Classified Prevention Of Water Channeling In Heterogeneous Reservoirs

The differences among the physical properties of fluids and the permeability heterogeneity of reservoirs cause the water channeling,which is a common and serious problem in oilfields,in most heterogeneous reservoirs after a long-term oil production.The urgency of treating water channeling makes the prevention technologies develop fast.Now,there exists a great variety of methods.However,there is no reasonable and scientific method to select a suitable prevention technology for water channeling to a certain reservoir,the effects for treating water channeling are still poor in most heterogeneous reservoirs.In order to increase the rationality and accuracy when selecting the prevention methods for water channeling in different type reservoirs,the classification of water channeling and the method of prevention technologies selection in heterogeneous reservoirs are studied.Indoor experiments are used to study the strength of water channeling in inner heterogeneous of layer reservoirs and inter-layer heterogeneous reservoirs respectively.Water channeling coefficient is proposed as the characteristic parameter,which reflects the strength of water channeling.According to relationships between water channeling coefficient and heterogeneity of reservoirs,the classification of water channeling and the different treatment methods are discussed in this paper.Combining the plugging strength of profile control agent with the flow condition of remaining oil,the performances of profile control agent are confirmed,which improves the pertinence to selecte a profile control agent for the certain reservoir.And the classification method for dealing with water channeling in heterogeneous reservoirs is formed.According to this method,the adaptabilities both of nano-microsphere and polymer gel in inner heterogeneous reservoirs are evaluated.As to the prevention mathod of water channeling in the inter-layer heterogeneous reservoirs,the potential for the subdivision of layer series technology is evaluated and its standard is confirmed.The results show that the stronger the heterogeneity is,the heavier the water channeling in inner heterogeneous of layer reservoirs is.Moreover,the existence of fractures and the high-rate production strengthen the degree of water channeling.If the inner permeability variation coefficient is less than 0.35(?),the water channeling can be prevented by controlling the water flooding rate below 5.0 m/d.But if the inner permeability variation coefficient is more than 0.35(???),the water channeling should be treated by selecting the suitable plugging agent for deep profile control.The plugging agents are classified on the basis of the requirement that the plugging ability of profile control agent should be higher than the flow condition of residual oil.So the suitable water channeling prevention technology can be selected in different heterogeneous reservoirs,which forms the classification method.The gel testing device can simulate the strained condition of gel in the pore throat and test the pluging strength,viscous resistance and stability.According to the comparison between the plugging ability of Nano-microspheres and the flow condition of residual oil,the Nano-microspheres with the average particle size of 100 nm can plug the water channel with the permeability range from 25×10-3?m2 to 1300×10-3?m2,and it is suitable to preventing water breakthrough in the reservoirs with the medium heterogeneity,which means the permeability variation coefficient should be below 0.70.The material strength of polymer gel,which has the optimized gelation time,is 0.31 MPa.And the plugging strength in different permeability cores is as high as 30MPa/m,which can make the residual oil in the reservoirs with the minimum permeability of 5×10-3?m2 be displaced.As the same evaluation method as the Nano-microspheres,the polymer gel is suitable to preventing water breakthrough in severe heterogeneous reservoirs.In vertical multi-layer heterogeneous reservoir,the degree of water channeling improves with the increasing of inter-layer heterogeneity.The subdivision of layer series technology has the good potential to preventing water channeling in inter-layer heterogeneous reservoirs.The water flooding recovery decreases slowly first with the increasing of permeability variation coefficient,but it declines rapidly when the permeability variation coefficient exceeds 0.50.So the water channeling can be prevented by avoiding the permeability variation coefficient over 0.50,which can be realized by subdivision of layer series technology.But if the permeability variation coefficient is more than 0.50,the water breakthrough should be treated by layer subdivision or profile control,and the effect is better if the treatment is done in the early stage of oilfield production.