Drilling the Undrillable: Atlanta Field Heavy Oil in Ultra Deep Water

Abstract

AbstractThe development of heavy oil (14 API) in ultradeep waters (1550 m), in a reservoir 800m bellow mud line is a technological challenge all over the word. This paper will present the solutions applied successfully to drill, gravel and test two horizontals wells under these extreme conditions.Atlanta field is a post-salt oil field located offshore Brazil, in the Santos Basin, 150 km south of Rio de Janeiro. The water depth has approximately 1550 m, the reservoir sits 800 meters bellow the mudline, has an unconsolidated sandstone with an average 38 % porosity with high permeability and a 14 API oil. This paper presents most of the challenges the operator had to overcome to drill, gravel and test two wells already with great success. Both wells have a casing program composed by 36″/16″/11 7/8″ and an horizontal section of 800m drilled in 9½″. Due to the 14 API oil the artificial lift method chosen was ESP (1500 HP) installed at an inclination of 75 degrees of the well. To install the pump the well profile was built with a slant section of 100 m with maximum DLS of 1 degree/100ft to avoid fatigue during the operation, but also a maximum dogleg of 5 degree/100 ft to avoid damages to the pumps while running into the wellbore. To be able to achieve the constrains imposed by the ESP, from mud line at 1550 m to the top of the reservoir at 2330 m the well profile design had to achieve a 43 inclination during the riserless drilling section of the well, the techniques applied are described in details in the paper. The next challenge was to drill the horizontal section with a very narrow margin from collapse to fracture of the well, all the procedures regarding drilling fluids and drilling techniques are presented. The 800m horizontal section was drilled in 9½″ to allow the use of 6 5/8″ premium screens to increase production. To guarantee a minimum content of sand in the produced oil with the objective of increasing the life of the ESP the well was gravel packed. Due to a small fracture gradient of the previous shoe 11 7/8″ the gravel was performed successfully with a special propant with very low weight, again the details are presented. The wells were tested with two different positions of the pump: one at the bottom of the well, and other at the sea level just above the BOP. The objectives of the test were to compare the performance of the reservoir with the pumps in two different positions, but also to study the flow assurance problems that may occur after programmed or non programmed stops of the future production system. All the results and main conclusions are presented.The excellent results obtained from the drilling, gravel and testing of both wells, which are presented in this paper, confirms the potential of Santos basin’s Atlanta field.