* Sells UK North Sea assets for up to $3.8 bln to Chrysaor
* Sells stake in Thai gas field for $900 mln
* Chrysaor says to invest in wells Shell would not haveapproved
* Shell agrees to cover $1 bln in decommissioning costs
* Part of $30 bln in disposals planned by 2018 (Updates throughout)
By Karolin Schaps and Ron Bousso
LONDON, Jan 31 (Reuters) - Royal Dutch Shell announced two divestments on Tuesday worth $4.7 billionincluding selling a chunk of its North Sea assets toprivate-equity backed Chrysaor which will now become a top threeoil and gas producer in Britain.
The deals bring Shell's disposals to $12.5 billion sincemid-2015 as it aims for $30 billion in deals by 2018.
Shell is reducing debt accrued through its $54 billionacquisition of BG Group last year.
Shell agreed to sell a mixture of new and late-life NorthSea oil and gas assets, accounting for more than half of Shell'sUK North Sea production, to Chrysaor for up to $3.8 billion.
"(The deal is) providing a springboard for Chrysaor to bringnew investment and growth into the basin," said Shell UpstreamDirector Andy Brown.
The deal is expected to complete in the second half of theyear and will make Chrysaor Britain's leading independentexploration and production company.
Chrysaor is backed by EIG and Noble Group investment firm Harbour Energy. BMO Capital Markets Ltd advisedthe company, while Bank of America Merrill Lynch advised Shell.
Major oil companies such as Shell and BP arewithdrawing from the mature North Sea basin to instead focus onhigher-profit areas like Brazil or the Gulf of Mexico.
"We do have 6 or 8 wells we would be looking to sanctionthat the vendor was probably not looking to sanction," PhilKirk, CEO of Chrysaor, told journalists.
The package includes Shell's interests in Buzzard, north ofAberdeen, a relatively new field that feeds into the globalBrent oil benchmark, as well as a 10 percent stake in theBP-operated Schiehallion oilfield.
Other fields include Beryl, Bressay, Elgin-Franklin,J-Block, the Greater Armada cluster, Everest, Lomond andErskine, the companies said.
Shell agreed to cover $1 billion of the assets' total $3.9billion decommissioning costs, an often contentious issuebetween buyers and sellers of assets in mature areas.
Around 400 Shell staff are expected to transfer to Chrysaoron completion of the deal.
Shell also announced the sale of a stake in Thailand'sBongkot gas field to Kuwait Foreign Petroleum ExplorationCompany for $900 million.
"(These deals) will help Shell move past peak-gearing andcontribute to deleveraging," said RBC Capital Markets analystBiraj Borkhataria, who rates Shell's stock as 'outperform'.
Shell's London-listed shares were up 0.3 percent at 0910GMT. (Editing by Jason Neely)
