Study On Oil-Water Selective Plugging Agent System Of Temperature And Salt Resistance Gel Foam

The problem of water production in the Ordovician reservoirs in Tahe Oilfield has become more and more serious,and the increase in oil wells with high water cut has caused a serious decline in the productivity of oil wells.Water plugging technology is currently one of the most effective means to maintain stable production of high water reservoirs,but the high temperature and high salinity characteristics of the Tahe Oilfield limit the use of many plugging agents,and a small amount of temperature-resistant and salt-resistant plugging agent does not have the ability of oil-water selective plugging.Gel foam has excellent selective water shutoff performance,but it is difficult for existing systems to have both high temperature and high salt resistance at the same time.In this paper,by preferentially introducing polymers and foaming agents with temperature and salt-resistant monomers,a high-temperature and high-salt-resistant gel foam system is prepared to achieve the purpose of selective water blocking.In this paper,a high temperature and high pressure reactor was used to evaluate the gel time,gel strength and aging stability of the gel system,and rheological properties,gel strength,and characteristic group were measured using a rheometer,gel strength tester,and infrared spectroscopy,respectively.By screening different polymers and crosslinking agents,a gel system composed of 0.7%polymer Z4,0.3%hexamethylenetetramine and hydroquinone,and0.3%stabilizer was selected.It can be stable for 90 days under the conditions of 140℃and 200g·L^-1.The research results of the influence of temperature and inorganic salt show that the higher the aging temperature,the shorter the gelation time,and the gelation strength increases;the increase of the inorganic salt concentration,the gelation time is slightly reduced,and the gelation strength is almost unchanged.The gel system maintains good gel-forming properties within the range of 100-170℃and 120-300 g·L^-1 salinity,and exhibits excellent temperature and salt resistant.Subsequently,a foaming agent B with good foaming and foam stabilization performance,anti-adsorption performance,oil resistance performance and oil washing ability was selected.When the concentration is 0.3%,its FCI value can reach 237442 m L·s.The optimal gas-liquid ratio of the gel foam system prepared by using the optimized gel as the foam stabilizer and foaming with the foaming agent B is 1:1.The study of microscopic morphology shows that compared with ordinary foam,gel foam has smaller bubbles,thicker liquid film and stronger stability.The core displacement experiment was carried out using the fracture-cavity physical model simulating the Tahe Oilfield to evaluate the water-controlling and oil-increasing ability of the gel foam system.The optimization results of injection parameters show that when the average fracture width of fracture-cavity core is 125μm,the optimal injection rate of the plugging agent is 1.0 m L·min^-1 and the optimal injection rate is 0.8 PV.With the increase of the permeability difference of the parallel cores,the better the plugging effect on the high permeability layer;when the difference exceeds 23.4,the plugging agent all enters the high permeability layer.For fractured-cavity cores with a permeability of 147.0-163.2×10^-3μm²,the plugging rate of the gel foam to the water phase is always above 94%,and the plugging rate to the oil phase is below 30%,showing good oil and water selectivity.Microscopic visualization experiments show that the gel foam can selectively enter the hyperpermeable layer to form an effective seal.The gel foam can increase the recovery factor of the fracture model and the fracture-cavity model by 14.6%and 9.3%,respectively.