Experimental Study On Nitrogen Foam Flooding In Low Permeability Reservoir

X reservoir in Xinjiang oilfield is a low porosity,low permeability and serious heterogeneity reservoir.The contradiction among the reservoir layers is very significant in the process of water flooding.Injected water channels in high permeability layer which leads to the water cut rising quickly,and low permeability layer is poorly used,the remaining oil of the reservoir is large.This study focuses on nitrogen foam flooding for X reservoir to further enhanced oil recovery.In this study,the nitrogen foam agent was developed.Then,the liquid phase viscosity,the adsorption performance of the foaming agent,the pressure and the influence of crude oil on the foam stability was investigated.The displacement efficiency characteristics of nitrogen foams in low permeability homogeneous cores,parallel heterogeneous cores and three parallel heterogeneous cores were studied.Through the above research,the main results and understandings are as follows:(1)0.25%Y1 foaming agent still remained excellent foaming and stability ability after aging 90 days under reservoir temperature(73?)and salinity(TDS 24818.5 mg/L),with the foaming volume of 554mL and the half-life of 162s.Polymer 4 could effectively prolong the half-life of the foam solution,the foam half-life prolonged with the increase of the polymer concentration and approximately satisfied the linear relationship.0.25%Y1+0.2%P4 foaming agent remained good stability after aging 90days with the foam half-life of 946s.(2)For the enhanced foaming agent formed by the addition of polymer and the same surfactant,the main factors that affect the stability of the foam are the viscosity,not the interfacial tension and the surface tension.High pressure helps to improve the stability of the foam.The crude oil of X reservoirs has no significant effect on the foaming performance of ordinary foam and enhanced foam,the addition of polymers to the foaming agent is helpful to improve the relative stability of oil-containing foam.(3)The homogeneous core displacement experiment indicated that gas-liquid ratio,foam injection velocity,foam injection PV and foam injection time had a great effect on the foam flooding:?The gas-liquid ratio and the foam injection velocity had a reasonable value so that the nitrogen foam flooding obtained the best oil displacement efficiency in the process of foam flooding and subsequent water flooding.?The oil displacement efficiency of nitrogen foam flooding increased with the increase of foam injection amount,when the foam injection amount was more than 0.5PV,the oil displacement efficiency increased slowly.?In the experimental range(the water cut range from 71.43%to 98.32%),the timing of injection nitrogen foam was in advance to improve oil displacement efficiency.(4)With the water flooding and nitrogen foam flooding speed of 5.94m/d,through parallel core displacement experiments could be obtained:?water flooding could start low permeability core of the permeability contrast of 5.22,and could not start low permeability core of the permeability contrast of 7.20.?For the parallel core with permeability contrast of 10.67,ordinary foam could establish excellent flow control ability to reduce diversion rate of the high permeability core and increase diversion rate of the low permeability core,it could effectively increase the oil displacement efficiency of the high permeability core and low permeability core.However,it could not start the low permeability core with permeability contrast of 15.46.?The enhanced nitrogen foam could effectively start the low permeability core with permeability contrast of 15.68.?With the time of injection foam in advance,ordinary nitrogen foam on the use of low permeability core gradually weakened for permeability contrast of about 10,the low permeability core could not be used when the foam injection time for the water cut of 76.69%.(5)For the three-parallel heterogeneous core with permeability variation coefficient of 0.28 and 0.72,water flooding could only use the low permeability core of the former,and the nitrogen foam could effectively use the low permeability core of the latter,and oil displacement efficiency of nitrogen foam flooding on the three-parallel heterogeneous core with large permeability variation coefficient was poor.The understanding of nitrogen foam in low permeability and serious heterogeneous reservoirs would be beneficial to enrich the application range of nitrogen foam flooding.At the same time,it is a great practical significance for the nitrogen foam flooding to enhanced oil recovery.