Two Deepwater GOM Multizone, Frac-Packed, Intelligent Completions
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 19622, "Case History: Two GOM Multizone, Frac- Packed, Intelligent Deepwater Completions - How Success Was Achieved and the Associated Lessons Learned," by Stephen Jeu and Wayne Cunningham, Thunderbyrd Energy Services; Jacques Braile Salies, SPE, Petrobras America; Richard Jannise, SPE, Brad Beridon, SPE, and Brennan Oubre, Halliburton; and George Arnold, SPE, and Colton Puckett, SPE, WellDynamics, originally prepared for the 2008 Offshore Technology Conference, Houston, 5-8 May. The paper has not been peer reviewed.

Deepwater completions are defined as those in water depths greater than 1,500 ft. The extreme depth in itself presents challenges, but in addition to these, operators are seeking completion methods that will increase reliability and flexibility and will eliminate future interventions. The Gulf of Mexico (GOM) is a prime area for deepwater completions, and because of the extensive need for sand control, frac-packed completions have become the norm because they offer reliable sand control and long-term completion efficiency with higher sand-free producing rates and faster reserves recovery.

Project Description

The Cottonwood deepwater project is in the GOM Garden Banks Block 244, approximately 138 miles south of Louisiana in 2,118 ft of water. The sidetracking of Well B confirmed 130 ft 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. The wells are now Petrobras’ deepest and highest-pressure producing wells worldwide.

Gas and condensate production comes from Miocene sands at a depth of more than 19,300 ft. The complex structure and inherent stratigraphy along with the potential for compartmentalization provided multiple challenges for the geoscientists. The many deep and highly pressured reservoirs added further challenges to well-completion success.

The reservoir pressure in the G sand in Well A was measured at 15,125 psia, a 15.2-lbm/gal equivalent mud weight. A 15.6-lbm/gal completion brine was used to complete the wells, providing 200 to 250 psi of overbalance. The brine was composed of a blend of zinc bromide (ZnBr2), calcium bromide, and calcium chloride salts, to which 3% potassium chloride was added for improved clay compatibility, along with a corrosion inhibitor and a nonemulsifier. A 213°F bottomhole temperature was recorded with a wireline modular formation-dynamics tester (MDT).

Sidewall cores and MDT measurements confirmed that the highly laminated sands had a wide range of permeability, from 5 md to more than 2,000 md; an average of 100 to 200 md was used for completion and frac-pack design purposes. The maximum anticipated shut-in pressure (MASP) at the subsea tree was 11,500 psia and was 13,188 psia at the surface-controlled subsea safety valve (SCSSV) and 10,866 psig at the rig floor during the completion. The high MASP required deployment of the manufacturer's first two 15,000-psi-working-pressure horizontal subsea trees. The trees were installed successfully without significant incident. Fig. 1 shows the two trees.