Research On Seepage And Reservoir Damage Of Low Permeability And Tight Condensate Gas Reservoir In LFS Field

With the development of petroleum exploration and development in China,more and more low permeability tight condensate gas reservoirs have been discovered.The types of gas reservoirs have both the difficulties of low permeability tight gas reservoirs and condensate gas reservoirs.It has become a hot spot of research at home and abroad,because of the reservoirs’more complex seepage law and oil and gas phase change and high market value.This paper from the low permeability tight gas reservoirs and gas condensate reservoirs in two aspects,using research methods of dynamic analysis,simulation experiment and numerical simulation,analysis the low permeability tight condensate gas reservoirs’ dynamic characteristics and calculates dynamic reserves.It also experimental research on seepage and reservoir damage of low permeability tight reservoirs and gas condensate reservoirs.Based on the dynamic analysis and experimental study,the numerical simulation of the influence of the facies and the permeability of the oil and gas phase,the influence of various percolation mechanisms on the productivity and the effect of fracturing on the reservoir damage are carried out.This paper gets the following conclusions and understanding.(1)The actual analysis of the dynamic characteristics of low permeability tight condensate gas reservoirs shows that the gas-oil ratio is high,the oil pressure is obviously reduced,the output is decreasing faster,and gas oil ratio increases with production time to extend a "hump type" after the occurrence of retrograde condensate in gas reservoir.Decreasing and calculate the dynamic reserves’ results show that the dynamic reserves are 854～5000*104m3,and the dynamic average permeability is 0.06～0.7mD,which is higher than the log interpretation and the rock permeability because of the micro cracks and fracturing effects.(2)The experimental study on permeability and permeability of low permeability tight reservoir shows that the average porosity of target block is 4.92%and the average permeability is 0.16mD,which belongs to the typical low porosity and ultra-low permeability tight gas reservoir.The mobile water saturation in the pore space of the core is limited,and there is a negative correlation between the immobile water saturation and the displacement pressure difference in a certain range.The connectivity between the holes is poor,and the filling methods of core particles are filled cementation and liner cementation.(3)Low penneability tight reservoir stress sensitivity,starting pressure gradient and near wellbore formation fluid lock experiments indicate that permeability stress sensitivity is strong and permeability reduction speed slows down after the highest stress sensitivity damage rate of an average of more than 70%with the increase of net stress.The starting pressure gradient is not obvious.The evaluation of water lock damage degree is high,and with core saturation higher than 80%,the loss of permeability is more than 80%.(4)Condensate gas reservoir seepage and damage related experimental results show that the PVT phase of the target gas reservoir belongs to the low density system with high condensate oil content of condensate gas reservoirs and the dew point pressure is 31.7MPa.The retrograde condensation phenomenon is serious to the equilibrium gas permeability,and the damage can reach about 85%.In the simulation experiment of different failure rate,the condensate oil capacity is strong by the fast failure rate with the percolation channel increased.The failure test with water has the dual effect of water containing complex multiphase flow and small pore channel.(5)Through the study of the facies and oil-gas permeability in the near wellbore,the conclusion is drawn that the pressure in the 30m zone of the near wellbore is very easy to be lower than the dew point pressure,by the phenomenon of reverse condensation.The relative permeability of gas in the near wellbore decreases rapidly,the gas flow capacity decreases with the retrograde condensate,and the near welllbore drops by about 40～50%.(6)To study different seepage mechanism and damage mechanism of production effect show that for fracturing well stress sensitivity,water lock and condensate damage are strong,with the stress sensitivity damage maximum of about 34.95%,the water lock damage followed by about 21.78%and the anti-condensate damage more than about 14.37%.Fracturing operation can effectively reduce the degree of retrograde condensate and water lock damage,but the improvement of stress sensitivity damage is less.