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Flow Characteristics of Heavy Oilthrough Porous MediaH. Liu

a, J. Wang

a, Y. Xie

b, D. Ma

b& X. Shi

b

a

MOE Key Laboratory of Petroleum Engineering in China Universityof Petroleum , Beijing , ChinabHenan Oil Field Company, SINOPEC , Henan , Nanyang , China

Published online: 02 Jan 2012.

To cite this article:H. Liu , J. Wang , Y. Xie , D. Ma & X. Shi (2011) Flow Characteristics of Heavy Oilthrough Porous Media, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 34:4,

347-359, DOI: 10.1080/15567036.2011.609868

To link to this article: http://dx.doi.org/10.1080/15567036.2011.609868

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Energy Sources, Part A, 34:347359, 2012

Copyright Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/15567036.2011.609868

Flow Characteristics of Heavy Oilthrough Porous Media

H. LIU,1 J. WANG,1 Y. XIE,2 D. MA,2 and X. SHI2

1MOE Key Laboratory of Petroleum Engineering in China University of

Petroleum, Beijing, China2Henan Oil Field Company, SINOPEC, Henan, Nanyang, China

Abstract Performance of flowing through a capillary and porous media for differentkinds of heavy oil at different temperatures have been studied by experiments in this

article. It shows that the heavy oil containing asphaltene-colloids displays yield-stressrheology (Bingham fluids). The displacing pressure difference increases linearly with

the increase of the flow rate. However, the start flowing pressure is different fordifferent heavy oil samples at different temperatures. The higher the temperature is,

the lower pressure the heavy oil needs to flow; and when the temperature is highenough, the start flowing pressure equals zero. The minimum temperature at which

the start flowing pressure equals zero is called converting temperature. Also, the moreviscous the heavy oil is, the higher the converting temperature will be. An exponential

relationship of yield stress and temperatures has been obtained for different kinds of

heavy oils by the experiments of heavy oil flowing through a capillary. A logarithmicrelationship of converting temperatures and the dead oil mobility at 50C has beenobtained for heavy oil through different porous media. When a temperature is lower

than the converting temperature, the start flowing pressure gradient decreases as alog tendency with the increase of temperature when different heavy oils are flowing

through different porous media. For the existence of the start flowing pressure gradient,the heavy oil production rate is different from that for the Newton fluid and it is

adverse to the development of heavy oil reservoirs. The test results are favorable tochoose the reasonable temperature for heavy oil transportation running in a pipe

or well bore and also determine the temperature limitation for different productionrates for a specific well sample. It is also important for improving the development

effect efficiently.

Keywords converting temperature, flow characteristics, heavy oil, porous media,start flowing pressure gradient

1. Introduction

Oil is the most important energy now. Heavy oil resources are very abundant in the

world. The geologic reserves are much higher than conventional crude oil. A major

flow assurance challenge in the near future is the production and transport of heavy

oils (Henaut et al., 2003). Heavy oil has been repeatedly verified as suspensions of

Address correspondence to Dr. Jing Wang, MOE Key Laboratory of Petroleum Engineering,China University of Petroleum, Beijing 102249, China. E-mail: [email protected]

347


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348 H. Liu et al.

asphaltene colloids stabilized by resins (Yen and Chilingarian, 1994; Mullins and Sheu,

1998; Wong and Yen, 2000), which leads to the heavy oil representing some unusual

flowing behaviors through pipes and porous media (Steinborn and Flock, 1983; Hasan

et al., 2010; Luo and Gu, 2009). Commonly, heavy oil is a kind of non-Newtonian

fluid and belongs to Bingham fluid. This opinion has been proved by many experimental

evidences (Bedrikovetsky, 1995; Barenblatt et al., 1990; Evdokimov et al., 2001). But it

depends on its ambient temperature. It could be Newtonian fluid at a higher temperature

(Wang et al., 2009). Generally, there exists a temperature limitation that the beginning

flow pressure gradient equals zero because of its sensitivity to temperature, which is

called the converting temperature. Undoubtedly, converting temperature is important for

heavy oil transportation performing through pipes, and it will play an important role

in selecting injection fluids temperature through porous media, or in determining well

deliverability at a specific formation temperature (Liu and Zhang, 1999; Liu and Wu,

1996). So, formation temperature will be held above the temperature limitation in order

to obtain the desirable mobility in oil production. Heavy oil in different reservoirs has

different converting temperatures (Martn-Alfonso et al., 2006). However, the formationtemperature is not always higher than its converting temperature and the start flowing

pressure exists. In order to obtain the desirable production rate, some reasonable measures

must be adopted, such as heating the reservoir or increasing the producing pressure

difference. Therefore, it is very necessary to measure the converting temperature for

different heavy oils in different reservoirs or ascertain the start flowing pressure at

a specific temperature to decide the reasonable injection pressure, which will supply

valuable guidances to field application and improve the development effect of heavy oil

reservoirs.

2. Tests of Heavy Oil Flowing through Capillaryand Porous Media

The heavy oil with comparatively high concentrations of asphaltenes-colloids stabilized

by resins is from the Jinglou reservoir blocks of Henan Oilfield in China. The asphaltenes-

colloids concentrations of No. 1, No. 2, and No. 3 are 17.6, 21.4, and 23.8 wt%, respec-

tively, and the viscosity shows a linear rule with the same slope at ASTM coordinate.

2.1. Test of Heavy Oil Flowing through Capillary

Heavy oil flowing rate and displacement pressure difference can be measured for differenttemperatures through a capillary. The length of the capillary is 3 m and the diameter is

0.0017 m. In order to heat the heavy oil adequately and stabilize the temperature, the

devices and heavy oil samples are heated for about 5 h in the thermotank first at each

experimental temperature. The pressure difference from the capillary inlet to outlet and

heavy oil flowing rate should be recorded until the displacing process is in a steady state.

Three oil samples have been tested at different temperatures and the testing results are

shown in Figure 1.

It shows that the displacement pressure difference increases linearly as heavy oil

flowing rate increases at any specified temperature. There is a temperature limitation

below, in which the heavy oil cant flow when a little displacement pressure difference is

available. The reason is that the three-dimensional network structure influenced deeply by

the oil viscosity will stop the heavy oil flowing and the oil viscosity is mainly decided by


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Flow Characteristics of Heavy Oil 349

(a)

(b)

Figure 1. Heavy oil flowing test through a capillary: (a) heavy oil No. 1, (b) heavy oil No. 2, and

(c) heavy oil No. 3. (continued)

the content of wax, colloid, and asphalt in heavy oil. The more content the wax, colloid,

and asphalt contains, the stronger the network structure is. So, the additional force and

yield stress are needed to break it. At the same time, the strength of the network structure

will sharply decrease as the temperature increases because of the dissolution of wax,

colloid, and asphalt on heating.

The heavy oil can be regarded as incompressible fluid and laminar flow in the

capillary (Khashan and Al-Nimr, 2005; Alkam et al., 1998); and the tip effect and inertia

force could be neglected for the long pipe and stable flow. Therefore, the viscous force

equals the pressure differential from the inlet to the outlet.


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350 H. Liu et al.

(c)

Figure 1. (Continued).

Thus, there is a force balance as follows:

p1 r2 p2 r2 D 2rL: (1)

So, the shearing stress on the capillary wall is

jrDRD .p1 p2/R

2L : (2)

Then, the additional pressure gradient that heavy oil starts to flow is

pG

L D 2B jrDR

R : (3)

Thus, the yield stress can be obtained from tested data for different oil samples,

and the converting temperatures of different heavy oils are also obtained. The converting

temperature is 46.91

C for the heavy oil No. 1, 54.33

C for the heavy oil No. 2 and63.08C for the heavy oil No. 3. The start flowing pressure gradient and yield stress

below the converting temperature are listed in Table 1.

2.2. Test of Heavy Oil Flowing through Porous Media

Heavy oil flowing through porous media has also been performed. The length of the sand

pack is 0.6 m and the diameter is 0.0038 m. It is filled with sand grains of different meshes

to get different permeable media, and some glass beads are added to simulate surface

wettability of the reservoir rock, which is aimed to make the experimental condition be

close to the reservoir condition. The sand grains of 20 meshes are used to compact the

high permeable tube with the permeability of 6.73 m2 and porosity of 0.35; 80 meshes

are compacted to a 1.6 m2 permeable tube and porosity is 0.32; and a 2.55 m2


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Table 1

Heavy oil properties below the converting temperature

No. 1 Temperature, C 10 20 30 40 45

Start flowing pressure gradient, kPa/m 54.12 28.13 14.00 4.00 2.1

Yield stress, Pa 23.00 11.96 5.95 1.7 0.89



Yield stress, Pa 54.89 33.15 19.69 8.63 3.60



Yield stress, Pa 212.00 136.41 81.26 40.38 9.35

permeable tube was filled with 40 and 80 meshes sand grains combination with theporosity of 0.34. Figure 2 shows the test results for heavy oil No. 2 through different

kinds of permeable porous media.

It has also been shown that there also exists a converting temperature for heavy

oil flowing through porous media; and the lower the permeability is or the higher the

oil viscosity is, the higher the converting temperature will be, as is similar to heavy oil

flowing through a capillary. The lower the permeability of media is, the smaller the pore

radius is. Thus, the extent of the network structure occupying in the porous media is

higher, and the start flowing pressure gradient and yield stress are bigger than that in the

capillary for the same test temperature. The heavy oil start flowing pressure gradient can

be obtained by the extrapolation from the linear relationship of the test data.

3. Characterization of Test Results

3.1. Yield Stress-temperature Relationship

The yield stress for different heavy oils at different temperatures are shown in Table 1,

and it shows an exponential relationship by regression analysis,

TBD a exp.bB/; (4)

wherea and b are the regression coefficients concerning the heavy oil type. Coefficient

a presents the temperature for zero yield stress and the yield stress will reach a large

order of magnitude value when the temperature is lower, so the heavy oil will have

little mobility. Thus, it is very important to choose a reasonable temperature in heavy oil

transportation running in pipes or well bore.

3.2. Converting Temperature of Heavy Oil in Porous Media

The converting temperatures of different heavy oil types through different permeable

porous media are plotted in Figure 3.

It has been shown that the converting temperature decreases as the heavy oil mobility

increases. The converting temperature increases as oil viscosity increases in the same


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352 H. Liu et al.

(a)

(b)

Figure 2. Heavy oil No. 2 flowing through different porous media: (a) 20 meshes sand pack, (b) 40

and 80 meshes sand pack, and (c) 80 meshes sand pack. (continued)

porous media, and decreases as the permeability increases for the same heavy oil. The

converting temperature shows a logarithmic relationship with the mobility of heavy oil

at 50C (Mo50) by regression analysis, which is expressed as follows:

TcD 12:423 ln.Mo50/ C 58:299 R2 D 0:976; (5)

in which,

Mo50 D k=o50: (6)


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354 H. Liu et al.

Figure 4. Start flowing pressure gradient for different heavy oils through differently permeable

porous media.

the start flowing pressure gradient and temperature by regression analysis is shown as

follows:

GoD p0G=L D mlnTC n; (7)where m andn are regression coefficients concerning porous media and oil type, which

can be expressed as follows:

m D 0:203 ln.Mo50/ 0:199 R2 D 0:851; (8)n D 0:94 ln.Mo50/ C 0:783 R2 D 0:861: (9)

4. Deliverability of Thermal Injection Well

4.1. Well Deliverability Relationship

There exists a start flowing pressure gradient for heavy oil, and oil viscosity is the

function of temperature. The existence of a start flowing pressure gradient will affect the

seepage rule and Darcys law in a radial direction. The modified Darcy model, which

is mainly considering the viscous force and the additional resistance, can be shown as

follows (Zhang et al., 1997):

voD 8


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Then, heavy oil production rate (Qo) will be conducted by integral methods when

dp=dr> Go,

QoD2kkrohpi pwGo.re rw/

o.T / ln.re=rw/ ; (11)

and water production rate (Qw) is

QwD 2kkrwh.pi pw/

wln.re=rw/ ; (12)

wherere is the equivalent radius for the five-spot well pattern with well spacing Lw .

S

D.p

2Lw/2

D r2

e: (13)

Thus,

reD Lwp

2=: (14)

4.2. Temperature Limitation for Well Deliverability

Well L33133 is located in Jinglou reservoir block. The buried depth of formation is 346

m. The heavy oil (No. 2) is extra heavy oil with the viscosity of 42,700 mPas, andthe initial temperature is 30.5C. The effective thickness of the reservoir is 3.6 m and

average permeability is 2.1 m2. It is a five-spot well pattern in which well spacing

is in the range of 70 to 140 m. The converting temperature equals 77.9C, which is

obtained by Eq. (5). Formation temperature must exceed the converting temperature

to make the heavy oil start to flow. If the temperature is lower than it, the pressure

difference must be higher than the start flowing pressure. Thus, the temperature limitations

will be different for different well spacings and different pressure differences from

injector to producer, which is shown in Figure 5a and is obtained by Eqs. (7) and

(11). It has been shown that the temperature limitation is decreasing as the pressure

difference is increasing, and the shorter the well spacing is, the faster the temperature

limitation decreases. Also, we can see that if the start flowing pressure gradient is not

considered .GoD 0/, the calculated temperature limitation at some specific pressuredifferences will be lower than the converting temperature 77.9C, even if it is lower

than the temperature limitation that the heavy oil starts to flow at a specific pressure

difference and in this case the heavy oil cant be produced. Therefore, the start flowing

pressure gradient must be considered when some actions, such as heating reservoirs,

placing of well and increasing injection pressure, etc., are taken to develop heavy oil

reservoirs.

The temperature limitations for different production rates are also obtained for the

specific well spacing of 100 m shown in Figure 5b. It will be higher as the production

rate increases, but the increasing tendency is slowing gradually because of the stronger

sensitivity of heavy oil viscosity at higher temperatures. Also, the temperature will be

lower than the converting temperature if the start flowing pressure gradient is neglected.

In this case, the desired production rate cant arrive, and the temperature limitations


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must be calculated again with considering the start flowing pressure gradient .Go 0/. However, it is not necessary when the temperature limitations are higher than the

converting temperature.

5. Conclusions

The experiments of heavy oil flowing through a capillary and porous media are carried

out to study its flowing characteristics. The results show that displacing the pressure

difference increases as heavy oil flowing rate increases and presents a linear tendency for

any specific tested temperature and there exists a converting temperature for heavy oil

flowing through a capillary without additional resistance, and the more viscous the heavy

oil is, the higher the converting temperature is. When the temperature is lower than the

converting temperature, the yield stress for different heavy oils at different temperatures

shows an exponential relationship. It is very important to choose a reasonable temperature

for heavy oil transportation running in pipes and well bore. Also, there exists a convertingtemperature for heavy oil flowing through porous media, and the converting temperatures

for different heavy oils show a logarithmic relationship with the heavy oil mobility at

50C. When the temperature is lower than it, the start flowing pressure gradient through

differently permeable porous media for different heavy oils decreases as a log tendency

with the temperature. It is useful to calculate the suitable displacing pressure difference

or necessary temperature for the development of heavy oil reservoirs.

The start flowing pressure gradient must be considered when some measures are

adopted to develop heavy oil reservoirs or the desired production rate cant arrive, even

the heavy oil doesnt start to flow. And the shorter the well spacing is, the lower the

temperature limitation is, and the faster the temperature limitation decreases. The higher

the total production rate is, the larger the temperature limitation is, but the increasingtendency is slowing gradually.

Acknowledgment

This work was supported by the Major Project of Chinese National Programs for Fun-

damental Research and Development (2011CB201006-06).

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Nomenclature

d diameter of the capillary, m

Go start flowing pressure gradient of heavy oil, kPa/m

h effective thickness of reservoir, m

k absolute permeability of porous media, 103 m2

krw relative permeability of water phase, dimensionless

kro relative permeability of oil phase, dimensionless

L length of capillary or sand pack, m

Lw well spacing, m

Mo50 mobility of heavy oil at 50C, 103 m2/(mPas)

p1 inlet pressure of capillary, Pa

p2 outlet pressure of capillary, Papi bottom hole pressure in injector, kPa

po pressure of oil phase, kPa

pw bottom hole pressure in producer, kPa

pG start flowing pressure difference in capillary, Pa

p0G

start flowing pressure difference in porous media, kPa

Qo production rate of heavy oil, cm3/s

Qw production rate of water, cm3/s

re supply radius of reservoir, m

rw radius of well bore, m

R radius of capillary, m

S area of a well, m2

T temperature, C


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TB temperature corresponding to B , C

Tc converting temperature, C

vo flow speed of heavy oil, cm/s

Greek Symbols

constant, 102

o density of heavy oil, g/cm3

w mobility of water, m2/(Pas)

o.T / mobility of heavy oil atT, m2/(Pas)

o viscosity of heavy oil, mPaso50 oil viscosity at 50

C, mPas shearing stress, Pa

B yield stress, Pa

' porosity of porous media, dimensionless

flow characteristics of heavy oil through porous media

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