Copy ri ght 7896 , Stee ri ng Committee of the Euro pean IOR -Symposium. This paper was presented at the 8th . Eu ropean IOR -Symposium in V ierma, Austr ia, May 15 -17, 1995 Thi s paper was eelected for presentation by the Stee ri ng Committee , follow ing review of information contained i n en abstract subm itted by the authorlsl . The paper, as presented hes not been reviewed by the Stee ring Comm itt ee . AbstractThe drainage of oil under gravitational forces has been an important mechanism in the production of many oil fields . In order to extend the economic implementation of gas injection into more marginal fields, a reduction in the uncertainties associated with gravity drainage is required. This paper describes a series of three tertiary, nitrogen experiments which investigated the effect of permeability on gravity drainage . The experiments ware conducted at low pressure using long, vertical, water-wet sandstone sores and decane in the presence of connate brine .The residual oil saturation following 62 days of nitrogen injection in a 0 .37 µmz core was 0 .26. The residual oil saturation following 53 days of nitrogen injection in a 1 . 5 µm2 Gore was 0 . 10.The residual oil saturation following 63 days of nitrogen injection in a 2 .0 µmz Gore was 0 . 13 . The variation of the oil and brine saturations ware determined as a function of space and time for each experiment using a radioactiva tracer technique . This independent measurement of both o il an d brine in-site saturations is a new development for the literature and enables vore a rtefacts to be identified and relativa permeabilities to be derived .Detailel analysis of the 2 µm2 experiment showed that the o il relativa permeability was independent of position and was only a function of oil saturation . The relativa permeabilities are characterised by a zero asymptotic residual oil saturation and a Corey exponent of approximately four , which is higher than the value of three proposed from theoretical models of film drainage . A numerical simulation of this experiment gave a good match to the production and in-site saturation data. This paper presents the determination of oil and brine relativa perineabilities under a flow regime which is representative of gravity drainage during gas injection . The method outlined thus gives added confidence when assessing field development options .
The drainage of oil under gravitational forces has been an important mechanism in the production of many oil fields. In order to extend the economic implementation of gas injection into more marginal fields, a reduction in the uncertainties associated with gravity drainage is required. This paper describes a series of three tertiary, nitrogen experiments which investigated the effect of permeability on gravity drainage. The experiments were conducted at low pressure using long, vertical, water-wet sandstone cores and decane in the presence of connate brine. The residual oil saturation following 62 days of nitrogen injection in a 0.37 mu m 2 core was 0.26, following 53 days of nitrogen injection in a 1.5 /mu m 2 core was 0.10 and following 63 days of nitrogen injection in a 2.0 /mu m 2 core was 0.10. The variation of the oil and brine saturations were determined as a function of space and time for each experiment using a radioactive tracer technique. This independent measurement of both oil and brine in situ saturations is a new development and enables core artefacts to be identified and relative permeabilities to be derived. Detailed analysis of the 2 mu m 2 experiment showed that the oil relative permeability was independent of position and was only a function of oil saturation. The relative permeabilities are characterized by a zero asymptotic residual oil saturation and a Corey exponent of approximately four, which is higher than the value of three proposed from theoretical models of film drainage. A numerical simulation of this experiment gave a good match to the production and in situ saturation data. Determination of oil and brine relative permeabilities under a flow regime are presented which are representative of gravity drainage during gas injection. The method outlined gives added confidence when assessing field development options.
A determination of oil relative permeability data during secondary and tertiary, gravity stable, nitrogen injection experiments is described. Four experiments were conducted at high and low pressure using vertical Clashach sandstone cores and a dead oil in the presence of connate brine. The spatial distributions of oil throughout the cores were determined using a radioactive tracer technique and these in-situ saturation measurements were used to determine the oil relative permeability. The results of two new experiments are presented. A high pressure, secondary, gravity stable, nitrogen injection was conducted in a 1790 mm core with a connate water saturation of 0.25. The residual oil saturation following 12 days of gas flooding was 0.19. A low pressure, tertiary, gravity stable, nitrogen injection was conducted in a 841 mm core with a connate water saturation of 0.19. A residual oil saturation to water flooding of 0.51 was reduced to 0.09 after 37 days of drainage. The rate of change of oil relative permeabilities with respect to oil saturation was larger in the secondary, gravity stable, nitrogen injection than in the tertiary injection. The predicted residual oil saturation to gas corresponding to an infinite drainage time appears to be finite for secondary gas injection and zero for tertiary gas injection. The permeability data is consistent with a theoretical model of film drainage which predicts a Corey Exponent of three.
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