Study On Water Decreasing And Oil Increasing Technology Of Medium-high Water Cut Oil Wells In Loose Sandstone Reservoirs

At present,most oilfields domestic and overseas have entered the middle and late stages of development,and the exploration difficulty of petroleum industry is increasing day by day.It is necessary to develop some oilfields which are difficult to develop.Chinese offshore oilfields have a large amount of reserves and good development prospect,among which loose sandstone reservoirs are the main reservoirs.The rock skeleton of this kind of reservoir is unstable,and reservoir damages are easy to occur in the production processes.When the development enters middle and late stages,the situation of medium-high water cut generally occurs in oil wells.Therefore,it is hoped that the reservoir damage can be relieved under the premise of protecting the rock skeleton,the water cut of oil wells can be reduced,and the productivity can be improved,which contributes to the increase of oil and gas reservoir productivity.Sandstone matrix acidizing is an essential strategy to maintain or increase productivity or injectivity of hydrocarbon wells.However,for loose sandstone reservoirs,conventional acid system is easy to destroy rock cementation strength after acidizing,which leads to sand production.The acid injected by general acidizing technology will give priority to high permeability water layer.Over-reformation of water layer will further aggravate water cut rise and affect the effect of acidizing stimulation.In this paper,a new type of low damage and moderate dissolution multiple chelating acid system and a selective plugging agent SA-1D with diverting and water-control are developed.Multiple chelating acid can inhibit the reservoir damage of particle migration and protect the rock skeleton.Selective plugging agent SA-1D is used for diverting of acid solution to achieve uniform acid distribution and reducing water cut.Finally,a set of precipitation and oil stimulation technology suitable for medium-high water cut oil wells in loose sandstone reservoirs is developed.The main research work and achievements of this paper are as follows:(1)Based on reservoir data and core laboratory tests,the reservoirs damage factors are analyzed from the aspects of geological reservoir characteristics,rock and mineral characteristics.The degree of reservoir damage is calculated by establishing a particle migration model,which provides a technical idea for analyzing the damage factors and degree of similar reservoirs.(2)For the problems of loose cementation and particle migration damage in target reservoir,a new multiple chelating acid system with low damage and moderate dissolution was developed.The system can inhibit particle migration damage and protect loose reservoir skeleton by reducing the dissolution of clay minerals with larger specific surface due to physical and chemical adsorption,and strengthening the dissolution of quartz,feldspar and other matrices.It has certain popularization and application value for stimulation and transformation of similar reservoirs.(3)For the problems of strong reservoir heterogeneity and medium-high water cut,a new type of diversion and water-control material,called selective plugging agent SA-1D,has been developed.When combined with acid solution for diversion acidizing,it has the dual functions of acid uniform distribution and water control.The particle size of the material is easy to adjust,which can adapt to reservoirs with different pore throat sizes(0.1-300?m).Therefore,it can meet the needs of dewatering and oil increase of most reservoirs.(4)According to the offshore oilfields operation conditions,target reservoir characteristics and the design requirements of dewatering and oil-increasing technology,a diversion mathematical model is established to optimize the in-site operation parameters of selective plugging agent SA-1D.A technology plan is developed to enable the target oilfields to achieve the goal of dewatering and oil-increasing.In this paper,a set of analysis methods of reservoir damage factors and damage degree have been formed,a new acid system with low damage and moderate dissolution has been constructed,and a new type of diversion and water-control material has been developed.The research achievements of this paper have some guiding significance of matching acid system for loose sandstone reservoir matrix acidizing,diversion acidizing technology for heterogeneous reservoirs and dewatering and oil increasing of medium-high water-cut oil wells.