When OPEC sits down on Thursday, keeping the price of Brent above $50 (to avoid a budget catastrophe and social upheaval in Saudi Arabia) and below $60 (to prevent US production from going exponential), will be just one problem the cartel nations and various hangers-on will be desperate to solve. A much bigger one, literally, is the problem that led to this week’s OPEC meeting in the first place, and years of headache for OPEC and non-OPEC nations: a record global oil inventory glut.