Energy and mineral investor Xtract Energy has had to stop production at the Sarikiz-2 well operated by its Turkish business Extrem Energy after suffering problems with the pump.A mechanical failure meant the firm had to remove the pump from the well and replace components."Attempts are now being made to re-establish natural flow from Sarikiz-2 well," Xtract said Wednesday. "The initial promise of this well to produce commercial oil has not yet been fulfilled."The subsurface reservoir geology is proving more complex than originally anticipated and "the hydrocarbon migration path from the source rocks to effective reservoir traps is not yet properly understood".