NEW YORK ( TheStreet) -- Shares of Helix Energy Solutions ( HLX) are down by more than 7%, or roughly 80 cents, in early trading on Friday, after announcing that its oil and gas reserves are expected to be lower than previous expectations. As part of the effort by Helix Energy to divest its oil and gas assets, the company was conducting a mid-year review of reserves. Helix Energy said on Thursday that the review is expected to "reflect a significant downward revision" in proven reserves. The company also said on Thursday that plans to divest oil and gas business were likely to be slowed by the BP oil spill and the situation in the Gulf of Mexico. Helix has an offshore energy services business and its own exploration and production unit. Helix Energy cited updated well performance data for its Bushwood field, as well updated assumptions for other Gulf of Mexico oil and gas properties, in pre-announcing the reductions in the estimated volume of proved reserves. Helix Energy expects the final estimated proved reserves to be approximately 400 billion cubic feet of natural gas equivalents. In a previous 2009 year-end estimate, Helix has listed a reserve level equal to 578 billion cubic feet. In connection with the expected downward revision of proved reserves Helix Energy expects to record non-cash, pre-tax impairment charges in the range of $160 million to $180 million. -- Written by Eric Rosenbaum from New York. Follow TheStreet.com on Twitter and become a fan on Facebook.