In-situ Combustion Frontal Stability Analysis

In-situ Combustion technology is suitable for the development of different types of reservoirs.It also faces the fingering phenomenon as other EOR processes due to unstable displacement.This will affect the sweep efficiency and reduce the final recovery.At present,the study on the front stability of fire-flooding is limited.Therefore,this thesis aims to study the stability of the fire front by experimental,theoretical and numerical simulation methods for establishing and verifying the front stable criteria.First,an experimental study was performed,including basic core and fluid testing,a combustion cell experiment for determining the kinetic parameters of combustion reactions,and a combustion tube experiment for 1D displacement physical simulation.Next,four factors that may affect the stability of the fire front are analyzed: viscous force,thermal conductivity,permeability reduction by coking and gravity.Four sub-areas(burned area,steam plateau,oil bank,undisturbed area)in the typical fired flooding process were analyzed,and three fronts were determined: combustion front,the front of steam plateau and oil bank.It is also determined that he front of steam plateau is the most unstable front for the highest pressure gradient ratio.On this basis,front stability analysis criteria for fire flooding was established based on the previous research for the front stability of steam flooding,which fully considering the special characteristics and and the upstream/downstream conditions of the steam plateau front in the fire flooding process.Convergence testing ensured the accuracy of numerical simulations.The unstable displacement of the front is captured.Changing the conditions,a large number of numerical simulations and sensitivity analysis were carried out.The key parameters affecting the instability were verified.The reduction of the permeability by coking can`t be the main influencing factor of the front stability.The reliability of the front stability criterion is verified by comparing the numerical simulation results with the previous analysis results.In summary,we have established a criteria for judging the stability of fire-flooding at different conditions.Numerical simulation results show that it has a good predictive power.It can be used as a guiding tool for the implementation of fire-flooding technology to practical production and design.