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Application of NMR imaging to steam foam flooding in porous media
Magnetic
Resonance
Imaging,
Vol. 14. Nos. 718, pp. 949-950, 1996 Copyright 0 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725X/96 $15.00 + .oO
PI1 SO730-725X(96)00191-7
ELSEVIER
0 Short Communication APPLICATION
OF NMR IMAGING TO STEAM FLOODING IN POROUS MEDIA
CHEN QUAN, * WANG WEIMIN, * AND CAI XIANCHUN
FOAM
t
*Institute of Porous Flow, CNPC & Academic Sinica, 44, Langfang, Hebei, 102801, China, ?Institute of Drilling Well & Oil Production, Liaohe Petroleum Exploration Bureau Applications of NMR imaging to examine the fluid distribution of steam foam flooding as a function of concentration and volume of surfactant solution, and residual oil saturation are described. The features examined include sweep efficiency, oil recovery, resistance factor, apparent viscosity, steam quality, and foam stability. The results illustrate that the injection procedure and residual oil saturation have a significant influence on steam foam flooding. Copyright 0 1996 Elsevier Science Inc. Keywords:
NMR imaging; Steam foam flooding; Porous media; Sweep efficiency.
field was 4.7 Tesla. The diameter of the probe head was 7 cm. Cylindrical sand packed cores (length 8.50 cm, diameter 3.20 cm, porosity 0.39, permeability 7 pm’) were evacuated by pump for 8 h, then saturated by formation water that contained 500 ppm MnC12. The cores were then flooded with heavy oil to leave irreducible water, steam flooded to leave residual oil and then steam foam flooded. Steam at 290°C was produced by a steam generator. Pressure was measured by a pressure transducer. Using 2DFI and CSSI sequences, the main parameters for imaging were TR = 500 ms, TE = 3.56 ms, matrix size 128’, time of imaging 2 min. 33 s.
INTRODUCTION Heavy oil is usually driven by steam in reservoirs, but the large difference of density and viscosity between heavy oil and steam often causes steam gravity override and channelling along a high permeable layer of the reservoir, so that the sweep efficiency of steam flooding is very low. The concept of using foam to reduce gas mobility was initially patented by Bond and Holbrook in 1958.’ The Properties of flowing foam in porous media containing oil are very complex.2 Using the NMR imaging technique, this paper studies the mechanisms of heavy oil displacement by steam foam in porous media.
RESULTS MATERIALS
AND METHODS
AND DISCUSSION
The behavior of steam foam was investigated with different types and different concentration of surfactant under different residual oil saturation. The strength of the in situ-generated foam, expressed by the apparent viscosity is significantly affected by the injection procedure, slug size, surfactant concentration, and steam
The spatial distribution of fluid saturation in a core was obtained by an NMR imaging scanner during the process of displacement. Experiments were carried out on a BRUKER 47/40 NMR imaging/spectroscopy system. The strength of the superconductive magnetic Address correspondence to Chen Quan, Institute of Porous Flow, CNPC & Academic Sinica, 44, Langfang, Hebei,
102801, China.
949
Magnetic Resonance Imaging 0 Volume 14, Numbers 7/8, 1996
950
quality. Experimental results imply that savings in the total mass of surfactant needed for a steam foam flood may be possible by an alternative surfactant steam procedure that utilizes a sufficiently large slug volume; that is, if the slug volume is above some minimum, then a dilute concentration of surfactant may give acceptable foam generation. However, a high concentration of surfactant in a small slug volume is ineffective. The Resistance factor is used to indicate the incremental resistance properties of flowing foam. The residual oil saturation after steam flooding has a significant influence on the resistance factor of steam foam flooding. Systems including more residual oil after steam flooding result in a lower resistance factor compared to systems with less residual oil in the core, because spreading of the oil on foam bulbs or lamellas decreases the stability of the foam. Oil spreading may cause film thinning below a critical limit for mechanical stability, and the lamella breaks. Special image processing software was used to calculate the distribution of fluid and the sweep efficiency during the process of displacement. The distribution of primary oil and irreducible water in the core is shown in Fig. la. The distribution of oil and water after steam flooding is shown in Fig. lb. The steam mainly sweeps the high permeability layer of the core, but the low permeability layer is swept only slightly. The distribution of oil and water after steam foam flooding is shown in Fig. lc. Steam foam flooding can obviously increase sweep efficiency and oil recovery.
a
b
CONCLUSIONS Steam foam flooding results in a large resistance factor and apparent viscosity by the Jiamin effect, reduces mobility of steam, improves sweep efficiency, and oil recovery. A higher residual oil saturation after steam flooding results in a lower resistance factor during steam foam flooding. An alternative surfactant steam procedure that utilizes a large slug volume and low concentration of surfactant is more effective.
REFERENCES 1. Bond, D.C.; Holbrook,
O.C. Gas Drive Oil Recovery Pro-
cess, U.S. Patent 2,866,507 (1958). 2. Kristiansen, T.S.; Holt, T. Properties of Flowing Foam in Porous Media Containing Oil SPE/DOE 24182.
Fig. 1. NMR images of distribution of oil and water in the core. (a) Primary oil content. (b) After steam flooding. (c) After steam foam flooding.
Resonance
Imaging,
Vol. 14. Nos. 718, pp. 949-950, 1996 Copyright 0 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0730-725X/96 $15.00 + .oO
PI1 SO730-725X(96)00191-7
ELSEVIER
0 Short Communication APPLICATION
OF NMR IMAGING TO STEAM FLOODING IN POROUS MEDIA
CHEN QUAN, * WANG WEIMIN, * AND CAI XIANCHUN
FOAM
t
*Institute of Porous Flow, CNPC & Academic Sinica, 44, Langfang, Hebei, 102801, China, ?Institute of Drilling Well & Oil Production, Liaohe Petroleum Exploration Bureau Applications of NMR imaging to examine the fluid distribution of steam foam flooding as a function of concentration and volume of surfactant solution, and residual oil saturation are described. The features examined include sweep efficiency, oil recovery, resistance factor, apparent viscosity, steam quality, and foam stability. The results illustrate that the injection procedure and residual oil saturation have a significant influence on steam foam flooding. Copyright 0 1996 Elsevier Science Inc. Keywords:
NMR imaging; Steam foam flooding; Porous media; Sweep efficiency.
field was 4.7 Tesla. The diameter of the probe head was 7 cm. Cylindrical sand packed cores (length 8.50 cm, diameter 3.20 cm, porosity 0.39, permeability 7 pm’) were evacuated by pump for 8 h, then saturated by formation water that contained 500 ppm MnC12. The cores were then flooded with heavy oil to leave irreducible water, steam flooded to leave residual oil and then steam foam flooded. Steam at 290°C was produced by a steam generator. Pressure was measured by a pressure transducer. Using 2DFI and CSSI sequences, the main parameters for imaging were TR = 500 ms, TE = 3.56 ms, matrix size 128’, time of imaging 2 min. 33 s.
INTRODUCTION Heavy oil is usually driven by steam in reservoirs, but the large difference of density and viscosity between heavy oil and steam often causes steam gravity override and channelling along a high permeable layer of the reservoir, so that the sweep efficiency of steam flooding is very low. The concept of using foam to reduce gas mobility was initially patented by Bond and Holbrook in 1958.’ The Properties of flowing foam in porous media containing oil are very complex.2 Using the NMR imaging technique, this paper studies the mechanisms of heavy oil displacement by steam foam in porous media.
RESULTS MATERIALS
AND METHODS
AND DISCUSSION
The behavior of steam foam was investigated with different types and different concentration of surfactant under different residual oil saturation. The strength of the in situ-generated foam, expressed by the apparent viscosity is significantly affected by the injection procedure, slug size, surfactant concentration, and steam
The spatial distribution of fluid saturation in a core was obtained by an NMR imaging scanner during the process of displacement. Experiments were carried out on a BRUKER 47/40 NMR imaging/spectroscopy system. The strength of the superconductive magnetic Address correspondence to Chen Quan, Institute of Porous Flow, CNPC & Academic Sinica, 44, Langfang, Hebei,
102801, China.
949
Magnetic Resonance Imaging 0 Volume 14, Numbers 7/8, 1996
950
quality. Experimental results imply that savings in the total mass of surfactant needed for a steam foam flood may be possible by an alternative surfactant steam procedure that utilizes a sufficiently large slug volume; that is, if the slug volume is above some minimum, then a dilute concentration of surfactant may give acceptable foam generation. However, a high concentration of surfactant in a small slug volume is ineffective. The Resistance factor is used to indicate the incremental resistance properties of flowing foam. The residual oil saturation after steam flooding has a significant influence on the resistance factor of steam foam flooding. Systems including more residual oil after steam flooding result in a lower resistance factor compared to systems with less residual oil in the core, because spreading of the oil on foam bulbs or lamellas decreases the stability of the foam. Oil spreading may cause film thinning below a critical limit for mechanical stability, and the lamella breaks. Special image processing software was used to calculate the distribution of fluid and the sweep efficiency during the process of displacement. The distribution of primary oil and irreducible water in the core is shown in Fig. la. The distribution of oil and water after steam flooding is shown in Fig. lb. The steam mainly sweeps the high permeability layer of the core, but the low permeability layer is swept only slightly. The distribution of oil and water after steam foam flooding is shown in Fig. lc. Steam foam flooding can obviously increase sweep efficiency and oil recovery.
a
b
CONCLUSIONS Steam foam flooding results in a large resistance factor and apparent viscosity by the Jiamin effect, reduces mobility of steam, improves sweep efficiency, and oil recovery. A higher residual oil saturation after steam flooding results in a lower resistance factor during steam foam flooding. An alternative surfactant steam procedure that utilizes a large slug volume and low concentration of surfactant is more effective.
REFERENCES 1. Bond, D.C.; Holbrook,
O.C. Gas Drive Oil Recovery Pro-
cess, U.S. Patent 2,866,507 (1958). 2. Kristiansen, T.S.; Holt, T. Properties of Flowing Foam in Porous Media Containing Oil SPE/DOE 24182.
Fig. 1. NMR images of distribution of oil and water in the core. (a) Primary oil content. (b) After steam flooding. (c) After steam foam flooding.