Research On Profile Control And Oil Displacement For Chenzhuang Heavy Oil Reservoirs

Chenzhuang oilfield,one subordinate oilfield of Shengli,is an ordinary heavy oil reservoir initially exploited by water flooding.Recently,the water cut rose rapidly after water breakthrough and the water flooded residual oil saturation was highly nonuniform due to high permeability channeling widely distributed between wells,resulting from highly viscous crude oil as well as severe heterogeneity.However,after the profile control and drive technology was performed in this reservoir,the results was still unsatisfactory,which is probably because the conventional profile control and drive technology only takes effect for short term application.Therefore,developing a profile-control flooding system applicable to Chenzhuang reservoir is of great importance in order to improve the recovery efficiency in later stage of water flooding.Aiming to meet these challenges such as severe reservoir heterogeneity and high-permeability channeling in Chenzhuang oilfield,an anti-dehydration gel suitable for the formation environment of Chenzhuang oilfield was developed.Low-price Na₂Cr₂O₇-Na₂S₂O₃was selected as the crosslinking agent of this gel,and the gel strength as well as gelling time can be adjusted by the macromolecule organic phosphonic acid salt.The gelling time,gel strength and syneresis rate on Day 30 of this novel gel are 12h,F class and 1.2%respectively.On the basis of the research on profile control system,the alkali/surfactant compound formulation suitable for Chenzhuang heavy oil was studied.Na₂CO₃ was selected as alkali by the alkali/crude oil interfacial tension measurements and alkali/formation brine compatibility tests.Moreover,the surfactants used in addition to Na₂CO₃ were also selected based on alkali/surfactant/crude oil interface tension measurements and alkali/surfactant/formation brine compatibility tests.The result shows that the interfacial tension of alkali/surfactant compound system is the lowest when the ratio of WCBM and SS233?amphoteric surfactant?is 2:3?by mass?,and the alkali/surfactant formulation applicable to Chenzhuang oilfield was consequently determined.Finally,the sand pack flooding experiments for Chenzhuang heavy oil were conducted to evaluate the oil recovery potential by the optimized formulation.The best profile-flooding slug sizes were determined by comparing the incremental oil recovery results of sand pack flooding experiments with various profile control and flooding slug sizes.It is found that the effect of improving oil recovery by profile-flooding combination slug is better than that by either profile control or flooding alone.The highest recovery increment can reach 32.7%when the ratio of profile control slug and the flooding one is 1:1.