In-situ Combustion Mechanism And Optimization Of Operation Parameters For Multilayer Heavy Oil Reservoir

During the development of fire flood in multi-layer heavy oil reservoir,the contradictions are prominent in the plane and vertical directions.The injected air is easy to march forward along one-way and single layer,and it is difficult to understand the fire-line sweep law.Meanwhile,due to the high temperature effect and coke deposition,the physical properties and production capacity of different layers change significantly in different development stages and combustion zones.However,current numerical simulation models did not consider the changes of reservoir physical properties in the process of fire flood.Therefore,revealing multi-layer fire line sweep law,establishing multi-layer numerical simulation model considering variable reservoir permeability,and finally predicting the production capacity of different layers in different development stages of multi-layer fire flood,can provide more frontier technical support for the efficient development of multi-layer heavy oil reservoirs.Key results are obtained as follows:(1)Based on the field dynamic data,the main control factors of multi-layer fire line sweep are analyzed.According to the characteristics of long well section,multi-layer reservoir and strong plane heterogeneity,the prediction approach of multi-layer fire line position is established on the basis of material balance method,combining with production dynamics and gas profile monitoring.Taking this method as the theoretical basis of fire line control in field,we analyze the application effects of shut-in gas control,gas channeling plugging and stratified gas injection in injectors.(2)For the multi-layer heavy oil reservoirs with general gas injection,the parameters along vertical wellbore are characterized by taking conventional single-pipe air injection as an example.Aiming at the stratified gas injection,a mathematical model is established for predicting the parameters along the concentric double tubes in vertical wellbore,and a new method for calculating the air pressure distribution in annular space is put forward.The prediction of gas absorption capacity and fluid physical parameters distribution of general/stratified gas injection can be achieved by establishing the model for calculating wellbore parameters of multi-layer fire flood gas injection.(3)The mechanism of the variation of physical properties in fire flood reservoir are analyzed.By considering the effect of high temperature and coke deposition on reservoir physical properties in different development stages and combustion zones,the variable permeability fire drive mathematical model is established.Then,we simulate the influence of reservoir physical properties on multi-layer fire flood,and investigate the sensitivity of geological factors and injection-production parameters.(4)The variable permeability model is applied to evaluate the fire flood productivity of multi-layer heavy oil reservoirs.The geological model of D block is established first.Then we calculate the chemical reaction parameters and built the chemical reaction model using the experimental data of TGA/DSC.After that,the accuracy and advantages of variable permeability model are verified through historical matching of typical well groups.The optimization of multi-layer fire flood gas injection mode and injection-production parameters in Block D are obtained.Finally,the suggestions of multi-layer fire drive control are given.This study has a theoretical guiding significance for the efficient development of in-situ combustion reservoirs in multi-layer heavy oil reservoirs.