Research On Chemical Huff-and-puff System For Hekou Heavy Oil

The heavy oil resources in Hekou area are abundant,but due to the edge water and bottom water,as well as incomplete development of interlayer in some blocks,the heat loss in conventional thermal recovery is serious,and some inefficient thermal recovery wells are difficult to maintain due to cost reasons.In this case,it is of great significance to study the chemical huff-and-puff technology and to realize the cold production to Hekou heavy oil.The application of chemical huff-and-puff technology to heavy oil usually requires emulsifying and viscosity reducing ability and oil sweep efficiency of the huff-and-puff liquid,but single surfactant is often difficult to have both good emulsification and strong ability of oil sweep efficiency,and to achieve the purpose,usually surfactants need mixing.This paper synthesized a kind of water-soluble surfactant named nonylphenol polyoxyethylene ether sulfate(NPS-4)which had strong emulsifying ability and good heat resistance and salt tolerance to construct system with high emulsification.This system could make the viscosity-reducing ratio up to 95.2%under the condition of 65?and the volume rate of oil/water of 7:3.Oleic amide propyl betaine(OAB)whose mass fraction was 0.05%was selected as the system with ultra-low interfacial tension.The system with both high emulsification and the ultra-low interfacial tension was constructed by mixing NPS-4 and OAB.The experiments showed that the system“0.15%NPS-4+(0.03~0.05%)OAB”not only had the ultra-low interfacial tension to Hekou heavy oil,but also had viscosity-reducing ratio of more than 96%.Because of the edge water and bottom water and serious heterogeneity of the reservoir in Hekou area,the recovery effect is still not good when chemical huff-and-puff technology is used alone.Therefore,a kind of plugging system is needed using with chemical huff-and-puff system.Based on the modified asphalt powder whose softening point was 55?and true density was 1.09g/cm~3,by studying the suspension stability of the powder,this paper obtained the plugging system”5%modified asphalt powder+0.054%sodium dodecyl benzene sulfonate(SDBS)+0.036%partially hydrolyzed polyacrylamide(HPAM)”which had excellent suspension performance.The plugging system had the water-liberating ratio of 9%in one hour and 25%in two hours.Plugging performance of this system was investigated.The results showed that the plugging system had good performance for injection when the ratio of bore diameter and particle size was over 1.89,and the plugging rate was more than 85%for sand pack models whose permeability was respectively 1224mD,2560mD,4988mD,7135mD.When the ratio of bore diameter and particle size was close to 4:1,the best plugging effect would appear with the plugging rate of 91.8%.The experiments of two parallel sand pack models showed that this plugging system could adjust the heterogeneity of stratum effectively.In order to test the recovery effects of different systems,the physical modelling tests in laboratory have been carried out.The results showed that the increment of indoor recovery rate of the system"0.15%NPS-4"was 12.15%;The increment of indoor recovery rate of the system"0.05%OAB"was 8.23%;The increment of indoor recovery rate of the system"0.15%NPS-4+0.03%OAB"was 16.13%;The increment of indoor recovery rate of the system"0.15%NPS-4+0.05%OAB"was 17.26%.When the chemical huff-and-puff system"0.15%NPS-4+0.05%OAB"and the plugging system”5%modified asphalt powder+0.054%SDBS+0.036%HPAM"were used together,the increment of indoor recovery rate was up to 24.96%,so recommend the chemical huff-and-puff system and the plugging system can be used together when exploiting heavy oil in hekou.