (14° API and 228 cP in reservoir conditions), very acidic (TAN=9.8). In 2006, a long horizontal well was drilled to validate the field development concept and evaluate the potential of this kind of well construction. However, crucial problems were faced in the drilling and completion phase, which included, directional control problems, massive fluid loss in the reservoir section, use of a LCM pill, premature screen during the open hole gravel pack operation, leaving a SAS completion. Even after these problems, it was decided to maintain the well test. An ESP was run in the DST string. After some flow (approximately 20 h), the screens were plugged resulting in their failure and therefore sand/solid production. The ESP locked with the produced solids and overheated, getting burned. The partially conclusive DST showed a severe damaged well, with high skin of 40. The well was abandoned without carrying out its objectives, and the horizontal completion was not fully evaluated. The bad experience compromised the reliability of the project. However, in 2012, another operator decided to revisit the lower completion and testing procedures. After considering technology improvements and the lessons learned in the past operations, an extensive testing program was stablished and carefully executed. In 2013 a well was drilled, completed and successfully tested, with the ESP near the top of the reservoir. The zero skin completion and high productivity of the well encouraged the operator to drill and test the second well, this time using the ESP above the sea bed, inside the drilling riser, which included more difficulties due to the low temperature at that position. This paper presents the main challenges and details on how they were overcome by the successful completion and testing of the first two production wells encouraging to move on to the next phase.