PetroNeft, an oil and gas company with concessions in Russia, has been forced to postpone a fracture stimulation, or 'fracking', programme at its Lineynoye field after a mystifying fall in oil production at one cluster of wells.The good news is that the Lineynoye Pad1 wells have responded to the water injection programme started last summer, resulting in a halt in the production decline some wells had been experiencing and in some cases there has even been an increase in output.The bad news is that the Pad2 wells have seen higher than expected well decline rates and the company is now trying to work out why.Total production at the Lineynoye field development programme had got as high as 3,000 barrels of oil per day (bopd) at one stage but in recent weeks has tailed off to 2,300 bopid.PetroNeft thinks it will be at least six months before it completes the necessary studies. Until then development will be focused on its Arbuzovskoye field.The company's share price had plummeted 34% by 12.03pm on the news. Over the past 12 months the stock has now dropped 85%.BS