Study on the Percolation Property of Cr~³⁺ Polymer Gel and Profile Controlling Effect in BZ28-2S Oilfield

Bohai BZ28-2S oilfield is characterized by large reservoir thickness,high average permeability,serious heterogeneity,high water salinity and low viscosity of crude oil,and water channeling phenomenon occurred seriously during water flooding,which influenced greatly the oilfield development results.Therefore,it is urgent to take technical measures for profile controlling in order to improve water flooding effect.In view of reservoir characteristics,fluid properties and well pattern of BZ28-2S Oilfield,optimization for Cr³⁺ polymer gel composition has been conducted and study on injection parameters for profile controlling has been carried out through testing viscosity,resistance coefficient,residual resistance coefficient and recovery efficiency.The study results showed that crosslinking reaction might occur between crosslinking agent Cr³⁺ and polymer molecular chains,forming Cr³⁺ polymer gel system,which has intramolecular crosslinking structure,unique percolation property and excellent adaptability to reservoirs under the condition of target reservoir and formation fluids.Compared with polymer solution,Cr³⁺ polymer gel has better effect in profile controlling and flooding effect when the slug size is the same.From economical and technical point of view,it is recommended that the composition of Cr³⁺ polymer gel system should be as follows:C_p is 1 200 mg/L to 1 600 mg/L,m(Pol):m(Cr³⁺)=180:1 to 270:1,and slug size is 0.075 to 0.125 PV,the recovery is expected to increase by 1.6%to 2.5%.On the basis of laboratory experiment results,pilot tests have been carried out in Bohai BZ28-2S Oilfield since December 2013.Currently,Cr³⁺ polymer gel flooding is underway in the pilot.As of May 2013,effect of enhancing oil production has already been obtained during short time.