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* Chevron, Exxon gain on higher oil prices
* Trade tensions take a back seat; 3M, Boeing rise
* Micron warns tariff impact on results; Chipmakers slip
* Futures up: Dow 0.13 pct, S&P 0.02 pct, Nasdaq 0.09 pct (Adds comments, updates prices)
By Shreyashi Sanyal
Sept 21 (Reuters) - Higher oil prices looked set to help U.S. stock markets add to a week of gains on Friday as concern about a U.S.-China trade war moved further into the background.
Crude prices rose ahead of a meeting of OPEC and other large exporters that will focus on production increases as U.S. sanctions restrict Iranian exports, pushing shares in Chevron and Exxon Mobil higher before the bell.
The gains for oil followed a drop on Thursday after President Donald Trump demanded that Middle East producers get prices down.
"Oil prices are recovering from Trump's comments yesterday and will likely move to new 52-week highs," said Peter Cardillo, chief market economist at Spartan Capital Securities in New York.
Stock markets have been gaining steadily since the latest blows in a trade dispute between the United States and China on Tuesday, with all three major Wall Street indexes back in record territory after a rough few months.
Shares of Boeing and 3M, among those most exposed to a trade war, were marginally higher.
However, shares of semiconductor makers declined after top chipmaker Micron said U.S. tariffs on Chinese goods would weigh on its financial results for as much as a year.
Micron dropped 3.9 percent, while Intel fell 0.2 percent and Lam Research declined 1.1 percent.
"If a chipmaker like Micron warns about tariffs then it could certainly be impacting the semiconductors on the same worry," Randy Frederick, vice president of trading and derivatives for Charles Schwab in Austin, Texas.
At 8:36 a.m. ET, Dow e-minis were up 34 points, or 0.13 percent. S&P 500 e-minis were up 0.5 points, or 0.02 percent and Nasdaq 100 e-minis were up 6.5 points, or 0.09 percent.
Under Armour rose for the second straight session after J.P. Morgan upgraded the sportswear maker's shares.
The most significant changes to Wall Street's broad industry sectors since 1999 will take effect Monday, with many of the companies that powered the tech rally being reclassified.
Facebook, Google parent Alphabet, Twitter will all be reclassified as communications rather than tech stocks, while Apple will remain in the tech sector , where it will account for 20 percent of the index's market capitalization.
While any immediate market impact will be hard to gauge, investors are preparing for volatility as big institutional investors readjust their portfolios.
"The sector shake-up has been well telegraphed and the whole point of it is to not disrupt markets, so it won't have a huge impact and will only be reflected in high volumes today," said Frederick.
Shares of Facebook, Alphabet and Twitter were trading flat to marginally higher. (Reporting by Shreyashi Sanyal in Bengaluru)