SS: Thunder Horse and Atlantis Deepwater Frontier Developments in the Gulf of Mexico: Thunder Horse Takes Reservoir Management to the Next Level
Authors: Arnold Greg , Cavalero Sean R. , Clifford Peter John , Goebel Evelyn M. , Hutchinson Dave , Leung Hong , Paclibon Eileen Nunez , Weiss Troy Don , Grass D.B. 
Published: July 2010

Abstract
This paper describes the achievements of reservoir and well management during the first two years of production from Thunder Horse in the Deepwater Gulf of Mexico (DW GoM). Thunder Horse is a subsea development of several large and complex reservoirs. It came on production in June 2008 and had ramped up to a field rate in excess of 250,000 boe/day from nine producing wells by December 2009.
Successful ramp-up and high first year efficiency were achieved using advanced technology and multidisciplinary interaction. Lessons were learned in sand management and flow induced vibration and well management problems were mitigated.
Thunder Horse has a flexible development concept, particularly with regard to water injection. This reflects its high initial subsurface uncertainty, especially regarding compartmentalization and the degree of aquifer support. The value of the flexible approach has been demonstrated. However, it makes strong demands on rapid learning. This paper describes how this learning has been achieved and how it is being used to drive the flexible development.
Surveillance data and analysis were the keys to rapid definition of the subsurface risks. Data from permanent pressure gauges were analyzed using advanced techniques. Reservoir simulation models were calibrated to the full set of real time data. Temperature and oil composition data provided additional controls. Results demonstrated that faults in Thunder Horse, though sealing in some places, do not in general cause compartmentalization. They can even provide vertical connectivity to aquifer in deeper sands, allowing a high degree of energy support. At the same time it creates complex paths for water movement. This changes the role of water injection in large areas of Thunder Horse from early pressure support to later optimization of an aquifer-dominated sweep.

Introduction
Thunder Horse, located in the Mississippi Canyon area of the Gulf of Mexico (Figure 1), was discovered in July 1999. The Thunder Horse co-owners have announced1 recoverable volumes which make Thunder Horse one of the largest deepwater fields discovered in the Gulf of Mexico or globally.
Thunder Horse is in water depth of 5,800 to 6,500 ft. It utilizes subsea wells producing to a permanently moored floating semisubmersible production, drilling and quarters facility (PDQ.) The nameplate oil production rate is 250,000 stb/day. The PDQ also has facilities for more than 200,000 bbl/day of water injection.
Thunder Horse consists of two distinct geological structures: Thunder Horse South (THS) and Thunder Horse North (THN), shown in Figure 2. Each structure contains several reservoirs, as shown in Figure 3. Production from THS started in June 2008, followed by THN in February 2009. Plateau production of approximately 250,000 stb/day has been maintained since THN came on production. By December 2009, 9 wells were on production: 4 in THS and 5 in THN.
Thunder Horse oil is sweet with gravity of approximately 30 degrees API and it is undersaturated with a GOR of about 1,000 scf/stb. The bubble point pressure is less than 5,500 psi in most areas, compared with initial pressure greater than 13,000 psi, giving a high degree of undersaturation, as seen in many DW GoM fields2.