WARRI — Oil and gas investment in Nigeria fell from about $26 billion in 2014 to about $2 billion a year by 2023, the Chief Executive of the Nigerian Upstream Petroleum Regulatory Commission, Oritsemeyiwa Eyesan, said at an industry conference in Warri. She said the country lost skilled geoscientists and petroleum engineers during that period and called for those skills to be rebuilt as new investment returns.