Case Histories of Unique Multi-Zone Intelligent Deepwater Sand-Control Completions - How Successes Were Achieved and the Associated Lessons Learned
Authors: Jeu Stephen J. , Cunningham Wayne , Salies Jacques Braile , Jannise Richard C. , Beridon Brad Robert , Oubre Brennan Paul , Arnold George Steven , Puckett Colton Tyrel 
Published: October 2008

Deepwater completions are defined as those executed in water depths of greater than 1,500 feet. The extreme depth in itself presents challenges, but in addition to these, operators are continuing to seek completion methods that will increase reliability, flexibility, and eliminate future interventions ? strategies which further add to well-completion complexity.

The Gulf of Mexico is a prime area for deepwater completions, and because of the extensive need for sand control, frac-packed completions have become the norm as they offer reliable sand control and long-term completion efficiency with higher sand-free producing rates and faster reserve recovery. The application of intelligent well designs provides operators with other advantages with respect to cost-effective development of multiple, smaller reservoirs.

Operators are continually faced with the need to balance the cost and risks associated with well complexity against the cost and risks of future interventions - both of which are impacted by ever-increasing day-rates and the tight availability of rigs and multi-service vessels needed for intervention.

The challenge of combining intelligent, multi-zone completions with sand control is further complicated when dealing with deep, high-pressure deepwater wells. Lessons are being learned every day in these arenas.

This paper summarizes two examples of multi-zone, frac-packed, intelligent 15k deepwater completions that were recently undertaken in the Cottonwood project in the Garden Banks Block 244 operated by Petrobras America. Measures taken to streamline and mitigate risk during rig operations and to reduce non-productive time through inspection and quality-control efforts will be discussed.

Project Description and Overview

The Cottonwood Deepwater Project is located in the Gulf of Mexico's Garden Banks Block 244, approximately 138 miles south of Louisiana in 2,118 feet of water. The prospect consists of Pliocene and Upper Miocene turbidite sands that have filled in pockets on the flank of a remnant salt feature. The complex structure and inherent stratigraphy as well as the potential for compartmentalization provided a myriad of challenges for the geoscientists. The many deep and highly-pressured reservoirs added further challenges to the success of the well completions.

In 2005, Petrobras America acquired a 100-percent working interest (WI) and became the operator of the block. Mariner Energy joined as a 20% WI partner prior to the sidetracking of Well ‘B’. The sidetrack confirmed 40 meters (130 feet) of natural gas and condensate pay.

In September 2005, Petrobras America announced an ambitious plan to drill an additional well, complete both wells, install production facilities, and begin production by early 2007 - less than 15 months from project sanction. Petrobras achieved this timeline, and the wells are now Petrobras' deepest and highest-pressure producing wells worldwide. Cottonwood was developed as a subsea development with a 20-mile flowline to a production platform in East Cameron block 373. The planning schedules are shown in Tables 1 and 2.