Research On Deep Profile Control And Flooding Of Redevelopment Phase In E31 Reservoir

GS-E31 reservoir in West China has ultra-high temperature 126OC,and ultra-high salinity 17×104mg/L.The average porosity of the reservoir is 14.34%and the permeability is 51.3mD.It is highly heterogeneous,developed with flowing channels.After the first development and production for thirty years,GS-E31 reservoir is into the rapid decline in production stage,the economic benefits is deteriorated,and composite water cut gets 84.6%.Currently in the secondary development stage,through adjust the development of program and water control enhanced oil technology,the effect is not significant and water flooding recovery rate is low.In this paper,according to the characteristics of E31 reservoir with ultra-high temperature and ultra-high salinity.With high water cut and the scattered distribution of residual oil in secondary development stage.Proposes through the preparation of temperature resistance and brine resistance cross-linked polymer gel and the optimization of polymer microspheres,to achieve substantial increase in recovery.On the one hand,due to the strong heterogeneity of the reservoir,adopt the preparation of gel to seal high permeability layer and large holes,and to adjust the water injection profile.On the other hand,the residual oil distribution is scattered or in the low permeability layer and the micro-pore throat which are not affected by the injection of water.The polymer microspheres is carried out in deep flooding to improve the efficiency,thereby increasing the recovery of water flooding.Because of the conventional flooding agent had shortcomings in field test like poor thermal stability and dehydration in high temperature and high salinity environment.On the basis of sufficient investigation,the polymer FOPAM-4650S and phenolic crosslinking agent F1 were screened out.The experiments were carried out cross-linked polymer gel system suitable for the E31 reservoir.The optimized formulation of the cross-linked polymer gel can be summarized as 2000 mg/L of polymer FOPAM-4650S concentration,180 mg/L of crosslinking agent F1 concentration and 100 mg/L of oxygen scavenger concentration.The cross-linked polymer gel has good temperature resistance,brine resistance and long-tern stability.After placed for 60d it still maintain good stability,can adapt to the reservoir of high temperature and high salinity environment.Based on the low permeability of the reservoir and the size of pore throat at the micron level,the polymer WQ-? microspheres were optimized which is matching with the pore size of E31 reservoir.Placed the WQ-? microspheres at 126 ? and expanded in fresh water for 14 days and 28 days,the expansion ratio increased from 4.10 to 5.84.After 14 days expanded in formation water,the swelling ratio was still 6.22.Indicating that this polymer microspheres had good temperature resistance,brine resistance,but also has good suspension dispersion and viscoelasticity.The results of core flow experiments show that both the cross-linked polymer gel and the polymer microspheres have good injection capacity,and the concentration of the injected microspheres is 2000mg/L.Considering the size of different PV slugs,when the size of the cross-linked polymer gel is 0.3PV and the size of the microspheres is 0.1 PV,the recovery rate was the largest.Enhanced oil recovery is 23.9%.In the plugging experiment of composite profile control system,the plugging rate can reach more than 94.9%and the breakthrough pressure gradient is above 4.224MPa/m,which shows that this system has good plugging performance and flushing resistance.In the experiment of improving ratio of water entry profile in parallel,the improving factor of water entry profile is above 73.5%.The research results concluded in this paper can offer theoretical assistance for guiding recovery enhancement for the E31 reservoir who in the stage of secondary development.And provide useful experiences for similar reservoirs in terms of waterflooding and enhanced oil recovery.