Study On The Effect Of In-situ Combustion In Heavy Oil Of G Reservoir

The heavy oil resource is very rich in China.But the high viscosity of the crude oil cause high mobility ratio of water and oil in heavy oil reservoir,which will cause the problem of high water cut and rapid decline in oil production.There is 0.498 million tons of heavy oil in south of GuDong oil field.The characteristics of this field are high porosity,high permeability and thin oil column.The oil production declines rapidly after the natural depletion production.Now the low formation pressure and high oil saturation and high water cut are the problems in the exploitation of heavy oil reservoir.So based on the present geological condition In-situ combustion with steam preheating is used to enhance oil recovery.According to the characteristics of heavy oil in south of GuDong oil field and the problems in the exploitation of heavy oil reservoir,one-dimensional combustion tube experiment and thermogravimetric experiment and reservoir numerical simulation research are performed.Combustion temperature,hydrogen carbon ratio,fuel consumption and air demand were determined by the one-dimensional combustion tube experiment.The thermogravimetric curve under different heating rate were measured by thermogravimetric experiment.In addition,the reaction activation energy were calculated using the FWO conversion method.The above two experiments can provide the data for numerical simulation and field test.In this paper a one-dimensional numerical model was designed to study the impact of reaction kinetics parameters and ignition temperature on the effect of fire flooding.The history matching process is conducted in three stages.The first stage is the matching of the fuel consumption,by altering the fraction energy of the cracking reaction.The second stage,is the matching of the combustion front velocity and the peak temperatures,by altering the energy and reaction energy of heavy fraction and coke fraction.In the third stage,production fluid rates with the adjustment of the relative permeability curves.This matching data can be used in the numberical simulation.A three-dimensional numerical model is built to study the influence of the gas injection rate,reservoir thickness,oil saturation,crude oil viscosity and heterogeneity on fire flooding.It is found that the gas injection rate is the key factor affecting the effect of the fire flooding.The higher the gas injection rate,the faster the oil recovery rate will be.If the gas injection rate is too high,it will lead to the heat loss and decline in the recovery.In the five-point well pattern,variable speed injection(4000m~3/d、6000m~3/d、8000m~3/d、10000m~3/d、16000m~3/d、22000m~3/d)can get the best development recovery.The in-situ combustion technology is more adaptable for the reservoir thickness,but the thin layer is more suitable for fire flooding.Because in the thick layer gas overriding is obvious,which is not good for the fire flooding.The oil saturation has a great influence on the development of fire flooding.In this paper,oil saturation should be higher than 45%.The in-situ combustion technology is more adaptable for oil viscosity,but it has better effect on the crude oil with lower viscosity.In this paper,the crude oil viscosity between 200~1500mPa·s is better for the fire flooding.Finally,the reservoir heterogeneity has great influence on the fire flooding.And the simulation results show that the positive rhythm layer is more suitable for the fire flooding.The anti-rhythm layer is not suitable for the fire flooding.At present,there is not enough research on fire flooding in thin zone reservoir,therefor the optimization study of well pattern of vertical well and horizontal well for thin zone reservior.The simulation result show that the interleave spot well pattern with 13000m~3/d gas injection rate and 100 meters spacing is better for development.In addition,the staggered line pattern with 16000m~3/d gas injection rate and 140 meters spacing is also better for development.By optimizing the perforation of the vertical wells,it is found that the perforation in the thin layer has little effect on the fire flooding.It is suggested that the middle perforation and the whole perforation can be used.A new kind of horizontal well pattern,with200 meters well spaces and 300 meters horizontal length is better for the development.The gas injection rate is between 16000~20000 m~3/d.