Study On Recovery Mechanism And Technical Stratigies Of Multi-thermal Fluid In Developing Typical Offshore Heavy Oil

China's offshore heavy oil reserves are abundant.Although multi-thermal fluid has been applied successfully to develop offshore heavy oil,oilfield is faced with some problems like low production rate of single well as the development goes.Because the thermal rheological characterisstics of offshore heavy oil and recovery mechanism of multi-thermal fluid play a very important role in the characteristic evaluation,management and development of heavy oil reservoir,therefore it's necessary to evaluate thermal rheological characterisstics of offshore heavy oil,identify recovery mechanism of multi-thermal fluid,optimize technical stratigies,and finally improve thermal recovery system of offshore heavy crude oil.Firstly,taking NB heavy crude oil as an instance,based on Arrhenius equation,activation energy,and phase transition theory,the model and characteristics of heavy oil temperature-visocity is identified;then,characterization methods and evaluation system are formed for rheological model from critical temperature and critical shear rate;and the logarithmic pattern between viscosity and the content of four components is built.Secondly,through multi-thermal fluid experiments,the effect of multi-thermal fluid on reservoir's porosity and permeability is investigated;through different kinds of experiments,the effect of multi-thermal fluid on temperature-visocity characteristics,rheological characteristics and four components is investigated;Moreover,through experiments of water,steam and multi-thermal fluid,development indexes are analyzed in detail and the recovery mechanisms are evaluated from the following aspects such as viscosity reduction by heat,steam distillation,transfer between components and synergistic effect.Finally,based on the parameters of real reservoir and by the help of CMG software,the recovy effect of multi-thermal fluid,steam and hot water is further evaluated from the distribution of temperature field,pressure field,oil saturation field and viscosity field,and the technical stratigies of multi-thermal fluid are determined for injection pattern,composition of multi-thermal fluid and injection rate.The research results of this paper have certain guiding significance for the efficient development of multi-thermal fluid in offshore heavy oil fields.