Jan 11 (Reuters) - Exxon Mobil (XOM.N) on Tuesday launched the sale of shale gas properties stretching across 27,000 acres in the Appalachian basin of Ohio, the company confirmed, part of an ongoing divestiture of U.S. assets. The top U.S. oil producer is marketing 61 wells that last year produced around 81 million cubic feet per day equivalent (mmcfd) of natural gas, according to a marketing document viewed by Reuters. The sale includes another 274 wells operated by other companies. A sale could value the assets at around $200 million based on current natural gas prices and existing production from the wells, a person familiar with the matter said. "ExxonMobil is providing information to third parties that may have an interest in the assets, but no agreement has been reached and no buyer has been identified," said spokeswoman Sarah Nordin. Operations are continuing, she added. The company in 2020 took about a $20 billion writedown on properties, primarily purchased with subsidiary XTO Energy a decade earlier. It removed gas assets in Appalachia, the Rocky Mountains, Oklahoma, Texas and elsewhere from its development plan after the writedown. The Ohio properties produced around 250 mmcfd of gas in 2017 and are among assets that Exxon put on the market as it focuses development in Guyana, offshore Brazil and Texas"s Permian Basin shale field. read more U.S. natural gas futures settled at $4.219 on Tuesday, up more than 80% since the end of 2020. The company three years ago set a goal of raising $15 billion from asset sales, and last year accelerated its marketing efforts as energy prices recovered from the pandemic. (This story corrects natural gas settlement price to $4.219 from $2.249 in paragraph 7)