Research On The Clean-up Technologies Of Water Block In Low Permeability Reservoirs

Low permeability sandstone reservoirs in China are very rich, which take 30 percent of the total gas and oil reservoirs. Low permeability undeveloped proved reserves take more than 50 percent of the total undeveloped proved reserves. Low permeability sandstone reserves take vital position and have huge development potential. With the reducing of conventional gas and oil reservoirs, people are paying attention to the exploration and exploitation of low permeability sandstone gas and oil reservoirs, which have critical significance to sustainable development of gas and oil reservoirs in China.Spontaneous capillary imbibitions and occluded liquid were studied. Formula of spontaneous capillary imbibitions force and formula of filtrate invasion depth near well bore formation were fetched when spontaneous capillary imbibitions force greater than liquid gravity. Experiments to clean up water block were carried out by using optimized the four most promising bio-surfactants such as rhamnoilpid, lipopeptide, lecithin high potency and sophorolipid. Spontaneous capillary imbibitions ability of cores were studied using an experimental apparatus of spontaneous capillary imbibitions designed by Drilling Research Institute of Shengli Oilfield, and relationship of mass imbibed versus square root of time and relationship of water imbibed versus square root of time in the ultra-low permeability, low permeability and the medium permeability ceramic core were studied. Mass imbibed versus square root of time curve and water imbibed versus square root of time curve in ultra-low permeability, low permeability and medium permeability ceramic core were fitted, and obtained fitted regression equation of spontaneous capillary imbibitions rate in the ultra-low permeability, low permeability and the medium permeability core. The spontaneous capillary imbibitions force in ultra-low permeability, low permeability and medium permeability ceramic core were calculated. The water blocking agents were applied to P11 level in low permeability reservoirs of Pinghu, the following conclusions:(1) Experiments revealed that relative gas permeability of sandstone cores decreased as increasing of water saturation. With decreasing of absolute gas permeability, it caused to seriously damage of water block.(2) The mixture of 0.05% rhamnoilpid, 0.8% mahogany sulfonate and 1% sodium carbonate was the best agents to reduce the surface tension. Capacity of reducing surface tension by the four optimized bio-surfactants from small to large was: lecithin high potency, lipopeptide, rhamnoilpid and sophorolipid.(3) Spontaneous capillary imbibitions force increased as gas permeability of cores increased. Values of spontaneous capillary imbibitions force in ultra-low permeability ceramic core were much larger than in low permeability ceramic core. Spontaneous capillary imbibitions force in ceramic core could significantly be reduced by adding bio-surfactants and their mixture. Decreased values of spontaneous capillary imbibitions force in ultra-low permeability and low permeability ceramic core were more evident than in medium permeability ceramic core, and the maximum decreased values attained 97.15%.(4) Core flow experiments revealed that displacement pressure and water saturation were decreased by adding surfactants, and the mixture of 0.05% rhamnoilpid and 0.8% mahogany sulfonate were best performance in decreasing displacement pressure and water saturation.(5) Core flow experiments of P11 reservoir in Pinghu gas and oil field revealed that relative gas permeability of cores were increased by adding water block clean-up agents in the same drilling fluids under the same displacement pressure, and increased values of relative gas permeability attained 10%; water saturation of cores were increased by adding water block clean-up agents in the same drilling fluids under the same displacement pressure, and decreased values of water saturation attained 5% to 30%.