Screening And Assessing Of Viscosity Reducer For Extra-heavy Oil

With the increasing demand for oil resources in the world and the reduction of conventional reservoir resources which are easy to be exploited.The unconventional reservoir resources including heavy oil become more and more important.High viscosity and poor fluidity of heavy oil are the main factors restricting heavy oil recovery.In this paper,based on the investigation of viscosity reduction technology and mechanism of a large number of heavy oil,the ultra-heavy oil YS7 well in western China was taken as the research object,and the characteristics of its viscosity,components and heteroatoms containing N,S and O were analyzed in the detail.Based on the combination of biosurfactants and chemical surfactants,the optimal viscosity reducing system for heavy oil in YS7 well was compounded,and the effects of heavy oil emulsification,oil washing and core simulated oil displacement experiments were carried out to evaluate the effects of complex viscosity reducing system.The crude oil viscosity of heavy oil in YS7 well reaches 38124 m Pa·s at formation temperature,which belongs to ultra-heavy oil.The heavy oil colloidal asphaltene in well YS7 has a high content of colloidal asphaltenes and a low content of light hydrocarbons（1.24%）.The colloidal and the asphaltene contain a large number of S,O,N polar compounds,these polar compounds intermolecular force which is strong,and the formation of large cement is a major factor of high viscosity heavy oil.The surfactant-producing strain LZ3-2 strain which belongs Pseudomons spp.The best fermentation conditions of the strain are:（g/L）sucrose 20g,Sodium glutamate 7g,KH₂PO₄6.8g,KC l0.5g,Mg SO₄0.2g,Fe SO₄11 mg,Mn SO₄0.5 mg,Zn SO₄0.09,Cu SO₄0.07 g,Na OH1.4g.Three systems of CDJN,CDJN1 and CDJN2 for ultra-heavy oil YS7 were obtained by compounding and the compounding system was mainly composed of biological ampholytic surfactant ASY,anionic surfactant CDA6,chemically active molecular CDXYL,biologically active molecular CDSWM1 and LZ3-2 fermentation broth.The three composite systems can keep the viscosity of heavy oil below150m Pa·s at formation temperature（60℃）,among which CDJN2 has the best effect to reduce the viscosity of heavy oil to below 70m Pa·s in YS7 well.The ultra-heavy oil viscosity reducer system of YS7 well can be effectively enhanced the oil recovery rate in the core displacement simulation experiments,among which the viscosity reducer system CDJN2 can enhance the recovery rate of heavy oil about 30%,with good emulsification and stripping capacity of heavy oil,which can be used in field trials.