UPDATE 2-Seadrill replaces CEO, looks to relocate management

* CEO to be replaced by Archer Ltd's Halvorsen

* Company looking at relocating management

* Board says hard to manage global firm from Norway

* London, Dubai, Singapore and Houston under consideration

(Recasts and writes through)

Oct 2 (Reuters) - Seadrill Ltd , the world's biggest driller by market capitalisation, said it plans to replace CEO Alf Thorkildsen with the head of its Archer Ltd affiliate, and is looking to relocate management outside Norway.

The Oslo-listed rig company, which has a fleet comprising of 67 units, including 19 rigs under construction, has been on an aggressive rig spending spree in recent years as it aims to keep up with fast-paced developments in oil exploration.

Seadrill said managing the company from the Norwegian city of Stavanger may constrain its aggressive growth plans, and said that Norwegian costs and the distance from Seadrill's core markets makes travel and logistics cumbersome.

Several locations including London, Dubai, Singapore and Houston are under consideration.

The company, in which Norwegian-born shipping magnate John "Big Wolf" Fredriksen holds close to 25 percent and is the company's chairman, said the board and Thorkildsen mutually agreed to terminate his contract.

Incoming CEO Fredrik Halvorsen, who has been interim CEO at drilling and well service firm Archer since January 2012, has worked closely with Seadrill's board and senior management, the statement said. He has also been CEO of Tandberg ASA, and has held senior positions at Cisco Systems Inc as well as McKinsey & Co.

Seadrill's modern fleet is in high demand after the BP oil spill, and the overall market is booming as oil firms, encouraged by rising oil prices, have increased exploration and have been forced to compete for available drilling capacity.

Thorkildsen has been Seadrill's CEO for the past four years.

Under his leadership Seadrill overtook Transocean as the world's top rig company by market value. Revenue increased three-fold between 2007 and 2011 although there were patches of gloomy market conditions during that period.

Last month, he said Seadrill will revive plans to list its Brazil-based Seabras unit next summer as it seeks funds to further expand its growing rig fleet.

Shares of the Oslo-listed company have risen close to 40 percent in the past 52 weeks, comfortably outperforming its peers.

(Reporting by Thyagaraju Adinarayan in Bangalore, Editing by Edwina Gibbs)

((thyagaraju.adinarayan@thomsonreuters.com)(within U.S. +1 646 223 8780)(outside U.S. +91 80 4135 5800)(Reuters Messaging: thyagaraju.adinarayan.thomsonreuters.com@reuters.net))