Production from multi-stage completion surpasses expectations

Background

The Campos Basin, found 80 km off the coast of Macaé, Rio de Janeiro, Brazil, has been explored for hydrocarbons since 1971. Advancements in directional drilling and multi-stage completions have enabled the development of previously uneconomical subsea reserves in this area. With these advancements, the Cretaceous section of Waimea accumulation of the South Campos Basin has begun to see development. Oil in the carbonate formation was discovered through the drilling of an exploration well in December of 2009.

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Challenge

The operator wanted to section the well into stages in order to effectively distribute acid stimulation over the entire lateral, and so required a multi-stage completion with proven isolation. In addition, water production at the toe of the well was a concern, so the operator was looking for a completion that could mitigate post-stimulation water production. The presence of hydrogen sulfide (H2S) and carbon dioxide (CO2) create further challenges to completion design in this formation, as in their aqueous forms, H2S and CO2 are acidic and will corrode standard steels. For their expertise in open hole, multi-stage completions, Packers Plus was called upon to help overcome the challenges that this operation presented.

Solution

The operator considered mechanical and inflatable packers to section the well into eight stages. They decided to use mechanical packers for their ability to hold higher pressures allowing for elevated stimulation pressure. The final design implemented field-proven Packers Plus RockSEAL® II dual-element, mechanical packers run in conjunction with premium screens. The system was manufactured from corrosion resistant alloy (CRA) to ensure its integrity after installation.

RockSEAL II packers are set by pressuring up the liner. However, because the operator opted to use screens, an alternative was necessary. To set the packers, an inner string was run into the well simultaneously with the liner to the landing depth. This inner string included a polished joint on either side of a perforated wash pipe. While pulling the inner string out, the polished joints were aligned with couplings located above and below each packer to form a seal, and fluid was pumped through the wash pipe in order to pressure up and set the packers.

Once the packers were individually set, the operator was able to acidize the well using a similar inner string to seal at the coupling above each stage with a polished joint and sequentially stimulate the eight stages along the 1,000 m horizontal wellbore. The acid stimulation was conducted at 1,500 psi, and was done in order to increase the effective permeability by cleaning the formation to ensure optimal oil recovery.

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Results

A drill stem test showed a potential production rate of 40,000 BOPD of 20° API oil with an expected flow rate of 20,000 BOPD. This result surpassed initial expectations related to the Waimea accumulation and provided a solid foundation for the commencement of the production phase for the operator. “This is one of the best production tests I have ever seen in my life,” said the operator’s General Director.

The success of this system has prompted the operator to drill more wells in the area using the same completion method.