One of British BG's biggest cash cows could disappear in an instant, as Shell's acquisition bid on BG could open up for a new bidding war on the rights to the major Karachaganak gas field in Kazakhstan. The field has till now represented a key source of value creation for BG - gas from the field has accounted for 15 percent of the company's gas output and nine percent of BG's profits, according to the Wall Street Journal.