Research into polymer injection timing for Bohai heavy oil reservoirs

Polymer flooding has been proven to effectively improve oil recovery in the Bohai Oil Field. However, due to high oil viscosity and significant formation heterogeneity, it is necessary to further improve the displacement effectiveness of polymer flooding in heavy oil reservoirs in the service life of offshore platforms. In this paper, the effects of the water/oil mobility ratio in heavy oil reservoirs and the dimensionless oil productivity index on polymer flooding effectiveness were studied utilizing rel- ative permeability curves. The results showed that when the water saturation was less than the value, where the water/oil mobility ratio was equal to 1, polymer flooding could effectively control the increase of fractional water flow, which meant that the upper limit of water/oil ratio suitable for polymer flooding should be the value when the water/oil mobility ratio was equal to 1. Mean while, by injecting a certain volume of water to create water channels in the reservoir, the polymer flooding would be the most effective in improving sweep efficiency, and lower the fractional flow of water to the value corresponding to △Jmax. Considering the service life of the platform and the polymer mobility control capacity, the best polymer injection timing for heavy oil reservoirs was optimized. It has been tested for reservoirs with crude oil viscosity of 123 and 70 mPa s, the optimum polymer flooding effec- tiveness could be obtained when the polymer floods were initiated at the time when the fractional flow of water were 10 % and 25 %, respectively. The injection timing range for polymer flooding was also theoretically analyzed for the Bohai Oil Field utilizing which provided methods for effectiveness. relative permeability curves, improving polymer flooding

A novel profile modification HPF-Co gel satisfied with fractured low permeability reservoirs in high temperature and high salinity

Conformance control and water plugging are a widely used EOR method in mature oilfields.However,majority of conformance control and water plugging agents are unavoidable dehydrated situation in high-temperature and high-salinity low permeability reservoirs.Consequently,a novel conformance control system HPF-Co gel,based on high-temperature stabilizer(CoCl_(2)·H_(2)O,CCH)is developed.The HPF-Co bulk gel has better performances with high temperature(120℃)and high salinity(1×10^(5)mg/L).According to Sydansk coding system,the gel strength of HPF-Co with CCH is increased to code G.The dehydration rate of HPF-Co gel is 32.0%after aging for 150 d at 120℃,showing excellent thermal stability.The rheological properties of HPF gel and HPF-Co gel are also studied.The results show that the storage modulus(G′)of HPF-Co gel is always greater than that of HPF gel.The effect of CCH on the microstructure of the gel is studied.The results show that the HPF-Co gel with CCH has a denser gel network,and the diameter of the three-dimensional network skeleton is 1.5-3.5μm.After 90 d of aging,HPF-Co gel still has a good three-dimensional structure.Infrared spectroscopy results show that CCH forms coordination bonds with N and O atoms in the gel amide group,which can suppress the vibration of cross-linked sites and improve the stability at high temperature.Fractured core plugging test determines the optimized polymer gel injection strategy and injection velocity with HPF-Co bulk gel system,plugging rate exceeding 98%.Moreover,the results of subsequent waterflooding recovery can be improved by 17%.

Polymeric microsphere injection in large pore-size porous media

High water-cut has become a worldwide challenge for oil production.It requires extensive efforts to process and dispose.This entails expanding water handling facilities and incurring high power consumption costs.Polymeric microsphere injection is a cost-effective way to deal with excessive water production from subterranean formations.This study reports a laboratory investigation on polymeric microsphere injection in a large volume to identify its in-depth fluid diversion capacity in a porous media with large pore/particle size ratio.The performance of polymeric microsphere injection was evaluated using etched glass micromodels based on the pore network of a natural carbonate rock,which were treated as water-wet or oil-wet micromodels.Waterflooding was conducted to displace oil at reservoir temperature of 95°C,followed by one pore volume of polymeric microsphere injection.Three polymeric microsphere samples with median particle size of 0.05,0.3,and 20μm were used to investigate the impact of particle size of the polymeric microspheres on incremental oil production capacity.Although the polymeric microspheres were much smaller than the pores,additional oil production was observed.The incremental oil production increased with increasing polymeric microsphere concentration and particle size.As a comparison,polymeric microsphere solutions were injected into oil-wet and water-wet micromodels after waterflooding.It was observed that the oil production in oil-wet micromodel was much higher than that in water-wet micromodel.The wettability of micromodels affected the distribution patterns of the remaining oil after waterflooding and further dominated the performance of the microsphere injection.The study supports the applicability of microsphere injection in oil-wet heterogeneous carbonates.

Study and application of a new blockage remover in polymer injection wells

With the extensive application of polymer flooding technology in offshore oilfields,the plugging in polymer injection wells has become more and more severe,which seriously affects the oil displacement effect and regular production of oilfields.In this paper,a new kind of blockage remover has been developed and evaluated by rheological behavior experiments,dissolution experiments and core flooding experiments.The results reveal that this new blockage remover can effectively reduce the viscosity of polymer and completely degrade the reservoir blockage with low corrosion rate.It is beneficial to long-term production of oil wells in offshore oilfield.Results of core flooding experiments show that this new blockage remover can relieve polymer damage and improve permeability.The agent has been applied in LD10-1 oilfield in 2016,the daily injection rate increased significantly after stimulation.