By Solace AMANKWA Tullow Oil, one of Europe's largest independent oil exploration and production companies, has upgraded its estimate of reserves at its Tweneboa field in Ghana by 60%. The field, according to Tullow, could prove to be much bigger with the tendency to be upgraded further. According to the company, the successful drilling in the past year showed potential resources of 4.5 billion barrels across all its prospects and fields in Ghana. BusinessWeek gathered that the company plans to develop the Jubilee field well gradually, starting at a rate of about 60,000 barrels a day, at which point the cash will start to flow, helping to finance future investment to raise production between 250,000 to 300,000 barrels per day. It had also agreed on a framework deal to bring in China National Offshore Oil Corporation (CNOOC) and French oil company, Total, as equal partners in its Ugandan assets, which would involve Tullow selling more of its share than earlier planned. Exploration d...